diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index a960b96b91c20..8db2904cfd7b7 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -1895,7 +1895,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             if !output_ty
                 .is_privately_uninhabited(self.tcx(), self.infcx.typing_env(self.infcx.param_env))
             {
-                span_mirbug!(self, term, "call to converging function {:?} w/o dest", sig);
+                span_mirbug!(self, term, "call to non-diverging function {:?} w/o dest", sig);
             }
         } else {
             let dest_ty = destination.ty(self.body, tcx).ty;
diff --git a/compiler/rustc_mir_build/src/check_tail_calls.rs b/compiler/rustc_mir_build/src/check_tail_calls.rs
index d4b6da2c14b76..e0cbe8519edd5 100644
--- a/compiler/rustc_mir_build/src/check_tail_calls.rs
+++ b/compiler/rustc_mir_build/src/check_tail_calls.rs
@@ -135,30 +135,23 @@ impl<'tcx> TailCallCkVisitor<'_, 'tcx> {
             self.report_abi_mismatch(expr.span, caller_sig.abi, callee_sig.abi);
         }
 
+        // FIXME(explicit_tail_calls): this currently fails for cases where opaques are used.
+        // e.g.
+        // ```
+        // fn a() -> impl Sized { become b() } // ICE
+        // fn b() -> u8 { 0 }
+        // ```
+        // we should think what is the expected behavior here.
+        // (we should probably just accept this by revealing opaques?)
         if caller_sig.inputs_and_output != callee_sig.inputs_and_output {
-            if caller_sig.inputs() != callee_sig.inputs() {
-                self.report_arguments_mismatch(
-                    expr.span,
-                    self.tcx.liberate_late_bound_regions(
-                        CRATE_DEF_ID.to_def_id(),
-                        self.caller_ty.fn_sig(self.tcx),
-                    ),
-                    self.tcx
-                        .liberate_late_bound_regions(CRATE_DEF_ID.to_def_id(), ty.fn_sig(self.tcx)),
-                );
-            }
-
-            // FIXME(explicit_tail_calls): this currently fails for cases where opaques are used.
-            // e.g.
-            // ```
-            // fn a() -> impl Sized { become b() } // ICE
-            // fn b() -> u8 { 0 }
-            // ```
-            // we should think what is the expected behavior here.
-            // (we should probably just accept this by revealing opaques?)
-            if caller_sig.output() != callee_sig.output() {
-                span_bug!(expr.span, "hir typeck should have checked the return type already");
-            }
+            self.report_signature_mismatch(
+                expr.span,
+                self.tcx.liberate_late_bound_regions(
+                    CRATE_DEF_ID.to_def_id(),
+                    self.caller_ty.fn_sig(self.tcx),
+                ),
+                self.tcx.liberate_late_bound_regions(CRATE_DEF_ID.to_def_id(), ty.fn_sig(self.tcx)),
+            );
         }
 
         {
@@ -365,7 +358,7 @@ impl<'tcx> TailCallCkVisitor<'_, 'tcx> {
         self.found_errors = Err(err);
     }
 
-    fn report_arguments_mismatch(
+    fn report_signature_mismatch(
         &mut self,
         sp: Span,
         caller_sig: ty::FnSig<'_>,
diff --git a/library/std_detect/src/detect/os/riscv.rs b/library/std_detect/src/detect/os/riscv.rs
index c6acbd3525bd3..9b9e0cba09d1c 100644
--- a/library/std_detect/src/detect/os/riscv.rs
+++ b/library/std_detect/src/detect/os/riscv.rs
@@ -119,11 +119,31 @@ pub(crate) fn imply_features(mut value: cache::Initializer) -> cache::Initialize
         imply!(d | zfhmin | zfa => f);
         imply!(zfbfmin => f); // and some of (not all) "Zfh" instructions.
 
-        // Relatively complex implication rules from the "C" extension.
+        // Relatively complex implication rules around the "C" extension.
+        // (from "C" and some others)
         imply!(c => zca);
         imply!(c & d => zcd);
         #[cfg(target_arch = "riscv32")]
         imply!(c & f => zcf);
+        // (to "C"; defined as superset)
+        cfg_select! {
+            target_arch = "riscv32" => {
+                if value.test(Feature::d as u32) {
+                    imply!(zcf & zcd => c);
+                } else if value.test(Feature::f as u32) {
+                    imply!(zcf => c);
+                } else {
+                    imply!(zca => c);
+                }
+            }
+            _ => {
+                if value.test(Feature::d as u32) {
+                    imply!(zcd => c);
+                } else {
+                    imply!(zca => c);
+                }
+            }
+        }
 
         imply!(zicntr | zihpm | f | zfinx | zve32x => zicsr);
 
diff --git a/src/bootstrap/src/core/build_steps/test.rs b/src/bootstrap/src/core/build_steps/test.rs
index e7a57a7f3755b..56e7582a6ffda 100644
--- a/src/bootstrap/src/core/build_steps/test.rs
+++ b/src/bootstrap/src/core/build_steps/test.rs
@@ -1830,10 +1830,27 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
         cmd.arg("--host").arg(&*compiler.host.triple);
         cmd.arg("--llvm-filecheck").arg(builder.llvm_filecheck(builder.config.host_target));
 
-        if let Some(codegen_backend) = builder.config.default_codegen_backend(compiler.host) {
-            // Tells compiletest which codegen backend is used by default by the compiler.
+        if let Some(codegen_backend) = builder.config.cmd.test_codegen_backend() {
+            if !builder.config.enabled_codegen_backends(compiler.host).contains(codegen_backend) {
+                eprintln!(
+                    "\
+ERROR: No configured backend named `{name}`
+HELP: You can add it into `bootstrap.toml` in `rust.codegen-backends = [{name:?}]`",
+                    name = codegen_backend.name(),
+                );
+                crate::exit!(1);
+            }
+            // Tells compiletest that we want to use this codegen in particular and to override
+            // the default one.
+            cmd.arg("--override-codegen-backend").arg(codegen_backend.name());
+            // Tells compiletest which codegen backend to use.
+            // It is used to e.g. ignore tests that don't support that codegen backend.
+            cmd.arg("--default-codegen-backend").arg(codegen_backend.name());
+        } else {
+            // Tells compiletest which codegen backend to use.
             // It is used to e.g. ignore tests that don't support that codegen backend.
-            cmd.arg("--codegen-backend").arg(codegen_backend.name());
+            cmd.arg("--default-codegen-backend")
+                .arg(builder.config.default_codegen_backend(compiler.host).unwrap().name());
         }
 
         if builder.build.config.llvm_enzyme {
diff --git a/src/bootstrap/src/core/builder/cargo.rs b/src/bootstrap/src/core/builder/cargo.rs
index 69a744a86cb85..721924034123e 100644
--- a/src/bootstrap/src/core/builder/cargo.rs
+++ b/src/bootstrap/src/core/builder/cargo.rs
@@ -1326,7 +1326,12 @@ impl Builder<'_> {
 
             if let Some(limit) = limit
                 && (build_compiler_stage == 0
-                    || self.config.default_codegen_backend(target).unwrap_or_default().is_llvm())
+                    || self
+                        .config
+                        .default_codegen_backend(target)
+                        .cloned()
+                        .unwrap_or_default()
+                        .is_llvm())
             {
                 rustflags.arg(&format!("-Cllvm-args=-import-instr-limit={limit}"));
             }
diff --git a/src/bootstrap/src/core/config/config.rs b/src/bootstrap/src/core/config/config.rs
index 5eea54360238d..d0647537e5668 100644
--- a/src/bootstrap/src/core/config/config.rs
+++ b/src/bootstrap/src/core/config/config.rs
@@ -1755,8 +1755,8 @@ impl Config {
 
     /// Returns the codegen backend that should be configured as the *default* codegen backend
     /// for a rustc compiled by bootstrap.
-    pub fn default_codegen_backend(&self, target: TargetSelection) -> Option<CodegenBackendKind> {
-        self.enabled_codegen_backends(target).first().cloned()
+    pub fn default_codegen_backend(&self, target: TargetSelection) -> Option<&CodegenBackendKind> {
+        self.enabled_codegen_backends(target).first()
     }
 
     pub fn jemalloc(&self, target: TargetSelection) -> bool {
diff --git a/src/bootstrap/src/core/config/flags.rs b/src/bootstrap/src/core/config/flags.rs
index 17bfb388280a9..c01b71b926068 100644
--- a/src/bootstrap/src/core/config/flags.rs
+++ b/src/bootstrap/src/core/config/flags.rs
@@ -15,7 +15,7 @@ use crate::core::build_steps::setup::Profile;
 use crate::core::builder::{Builder, Kind};
 use crate::core::config::Config;
 use crate::core::config::target_selection::{TargetSelectionList, target_selection_list};
-use crate::{Build, DocTests};
+use crate::{Build, CodegenBackendKind, DocTests};
 
 #[derive(Copy, Clone, Default, Debug, ValueEnum)]
 pub enum Color {
@@ -419,6 +419,9 @@ pub enum Subcommand {
         #[arg(long)]
         /// don't capture stdout/stderr of tests
         no_capture: bool,
+        #[arg(long)]
+        /// Use a different codegen backend when running tests.
+        test_codegen_backend: Option<CodegenBackendKind>,
     },
     /// Build and run some test suites *in Miri*
     Miri {
@@ -658,6 +661,13 @@ impl Subcommand {
             _ => vec![],
         }
     }
+
+    pub fn test_codegen_backend(&self) -> Option<&CodegenBackendKind> {
+        match self {
+            Subcommand::Test { test_codegen_backend, .. } => test_codegen_backend.as_ref(),
+            _ => None,
+        }
+    }
 }
 
 /// Returns the shell completion for a given shell, if the result differs from the current
diff --git a/src/bootstrap/src/lib.rs b/src/bootstrap/src/lib.rs
index 8f766ed00a5be..ec7edbf753129 100644
--- a/src/bootstrap/src/lib.rs
+++ b/src/bootstrap/src/lib.rs
@@ -165,6 +165,20 @@ impl CodegenBackendKind {
     }
 }
 
+impl std::str::FromStr for CodegenBackendKind {
+    type Err = &'static str;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s.to_lowercase().as_str() {
+            "" => Err("Invalid empty backend name"),
+            "gcc" => Ok(Self::Gcc),
+            "llvm" => Ok(Self::Llvm),
+            "cranelift" => Ok(Self::Cranelift),
+            _ => Ok(Self::Custom(s.to_string())),
+        }
+    }
+}
+
 #[derive(PartialEq, Eq, Copy, Clone, Debug)]
 pub enum DocTests {
     /// Run normal tests and doc tests (default).
diff --git a/src/bootstrap/src/utils/change_tracker.rs b/src/bootstrap/src/utils/change_tracker.rs
index b2f9960a4492a..4fb5891ed181a 100644
--- a/src/bootstrap/src/utils/change_tracker.rs
+++ b/src/bootstrap/src/utils/change_tracker.rs
@@ -506,6 +506,11 @@ pub const CONFIG_CHANGE_HISTORY: &[ChangeInfo] = &[
         severity: ChangeSeverity::Warning,
         summary: "It is no longer possible to `x clippy` with stage 0. All clippy commands have to be on stage 1+.",
     },
+    ChangeInfo {
+        change_id: 145256,
+        severity: ChangeSeverity::Info,
+        summary: "Added `--test-codegen-backend` CLI option for tests",
+    },
     ChangeInfo {
         change_id: 145379,
         severity: ChangeSeverity::Info,
diff --git a/src/etc/completions/x.fish b/src/etc/completions/x.fish
index 0b9af33421461..544f9b97237cb 100644
--- a/src/etc/completions/x.fish
+++ b/src/etc/completions/x.fish
@@ -305,6 +305,7 @@ complete -c x -n "__fish_x_using_subcommand test" -l extra-checks -d 'comma-sepa
 complete -c x -n "__fish_x_using_subcommand test" -l compare-mode -d 'mode describing what file the actual ui output will be compared to' -r
 complete -c x -n "__fish_x_using_subcommand test" -l pass -d 'force {check,build,run}-pass tests to this mode' -r
 complete -c x -n "__fish_x_using_subcommand test" -l run -d 'whether to execute run-* tests' -r
+complete -c x -n "__fish_x_using_subcommand test" -l test-codegen-backend -d 'Use a different codegen backend when running tests' -r
 complete -c x -n "__fish_x_using_subcommand test" -l config -d 'TOML configuration file for build' -r -F
 complete -c x -n "__fish_x_using_subcommand test" -l build-dir -d 'Build directory, overrides `build.build-dir` in `bootstrap.toml`' -r -f -a "(__fish_complete_directories)"
 complete -c x -n "__fish_x_using_subcommand test" -l build -d 'host target of the stage0 compiler' -r -f
diff --git a/src/etc/completions/x.ps1 b/src/etc/completions/x.ps1
index 95cee4b633625..b03acf930f70d 100644
--- a/src/etc/completions/x.ps1
+++ b/src/etc/completions/x.ps1
@@ -351,6 +351,7 @@ Register-ArgumentCompleter -Native -CommandName 'x' -ScriptBlock {
             [CompletionResult]::new('--compare-mode', '--compare-mode', [CompletionResultType]::ParameterName, 'mode describing what file the actual ui output will be compared to')
             [CompletionResult]::new('--pass', '--pass', [CompletionResultType]::ParameterName, 'force {check,build,run}-pass tests to this mode')
             [CompletionResult]::new('--run', '--run', [CompletionResultType]::ParameterName, 'whether to execute run-* tests')
+            [CompletionResult]::new('--test-codegen-backend', '--test-codegen-backend', [CompletionResultType]::ParameterName, 'Use a different codegen backend when running tests')
             [CompletionResult]::new('--config', '--config', [CompletionResultType]::ParameterName, 'TOML configuration file for build')
             [CompletionResult]::new('--build-dir', '--build-dir', [CompletionResultType]::ParameterName, 'Build directory, overrides `build.build-dir` in `bootstrap.toml`')
             [CompletionResult]::new('--build', '--build', [CompletionResultType]::ParameterName, 'host target of the stage0 compiler')
diff --git a/src/etc/completions/x.py.fish b/src/etc/completions/x.py.fish
index 6fba6a4562368..08e4cd26ce887 100644
--- a/src/etc/completions/x.py.fish
+++ b/src/etc/completions/x.py.fish
@@ -305,6 +305,7 @@ complete -c x.py -n "__fish_x.py_using_subcommand test" -l extra-checks -d 'comm
 complete -c x.py -n "__fish_x.py_using_subcommand test" -l compare-mode -d 'mode describing what file the actual ui output will be compared to' -r
 complete -c x.py -n "__fish_x.py_using_subcommand test" -l pass -d 'force {check,build,run}-pass tests to this mode' -r
 complete -c x.py -n "__fish_x.py_using_subcommand test" -l run -d 'whether to execute run-* tests' -r
+complete -c x.py -n "__fish_x.py_using_subcommand test" -l test-codegen-backend -d 'Use a different codegen backend when running tests' -r
 complete -c x.py -n "__fish_x.py_using_subcommand test" -l config -d 'TOML configuration file for build' -r -F
 complete -c x.py -n "__fish_x.py_using_subcommand test" -l build-dir -d 'Build directory, overrides `build.build-dir` in `bootstrap.toml`' -r -f -a "(__fish_complete_directories)"
 complete -c x.py -n "__fish_x.py_using_subcommand test" -l build -d 'host target of the stage0 compiler' -r -f
diff --git a/src/etc/completions/x.py.ps1 b/src/etc/completions/x.py.ps1
index 458879a17a7b9..3d95d88af4955 100644
--- a/src/etc/completions/x.py.ps1
+++ b/src/etc/completions/x.py.ps1
@@ -351,6 +351,7 @@ Register-ArgumentCompleter -Native -CommandName 'x.py' -ScriptBlock {
             [CompletionResult]::new('--compare-mode', '--compare-mode', [CompletionResultType]::ParameterName, 'mode describing what file the actual ui output will be compared to')
             [CompletionResult]::new('--pass', '--pass', [CompletionResultType]::ParameterName, 'force {check,build,run}-pass tests to this mode')
             [CompletionResult]::new('--run', '--run', [CompletionResultType]::ParameterName, 'whether to execute run-* tests')
+            [CompletionResult]::new('--test-codegen-backend', '--test-codegen-backend', [CompletionResultType]::ParameterName, 'Use a different codegen backend when running tests')
             [CompletionResult]::new('--config', '--config', [CompletionResultType]::ParameterName, 'TOML configuration file for build')
             [CompletionResult]::new('--build-dir', '--build-dir', [CompletionResultType]::ParameterName, 'Build directory, overrides `build.build-dir` in `bootstrap.toml`')
             [CompletionResult]::new('--build', '--build', [CompletionResultType]::ParameterName, 'host target of the stage0 compiler')
diff --git a/src/etc/completions/x.py.sh b/src/etc/completions/x.py.sh
index e003bf7fd0b43..8ff0eaf35c89a 100644
--- a/src/etc/completions/x.py.sh
+++ b/src/etc/completions/x.py.sh
@@ -3875,7 +3875,7 @@ _x.py() {
             return 0
             ;;
         x.py__test)
-            opts="-v -i -j -h --no-fail-fast --test-args --compiletest-rustc-args --no-doc --doc --bless --extra-checks --force-rerun --only-modified --compare-mode --pass --run --rustfix-coverage --no-capture --verbose --incremental --config --build-dir --build --host --target --exclude --skip --include-default-paths --rustc-error-format --on-fail --dry-run --dump-bootstrap-shims --stage --keep-stage --keep-stage-std --src --jobs --warnings --json-output --compile-time-deps --color --bypass-bootstrap-lock --rust-profile-generate --rust-profile-use --llvm-profile-use --llvm-profile-generate --enable-bolt-settings --skip-stage0-validation --reproducible-artifact --set --ci --skip-std-check-if-no-download-rustc --help [PATHS]... [ARGS]..."
+            opts="-v -i -j -h --no-fail-fast --test-args --compiletest-rustc-args --no-doc --doc --bless --extra-checks --force-rerun --only-modified --compare-mode --pass --run --rustfix-coverage --no-capture --test-codegen-backend --verbose --incremental --config --build-dir --build --host --target --exclude --skip --include-default-paths --rustc-error-format --on-fail --dry-run --dump-bootstrap-shims --stage --keep-stage --keep-stage-std --src --jobs --warnings --json-output --compile-time-deps --color --bypass-bootstrap-lock --rust-profile-generate --rust-profile-use --llvm-profile-use --llvm-profile-generate --enable-bolt-settings --skip-stage0-validation --reproducible-artifact --set --ci --skip-std-check-if-no-download-rustc --help [PATHS]... [ARGS]..."
             if [[ ${cur} == -* || ${COMP_CWORD} -eq 2 ]] ; then
                 COMPREPLY=( $(compgen -W "${opts}" -- "${cur}") )
                 return 0
@@ -3905,6 +3905,10 @@ _x.py() {
                     COMPREPLY=($(compgen -f "${cur}"))
                     return 0
                     ;;
+                --test-codegen-backend)
+                    COMPREPLY=($(compgen -f "${cur}"))
+                    return 0
+                    ;;
                 --config)
                     local oldifs
                     if [ -n "${IFS+x}" ]; then
diff --git a/src/etc/completions/x.py.zsh b/src/etc/completions/x.py.zsh
index b82c2d65e8694..9d2d73e582ec6 100644
--- a/src/etc/completions/x.py.zsh
+++ b/src/etc/completions/x.py.zsh
@@ -351,6 +351,7 @@ _arguments "${_arguments_options[@]}" : \
 '--compare-mode=[mode describing what file the actual ui output will be compared to]:COMPARE MODE:_default' \
 '--pass=[force {check,build,run}-pass tests to this mode]:check | build | run:_default' \
 '--run=[whether to execute run-* tests]:auto | always | never:_default' \
+'--test-codegen-backend=[Use a different codegen backend when running tests]:TEST_CODEGEN_BACKEND:_default' \
 '--config=[TOML configuration file for build]:FILE:_files' \
 '--build-dir=[Build directory, overrides \`build.build-dir\` in \`bootstrap.toml\`]:DIR:_files -/' \
 '--build=[host target of the stage0 compiler]:BUILD:' \
diff --git a/src/etc/completions/x.sh b/src/etc/completions/x.sh
index c2cb771002017..c1b73fb7c9e34 100644
--- a/src/etc/completions/x.sh
+++ b/src/etc/completions/x.sh
@@ -3875,7 +3875,7 @@ _x() {
             return 0
             ;;
         x__test)
-            opts="-v -i -j -h --no-fail-fast --test-args --compiletest-rustc-args --no-doc --doc --bless --extra-checks --force-rerun --only-modified --compare-mode --pass --run --rustfix-coverage --no-capture --verbose --incremental --config --build-dir --build --host --target --exclude --skip --include-default-paths --rustc-error-format --on-fail --dry-run --dump-bootstrap-shims --stage --keep-stage --keep-stage-std --src --jobs --warnings --json-output --compile-time-deps --color --bypass-bootstrap-lock --rust-profile-generate --rust-profile-use --llvm-profile-use --llvm-profile-generate --enable-bolt-settings --skip-stage0-validation --reproducible-artifact --set --ci --skip-std-check-if-no-download-rustc --help [PATHS]... [ARGS]..."
+            opts="-v -i -j -h --no-fail-fast --test-args --compiletest-rustc-args --no-doc --doc --bless --extra-checks --force-rerun --only-modified --compare-mode --pass --run --rustfix-coverage --no-capture --test-codegen-backend --verbose --incremental --config --build-dir --build --host --target --exclude --skip --include-default-paths --rustc-error-format --on-fail --dry-run --dump-bootstrap-shims --stage --keep-stage --keep-stage-std --src --jobs --warnings --json-output --compile-time-deps --color --bypass-bootstrap-lock --rust-profile-generate --rust-profile-use --llvm-profile-use --llvm-profile-generate --enable-bolt-settings --skip-stage0-validation --reproducible-artifact --set --ci --skip-std-check-if-no-download-rustc --help [PATHS]... [ARGS]..."
             if [[ ${cur} == -* || ${COMP_CWORD} -eq 2 ]] ; then
                 COMPREPLY=( $(compgen -W "${opts}" -- "${cur}") )
                 return 0
@@ -3905,6 +3905,10 @@ _x() {
                     COMPREPLY=($(compgen -f "${cur}"))
                     return 0
                     ;;
+                --test-codegen-backend)
+                    COMPREPLY=($(compgen -f "${cur}"))
+                    return 0
+                    ;;
                 --config)
                     local oldifs
                     if [ -n "${IFS+x}" ]; then
diff --git a/src/etc/completions/x.zsh b/src/etc/completions/x.zsh
index 49139e70f7fb2..29237ef9bf8fd 100644
--- a/src/etc/completions/x.zsh
+++ b/src/etc/completions/x.zsh
@@ -351,6 +351,7 @@ _arguments "${_arguments_options[@]}" : \
 '--compare-mode=[mode describing what file the actual ui output will be compared to]:COMPARE MODE:_default' \
 '--pass=[force {check,build,run}-pass tests to this mode]:check | build | run:_default' \
 '--run=[whether to execute run-* tests]:auto | always | never:_default' \
+'--test-codegen-backend=[Use a different codegen backend when running tests]:TEST_CODEGEN_BACKEND:_default' \
 '--config=[TOML configuration file for build]:FILE:_files' \
 '--build-dir=[Build directory, overrides \`build.build-dir\` in \`bootstrap.toml\`]:DIR:_files -/' \
 '--build=[host target of the stage0 compiler]:BUILD:' \
diff --git a/src/librustdoc/html/static/js/search.js b/src/librustdoc/html/static/js/search.js
index d55208150b843..42b87d562529b 100644
--- a/src/librustdoc/html/static/js/search.js
+++ b/src/librustdoc/html/static/js/search.js
@@ -5252,7 +5252,7 @@ if (typeof window !== "undefined") {
         },
         loadTreeByHash: hashHex => {
             const script = document.createElement("script");
-            script.src = `${ROOT_PATH}/search.index/${hashHex}.js`;
+            script.src = `${ROOT_PATH}search.index/${hashHex}.js`;
             script.onerror = e => {
                 if (databaseCallbacks) {
                     databaseCallbacks.err_rn_(hashHex, e);
@@ -5262,7 +5262,7 @@ if (typeof window !== "undefined") {
         },
         loadDataByNameAndHash: (name, hashHex) => {
             const script = document.createElement("script");
-            script.src = `${ROOT_PATH}/search.index/${name}/${hashHex}.js`;
+            script.src = `${ROOT_PATH}search.index/${name}/${hashHex}.js`;
             script.onerror = e => {
                 if (databaseCallbacks) {
                     databaseCallbacks.err_rd_(hashHex, e);
diff --git a/src/tools/compiletest/src/common.rs b/src/tools/compiletest/src/common.rs
index 2d49b1a7097d0..7fc80c1edb158 100644
--- a/src/tools/compiletest/src/common.rs
+++ b/src/tools/compiletest/src/common.rs
@@ -692,7 +692,9 @@ pub struct Config {
     pub minicore_path: Utf8PathBuf,
 
     /// Current codegen backend used.
-    pub codegen_backend: CodegenBackend,
+    pub default_codegen_backend: CodegenBackend,
+    /// Name/path of the backend to use instead of `default_codegen_backend`.
+    pub override_codegen_backend: Option<String>,
 }
 
 impl Config {
@@ -796,7 +798,8 @@ impl Config {
             profiler_runtime: Default::default(),
             diff_command: Default::default(),
             minicore_path: Default::default(),
-            codegen_backend: CodegenBackend::Llvm,
+            default_codegen_backend: CodegenBackend::Llvm,
+            override_codegen_backend: None,
         }
     }
 
diff --git a/src/tools/compiletest/src/directives.rs b/src/tools/compiletest/src/directives.rs
index 13e694b7f03ca..00007aa1d6683 100644
--- a/src/tools/compiletest/src/directives.rs
+++ b/src/tools/compiletest/src/directives.rs
@@ -1624,7 +1624,7 @@ fn ignore_backends(
                 }
             }
         }) {
-            if config.codegen_backend == backend {
+            if config.default_codegen_backend == backend {
                 return IgnoreDecision::Ignore {
                     reason: format!("{} backend is marked as ignore", backend.as_str()),
                 };
@@ -1651,12 +1651,12 @@ fn needs_backends(
                     panic!("Invalid needs-backends value `{backend}` in `{path}`: {error}")
                 }
             })
-            .any(|backend| config.codegen_backend == backend)
+            .any(|backend| config.default_codegen_backend == backend)
         {
             return IgnoreDecision::Ignore {
                 reason: format!(
                     "{} backend is not part of required backends",
-                    config.codegen_backend.as_str()
+                    config.default_codegen_backend.as_str()
                 ),
             };
         }
diff --git a/src/tools/compiletest/src/lib.rs b/src/tools/compiletest/src/lib.rs
index f5409e783418b..469dd68207edc 100644
--- a/src/tools/compiletest/src/lib.rs
+++ b/src/tools/compiletest/src/lib.rs
@@ -212,9 +212,15 @@ pub fn parse_config(args: Vec<String>) -> Config {
         )
         .optopt(
             "",
-            "codegen-backend",
+            "default-codegen-backend",
             "the codegen backend currently used",
             "CODEGEN BACKEND NAME",
+        )
+        .optopt(
+            "",
+            "override-codegen-backend",
+            "the codegen backend to use instead of the default one",
+            "CODEGEN BACKEND [NAME | PATH]",
         );
 
     let (argv0, args_) = args.split_first().unwrap();
@@ -276,14 +282,17 @@ pub fn parse_config(args: Vec<String>) -> Config {
             || directives::extract_llvm_version_from_binary(&matches.opt_str("llvm-filecheck")?),
         );
 
-    let codegen_backend = match matches.opt_str("codegen-backend").as_deref() {
+    let default_codegen_backend = match matches.opt_str("default-codegen-backend").as_deref() {
         Some(backend) => match CodegenBackend::try_from(backend) {
             Ok(backend) => backend,
-            Err(error) => panic!("invalid value `{backend}` for `--codegen-backend`: {error}"),
+            Err(error) => {
+                panic!("invalid value `{backend}` for `--defalt-codegen-backend`: {error}")
+            }
         },
         // By default, it's always llvm.
         None => CodegenBackend::Llvm,
     };
+    let override_codegen_backend = matches.opt_str("override-codegen-backend");
 
     let run_ignored = matches.opt_present("ignored");
     let with_rustc_debug_assertions = matches.opt_present("with-rustc-debug-assertions");
@@ -472,7 +481,8 @@ pub fn parse_config(args: Vec<String>) -> Config {
 
         minicore_path: opt_path(matches, "minicore-path"),
 
-        codegen_backend,
+        default_codegen_backend,
+        override_codegen_backend,
     }
 }
 
@@ -812,13 +822,13 @@ fn collect_tests_from_dir(
         && let Some(Utf8Component::Normal(parent)) = components.next()
         && parent == "tests"
         && let Ok(backend) = CodegenBackend::try_from(backend)
-        && backend != cx.config.codegen_backend
+        && backend != cx.config.default_codegen_backend
     {
         // We ignore asm tests which don't match the current codegen backend.
         warning!(
             "Ignoring tests in `{dir}` because they don't match the configured codegen \
              backend (`{}`)",
-            cx.config.codegen_backend.as_str(),
+            cx.config.default_codegen_backend.as_str(),
         );
         return Ok(TestCollector::new());
     }
diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index 821cb12864764..2402ed9a950f2 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -1558,6 +1558,11 @@ impl<'test> TestCx<'test> {
             rustc.arg("--sysroot").arg(&self.config.sysroot_base);
         }
 
+        // If the provided codegen backend is not LLVM, we need to pass it.
+        if let Some(ref backend) = self.config.override_codegen_backend {
+            rustc.arg(format!("-Zcodegen-backend={}", backend));
+        }
+
         // Optionally prevent default --target if specified in test compile-flags.
         let custom_target = self.props.compile_flags.iter().any(|x| x.starts_with("--target"));
 
diff --git a/src/tools/miri/.github/workflows/ci.yml b/src/tools/miri/.github/workflows/ci.yml
index c47f9695624bc..7d79c384f85a3 100644
--- a/src/tools/miri/.github/workflows/ci.yml
+++ b/src/tools/miri/.github/workflows/ci.yml
@@ -69,12 +69,6 @@ jobs:
           sudo apt update
           # Install needed packages
           sudo apt install $(echo "libatomic1: zlib1g-dev:" | sed 's/:/:${{ matrix.multiarch }}/g')
-      - name: Install rustup on Windows ARM
-        if: ${{ matrix.os == 'windows-11-arm' }}
-        run: |
-            curl -LOs https://static.rust-lang.org/rustup/dist/aarch64-pc-windows-msvc/rustup-init.exe
-            ./rustup-init.exe -y --no-modify-path
-            echo "$USERPROFILE/.cargo/bin" >> "$GITHUB_PATH"
       - uses: ./.github/workflows/setup
         with:
           toolchain_flags: "--host ${{ matrix.host_target }}"
@@ -169,7 +163,13 @@ jobs:
         run: rustup toolchain install nightly --profile minimal
       - name: Install rustup-toolchain-install-master
         run: cargo install -f rustup-toolchain-install-master
-      - name: Push changes to a branch and create PR
+      # Create a token for the next step so it can create a PR that actually runs CI.
+      - uses: actions/create-github-app-token@v2
+        id: app-token
+        with:
+          app-id: ${{ vars.APP_CLIENT_ID }}
+          private-key: ${{ secrets.APP_PRIVATE_KEY }}
+      - name: pull changes from rustc and create PR
         run: |
           # Make it easier to see what happens.
           set -x
@@ -198,9 +198,9 @@ jobs:
           BRANCH="rustup-$(date -u +%Y-%m-%d)"
           git switch -c $BRANCH
           git push -u origin $BRANCH
-          gh pr create -B master --title 'Automatic Rustup' --body 'Please close and re-open this PR to trigger CI, then enable auto-merge.'
+          gh pr create -B master --title 'Automatic Rustup' --body "Update \`rustc\` to https://github.com/rust-lang/rust/commit/$(cat rust-version)."
         env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GITHUB_TOKEN: ${{ steps.app-token.outputs.token }}
 
   cron-fail-notify:
     name: cronjob failure notification
diff --git a/src/tools/miri/Cargo.toml b/src/tools/miri/Cargo.toml
index 91dadf78a2f72..99111092d39e7 100644
--- a/src/tools/miri/Cargo.toml
+++ b/src/tools/miri/Cargo.toml
@@ -78,6 +78,7 @@ native-lib = ["dep:libffi", "dep:libloading", "dep:capstone", "dep:ipc-channel",
 
 [lints.rust.unexpected_cfgs]
 level = "warn"
+check-cfg = ['cfg(bootstrap)']
 
 # Be aware that this file is inside a workspace when used via the
 # submodule in the rustc repo. That means there are many cargo features
diff --git a/src/tools/miri/rust-version b/src/tools/miri/rust-version
index 2178caf63968a..59adc572eaa4b 100644
--- a/src/tools/miri/rust-version
+++ b/src/tools/miri/rust-version
@@ -1 +1 @@
-733dab558992d902d6d17576de1da768094e2cf3
+f605b57042ffeb320d7ae44490113a827139b766
diff --git a/src/tools/miri/src/diagnostics.rs b/src/tools/miri/src/diagnostics.rs
index 9ecbd31c5b9f9..b5ca9601547eb 100644
--- a/src/tools/miri/src/diagnostics.rs
+++ b/src/tools/miri/src/diagnostics.rs
@@ -282,7 +282,8 @@ pub fn report_error<'tcx>(
             },
             TreeBorrowsUb { title: _, details, history } => {
                 let mut helps = vec![
-                    note!("this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental")
+                    note!("this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental"),
+                    note!("see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information"),
                 ];
                 for m in details {
                     helps.push(note!("{m}"));
diff --git a/src/tools/miri/src/machine.rs b/src/tools/miri/src/machine.rs
index 4cad36cf3831c..52c4bd142c62c 100644
--- a/src/tools/miri/src/machine.rs
+++ b/src/tools/miri/src/machine.rs
@@ -12,10 +12,10 @@ use rand::rngs::StdRng;
 use rand::{Rng, SeedableRng};
 use rustc_abi::{Align, ExternAbi, Size};
 use rustc_apfloat::{Float, FloatConvert};
-use rustc_hir::attrs::InlineAttr;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 #[allow(unused)]
 use rustc_data_structures::static_assert_size;
+use rustc_hir::attrs::InlineAttr;
 use rustc_middle::mir;
 use rustc_middle::query::TyCtxtAt;
 use rustc_middle::ty::layout::{
@@ -1396,6 +1396,7 @@ impl<'tcx> Machine<'tcx> for MiriMachine<'tcx> {
             GlobalDataRaceHandler::Genmc(genmc_ctx) =>
                 genmc_ctx.memory_load(machine, ptr.addr(), range.size)?,
             GlobalDataRaceHandler::Vclocks(_data_race) => {
+                let _trace = enter_trace_span!(data_race::before_memory_read);
                 let AllocDataRaceHandler::Vclocks(data_race, weak_memory) = &alloc_extra.data_race
                 else {
                     unreachable!();
@@ -1431,6 +1432,7 @@ impl<'tcx> Machine<'tcx> for MiriMachine<'tcx> {
                 genmc_ctx.memory_store(machine, ptr.addr(), range.size)?;
             }
             GlobalDataRaceHandler::Vclocks(_global_state) => {
+                let _trace = enter_trace_span!(data_race::before_memory_write);
                 let AllocDataRaceHandler::Vclocks(data_race, weak_memory) =
                     &mut alloc_extra.data_race
                 else {
@@ -1467,6 +1469,7 @@ impl<'tcx> Machine<'tcx> for MiriMachine<'tcx> {
             GlobalDataRaceHandler::Genmc(genmc_ctx) =>
                 genmc_ctx.handle_dealloc(machine, ptr.addr(), size, align, kind)?,
             GlobalDataRaceHandler::Vclocks(_global_state) => {
+                let _trace = enter_trace_span!(data_race::before_memory_deallocation);
                 let data_race = alloc_extra.data_race.as_vclocks_mut().unwrap();
                 data_race.write(
                     alloc_id,
@@ -1677,6 +1680,7 @@ impl<'tcx> Machine<'tcx> for MiriMachine<'tcx> {
         local: mir::Local,
     ) -> InterpResult<'tcx> {
         if let Some(data_race) = &frame.extra.data_race {
+            let _trace = enter_trace_span!(data_race::after_local_read);
             data_race.local_read(local, &ecx.machine);
         }
         interp_ok(())
@@ -1688,6 +1692,7 @@ impl<'tcx> Machine<'tcx> for MiriMachine<'tcx> {
         storage_live: bool,
     ) -> InterpResult<'tcx> {
         if let Some(data_race) = &ecx.frame().extra.data_race {
+            let _trace = enter_trace_span!(data_race::after_local_write);
             data_race.local_write(local, storage_live, &ecx.machine);
         }
         interp_ok(())
@@ -1710,6 +1715,7 @@ impl<'tcx> Machine<'tcx> for MiriMachine<'tcx> {
         if let Some(data_race) =
             &machine.threads.active_thread_stack().last().unwrap().extra.data_race
         {
+            let _trace = enter_trace_span!(data_race::after_local_moved_to_memory);
             data_race.local_moved_to_memory(
                 local,
                 alloc_info.data_race.as_vclocks_mut().unwrap(),
diff --git a/src/tools/miri/src/operator.rs b/src/tools/miri/src/operator.rs
index 3c3f2c2853588..116f45f18dda6 100644
--- a/src/tools/miri/src/operator.rs
+++ b/src/tools/miri/src/operator.rs
@@ -57,7 +57,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 let ptr = left.to_scalar().to_pointer(this)?;
                 // We do the actual operation with usize-typed scalars.
                 let left = ImmTy::from_uint(ptr.addr().bytes(), this.machine.layouts.usize);
-                let result = this.binary_op(bin_op, &left, &right)?;
+                let result = this.binary_op(bin_op, &left, right)?;
                 // Construct a new pointer with the provenance of `ptr` (the LHS).
                 let result_ptr = Pointer::new(
                     ptr.provenance,
diff --git a/src/tools/miri/src/shims/extern_static.rs b/src/tools/miri/src/shims/extern_static.rs
index 49c0c380a08ab..c2527bf8e25d4 100644
--- a/src/tools/miri/src/shims/extern_static.rs
+++ b/src/tools/miri/src/shims/extern_static.rs
@@ -62,7 +62,7 @@ impl<'tcx> MiriMachine<'tcx> {
             }
             "android" => {
                 Self::null_ptr_extern_statics(ecx, &["bsd_signal"])?;
-                Self::weak_symbol_extern_statics(ecx, &["signal", "getrandom"])?;
+                Self::weak_symbol_extern_statics(ecx, &["signal", "getrandom", "gettid"])?;
             }
             "windows" => {
                 // "_tls_used"
diff --git a/src/tools/miri/src/shims/foreign_items.rs b/src/tools/miri/src/shims/foreign_items.rs
index 23b1d0c4f6ecf..a700644b95d82 100644
--- a/src/tools/miri/src/shims/foreign_items.rs
+++ b/src/tools/miri/src/shims/foreign_items.rs
@@ -5,6 +5,7 @@ use std::path::Path;
 use rustc_abi::{Align, AlignFromBytesError, CanonAbi, Size};
 use rustc_apfloat::Float;
 use rustc_ast::expand::allocator::alloc_error_handler_name;
+use rustc_hir::attrs::Linkage;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::CrateNum;
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
@@ -138,7 +139,13 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
             Entry::Occupied(e) => e.into_mut(),
             Entry::Vacant(e) => {
                 // Find it if it was not cached.
-                let mut instance_and_crate: Option<(ty::Instance<'_>, CrateNum)> = None;
+
+                struct SymbolTarget<'tcx> {
+                    instance: ty::Instance<'tcx>,
+                    cnum: CrateNum,
+                    is_weak: bool,
+                }
+                let mut symbol_target: Option<SymbolTarget<'tcx>> = None;
                 helpers::iter_exported_symbols(tcx, |cnum, def_id| {
                     let attrs = tcx.codegen_fn_attrs(def_id);
                     // Skip over imports of items.
@@ -155,40 +162,80 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 
                     let instance = Instance::mono(tcx, def_id);
                     let symbol_name = tcx.symbol_name(instance).name;
+                    let is_weak = attrs.linkage == Some(Linkage::WeakAny);
                     if symbol_name == link_name.as_str() {
-                        if let Some((original_instance, original_cnum)) = instance_and_crate {
-                            // Make sure we are consistent wrt what is 'first' and 'second'.
-                            let original_span = tcx.def_span(original_instance.def_id()).data();
-                            let span = tcx.def_span(def_id).data();
-                            if original_span < span {
-                                throw_machine_stop!(TerminationInfo::MultipleSymbolDefinitions {
-                                    link_name,
-                                    first: original_span,
-                                    first_crate: tcx.crate_name(original_cnum),
-                                    second: span,
-                                    second_crate: tcx.crate_name(cnum),
-                                });
-                            } else {
-                                throw_machine_stop!(TerminationInfo::MultipleSymbolDefinitions {
-                                    link_name,
-                                    first: span,
-                                    first_crate: tcx.crate_name(cnum),
-                                    second: original_span,
-                                    second_crate: tcx.crate_name(original_cnum),
-                                });
+                        if let Some(original) = &symbol_target {
+                            // There is more than one definition with this name. What we do now
+                            // depends on whether one or both definitions are weak.
+                            match (is_weak, original.is_weak) {
+                                (false, true) => {
+                                    // Original definition is a weak definition. Override it.
+
+                                    symbol_target = Some(SymbolTarget {
+                                        instance: ty::Instance::mono(tcx, def_id),
+                                        cnum,
+                                        is_weak,
+                                    });
+                                }
+                                (true, false) => {
+                                    // Current definition is a weak definition. Keep the original one.
+                                }
+                                (true, true) | (false, false) => {
+                                    // Either both definitions are non-weak or both are weak. In
+                                    // either case return an error. For weak definitions we error
+                                    // because it is unspecified which definition would have been
+                                    // picked by the linker.
+
+                                    // Make sure we are consistent wrt what is 'first' and 'second'.
+                                    let original_span =
+                                        tcx.def_span(original.instance.def_id()).data();
+                                    let span = tcx.def_span(def_id).data();
+                                    if original_span < span {
+                                        throw_machine_stop!(
+                                            TerminationInfo::MultipleSymbolDefinitions {
+                                                link_name,
+                                                first: original_span,
+                                                first_crate: tcx.crate_name(original.cnum),
+                                                second: span,
+                                                second_crate: tcx.crate_name(cnum),
+                                            }
+                                        );
+                                    } else {
+                                        throw_machine_stop!(
+                                            TerminationInfo::MultipleSymbolDefinitions {
+                                                link_name,
+                                                first: span,
+                                                first_crate: tcx.crate_name(cnum),
+                                                second: original_span,
+                                                second_crate: tcx.crate_name(original.cnum),
+                                            }
+                                        );
+                                    }
+                                }
                             }
+                        } else {
+                            symbol_target = Some(SymbolTarget {
+                                instance: ty::Instance::mono(tcx, def_id),
+                                cnum,
+                                is_weak,
+                            });
                         }
-                        if !matches!(tcx.def_kind(def_id), DefKind::Fn | DefKind::AssocFn) {
-                            throw_ub_format!(
-                                "attempt to call an exported symbol that is not defined as a function"
-                            );
-                        }
-                        instance_and_crate = Some((ty::Instance::mono(tcx, def_id), cnum));
                     }
                     interp_ok(())
                 })?;
 
-                e.insert(instance_and_crate.map(|ic| ic.0))
+                // Once we identified the instance corresponding to the symbol, ensure
+                // it is a function. It is okay to encounter non-functions in the search above
+                // as long as the final instance we arrive at is a function.
+                if let Some(SymbolTarget { instance, .. }) = symbol_target {
+                    if !matches!(tcx.def_kind(instance.def_id()), DefKind::Fn | DefKind::AssocFn) {
+                        throw_ub_format!(
+                            "attempt to call an exported symbol that is not defined as a function"
+                        );
+                    }
+                }
+
+                e.insert(symbol_target.map(|SymbolTarget { instance, .. }| instance))
             }
         };
         match instance {
diff --git a/src/tools/miri/src/shims/native_lib/mod.rs b/src/tools/miri/src/shims/native_lib/mod.rs
index 36c18379cb863..e2a0bdbd9b408 100644
--- a/src/tools/miri/src/shims/native_lib/mod.rs
+++ b/src/tools/miri/src/shims/native_lib/mod.rs
@@ -246,7 +246,8 @@ trait EvalContextExtPriv<'tcx>: crate::MiriInterpCxExt<'tcx> {
                         let p_map = alloc.provenance();
                         for idx in overlap {
                             // If a provenance was read by the foreign code, expose it.
-                            if let Some((prov, _idx)) = p_map.get_byte(Size::from_bytes(idx), this) {
+                            if let Some((prov, _idx)) = p_map.get_byte(Size::from_bytes(idx), this)
+                            {
                                 this.expose_provenance(prov)?;
                             }
                         }
diff --git a/src/tools/miri/src/shims/unix/android/foreign_items.rs b/src/tools/miri/src/shims/unix/android/foreign_items.rs
index 04c5d28838bbd..6cb0d221fc03d 100644
--- a/src/tools/miri/src/shims/unix/android/foreign_items.rs
+++ b/src/tools/miri/src/shims/unix/android/foreign_items.rs
@@ -4,13 +4,14 @@ use rustc_span::Symbol;
 use rustc_target::callconv::FnAbi;
 
 use crate::shims::unix::android::thread::prctl;
+use crate::shims::unix::env::EvalContextExt as _;
 use crate::shims::unix::linux_like::epoll::EvalContextExt as _;
 use crate::shims::unix::linux_like::eventfd::EvalContextExt as _;
 use crate::shims::unix::linux_like::syscall::syscall;
 use crate::*;
 
-pub fn is_dyn_sym(_name: &str) -> bool {
-    false
+pub fn is_dyn_sym(name: &str) -> bool {
+    matches!(name, "gettid")
 }
 
 impl<'tcx> EvalContextExt<'tcx> for crate::MiriInterpCx<'tcx> {}
@@ -54,6 +55,12 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 this.write_scalar(errno_place.to_ref(this).to_scalar(), dest)?;
             }
 
+            "gettid" => {
+                let [] = this.check_shim_sig_lenient(abi, CanonAbi::C, link_name, args)?;
+                let result = this.unix_gettid(link_name.as_str())?;
+                this.write_scalar(result, dest)?;
+            }
+
             // Dynamically invoked syscalls
             "syscall" => syscall(this, link_name, abi, args, dest)?,
 
diff --git a/src/tools/miri/test-cargo-miri/run-test.py b/src/tools/miri/test-cargo-miri/run-test.py
index 40bfe7f845fe5..6b3b6343b8258 100755
--- a/src/tools/miri/test-cargo-miri/run-test.py
+++ b/src/tools/miri/test-cargo-miri/run-test.py
@@ -37,7 +37,7 @@ def cargo_miri(cmd, quiet = True, targets = None):
 
 def normalize_stdout(str):
     str = str.replace("src\\", "src/") # normalize paths across platforms
-    str = re.sub("finished in \\d+\\.\\d\\ds", "finished in $TIME", str) # the time keeps changing, obviously
+    str = re.sub("\\b\\d+\\.\\d+s\\b", "$TIME", str) # the time keeps changing, obviously
     return str
 
 def check_output(actual, path, name):
diff --git a/src/tools/miri/test-cargo-miri/test.default.stdout.ref b/src/tools/miri/test-cargo-miri/test.default.stdout.ref
index 2d74d82f769ba..ef092ef703bb8 100644
--- a/src/tools/miri/test-cargo-miri/test.default.stdout.ref
+++ b/src/tools/miri/test-cargo-miri/test.default.stdout.ref
@@ -14,3 +14,4 @@ running 5 tests
 .....
 test result: ok. 5 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in $TIME
 
+all doctests ran in $TIME; merged doctests compilation took $TIME
diff --git a/src/tools/miri/test-cargo-miri/test.filter.stdout.ref b/src/tools/miri/test-cargo-miri/test.filter.stdout.ref
index b68bc983276f7..071aa5691c1aa 100644
--- a/src/tools/miri/test-cargo-miri/test.filter.stdout.ref
+++ b/src/tools/miri/test-cargo-miri/test.filter.stdout.ref
@@ -15,3 +15,4 @@ running 0 tests
 
 test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 5 filtered out; finished in $TIME
 
+all doctests ran in $TIME; merged doctests compilation took $TIME
diff --git a/src/tools/miri/test-cargo-miri/test.multiple_targets.stdout.ref b/src/tools/miri/test-cargo-miri/test.multiple_targets.stdout.ref
index a376530a8cfb2..20139e9ffe621 100644
--- a/src/tools/miri/test-cargo-miri/test.multiple_targets.stdout.ref
+++ b/src/tools/miri/test-cargo-miri/test.multiple_targets.stdout.ref
@@ -25,8 +25,10 @@ running 5 tests
 .....
 test result: ok. 5 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in $TIME
 
+all doctests ran in $TIME; merged doctests compilation took $TIME
 
 running 5 tests
 .....
 test result: ok. 5 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in $TIME
 
+all doctests ran in $TIME; merged doctests compilation took $TIME
diff --git a/src/tools/miri/tests/fail/async-shared-mutable.tree.stderr b/src/tools/miri/tests/fail/async-shared-mutable.tree.stderr
index 17efb10ceb0a2..449a29088a01d 100644
--- a/src/tools/miri/tests/fail/async-shared-mutable.tree.stderr
+++ b/src/tools/miri/tests/fail/async-shared-mutable.tree.stderr
@@ -5,6 +5,7 @@ LL |             *x = 1;
    |             ^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Frozen which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/async-shared-mutable.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/alias_through_mutation.tree.stderr b/src/tools/miri/tests/fail/both_borrows/alias_through_mutation.tree.stderr
index 9e992f88f0ccb..95b7e99dedc78 100644
--- a/src/tools/miri/tests/fail/both_borrows/alias_through_mutation.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/alias_through_mutation.tree.stderr
@@ -5,6 +5,7 @@ LL |     let _val = *target_alias;
    |                ^^^^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this child read access
 help: the accessed tag <TAG> was created here, in the initial state Frozen
   --> tests/fail/both_borrows/alias_through_mutation.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/aliasing_mut1.tree.stderr b/src/tools/miri/tests/fail/both_borrows/aliasing_mut1.tree.stderr
index e331ff2406dd0..207ed3131af37 100644
--- a/src/tools/miri/tests/fail/both_borrows/aliasing_mut1.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/aliasing_mut1.tree.stderr
@@ -5,6 +5,7 @@ LL |     *x = 1;
    |     ^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Reserved (conflicted) which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/both_borrows/aliasing_mut1.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/aliasing_mut2.tree.stderr b/src/tools/miri/tests/fail/both_borrows/aliasing_mut2.tree.stderr
index a2191da0b4f68..90b1b1294c7f3 100644
--- a/src/tools/miri/tests/fail/both_borrows/aliasing_mut2.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/aliasing_mut2.tree.stderr
@@ -5,6 +5,7 @@ LL |     *y = 2;
    |     ^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Reserved (conflicted) which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/both_borrows/aliasing_mut2.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/aliasing_mut3.tree.stderr b/src/tools/miri/tests/fail/both_borrows/aliasing_mut3.tree.stderr
index e92cad1777bcc..73a5027646388 100644
--- a/src/tools/miri/tests/fail/both_borrows/aliasing_mut3.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/aliasing_mut3.tree.stderr
@@ -5,6 +5,7 @@ LL |     *x = 1;
    |     ^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Reserved (conflicted) which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/both_borrows/aliasing_mut3.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/aliasing_mut4.tree.stderr b/src/tools/miri/tests/fail/both_borrows/aliasing_mut4.tree.stderr
index e195b0a7e874e..a6a6da3fa2aec 100644
--- a/src/tools/miri/tests/fail/both_borrows/aliasing_mut4.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/aliasing_mut4.tree.stderr
@@ -5,6 +5,7 @@ LL |         crate::intrinsics::write_via_move(dest, src);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> is foreign to the protected tag <TAG> (i.e., it is not a child)
    = help: this foreign write access would cause the protected tag <TAG> (currently Frozen) to become Disabled
    = help: protected tags must never be Disabled
diff --git a/src/tools/miri/tests/fail/both_borrows/box_exclusive_violation1.tree.stderr b/src/tools/miri/tests/fail/both_borrows/box_exclusive_violation1.tree.stderr
index 30832ae60ac17..d4cfab024bae1 100644
--- a/src/tools/miri/tests/fail/both_borrows/box_exclusive_violation1.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/box_exclusive_violation1.tree.stderr
@@ -5,6 +5,7 @@ LL |         *LEAK = 7;
    |         ^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Frozen
   --> tests/fail/both_borrows/box_exclusive_violation1.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/box_noalias_violation.tree.stderr b/src/tools/miri/tests/fail/both_borrows/box_noalias_violation.tree.stderr
index d7b865d57a803..3c8ec7f7d3e4a 100644
--- a/src/tools/miri/tests/fail/both_borrows/box_noalias_violation.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/box_noalias_violation.tree.stderr
@@ -5,6 +5,7 @@ LL |     *y
    |     ^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> is foreign to the protected tag <TAG> (i.e., it is not a child)
    = help: this foreign read access would cause the protected tag <TAG> (currently Active) to become Disabled
    = help: protected tags must never be Disabled
diff --git a/src/tools/miri/tests/fail/both_borrows/buggy_as_mut_slice.tree.stderr b/src/tools/miri/tests/fail/both_borrows/buggy_as_mut_slice.tree.stderr
index ad5df3399c82e..6588bc25df13f 100644
--- a/src/tools/miri/tests/fail/both_borrows/buggy_as_mut_slice.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/buggy_as_mut_slice.tree.stderr
@@ -5,6 +5,7 @@ LL |     v2[1] = 7;
    |     ^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/both_borrows/buggy_as_mut_slice.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/buggy_split_at_mut.tree.stderr b/src/tools/miri/tests/fail/both_borrows/buggy_split_at_mut.tree.stderr
index 4ab49e75adb26..6ef27515fcd06 100644
--- a/src/tools/miri/tests/fail/both_borrows/buggy_split_at_mut.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/buggy_split_at_mut.tree.stderr
@@ -5,6 +5,7 @@ LL |     b[1] = 6;
    |     ^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/both_borrows/buggy_split_at_mut.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/illegal_write1.tree.stderr b/src/tools/miri/tests/fail/both_borrows/illegal_write1.tree.stderr
index b718e19ff5aee..4ffc7a75e66da 100644
--- a/src/tools/miri/tests/fail/both_borrows/illegal_write1.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/illegal_write1.tree.stderr
@@ -5,6 +5,7 @@ LL |         unsafe { *x = 42 };
    |                  ^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Frozen which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Frozen
   --> tests/fail/both_borrows/illegal_write1.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/illegal_write5.tree.stderr b/src/tools/miri/tests/fail/both_borrows/illegal_write5.tree.stderr
index d4c78c4bd335f..fc5b12da70e7c 100644
--- a/src/tools/miri/tests/fail/both_borrows/illegal_write5.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/illegal_write5.tree.stderr
@@ -5,6 +5,7 @@ LL |     let _val = *xref;
    |                ^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this child read access
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/both_borrows/illegal_write5.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/illegal_write6.tree.stderr b/src/tools/miri/tests/fail/both_borrows/illegal_write6.tree.stderr
index e537bc18c050d..6780e52c3baf3 100644
--- a/src/tools/miri/tests/fail/both_borrows/illegal_write6.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/illegal_write6.tree.stderr
@@ -5,6 +5,7 @@ LL |     unsafe { *y = 2 };
    |              ^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> is foreign to the protected tag <TAG> (i.e., it is not a child)
    = help: this foreign write access would cause the protected tag <TAG> (currently Active) to become Disabled
    = help: protected tags must never be Disabled
diff --git a/src/tools/miri/tests/fail/both_borrows/invalidate_against_protector2.tree.stderr b/src/tools/miri/tests/fail/both_borrows/invalidate_against_protector2.tree.stderr
index af90e75d38403..90a89e48e61bf 100644
--- a/src/tools/miri/tests/fail/both_borrows/invalidate_against_protector2.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/invalidate_against_protector2.tree.stderr
@@ -5,6 +5,7 @@ LL |     unsafe { *x = 0 };
    |              ^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> is foreign to the protected tag <TAG> (i.e., it is not a child)
    = help: this foreign write access would cause the protected tag <TAG> (currently Frozen) to become Disabled
    = help: protected tags must never be Disabled
diff --git a/src/tools/miri/tests/fail/both_borrows/invalidate_against_protector3.tree.stderr b/src/tools/miri/tests/fail/both_borrows/invalidate_against_protector3.tree.stderr
index 5d5f5e59ead7e..8bac71dcd4682 100644
--- a/src/tools/miri/tests/fail/both_borrows/invalidate_against_protector3.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/invalidate_against_protector3.tree.stderr
@@ -5,6 +5,7 @@ LL |     unsafe { *x = 0 };
    |              ^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> (root of the allocation) is foreign to the protected tag <TAG> (i.e., it is not a child)
    = help: this foreign write access would cause the protected tag <TAG> (currently Frozen) to become Disabled
    = help: protected tags must never be Disabled
diff --git a/src/tools/miri/tests/fail/both_borrows/load_invalid_shr.tree.stderr b/src/tools/miri/tests/fail/both_borrows/load_invalid_shr.tree.stderr
index 86c12603c072a..e4bde2f7aeabe 100644
--- a/src/tools/miri/tests/fail/both_borrows/load_invalid_shr.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/load_invalid_shr.tree.stderr
@@ -5,6 +5,7 @@ LL |     let _val = *xref_in_mem;
    |                ^^^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this reborrow (acting as a child read access)
 help: the accessed tag <TAG> was created here, in the initial state Frozen
   --> tests/fail/both_borrows/load_invalid_shr.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/mut_exclusive_violation1.tree.stderr b/src/tools/miri/tests/fail/both_borrows/mut_exclusive_violation1.tree.stderr
index 5f14f23e8d6b8..f5c1dea69f02b 100644
--- a/src/tools/miri/tests/fail/both_borrows/mut_exclusive_violation1.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/mut_exclusive_violation1.tree.stderr
@@ -5,6 +5,7 @@ LL |         *LEAK = 7;
    |         ^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Frozen
   --> tests/fail/both_borrows/mut_exclusive_violation1.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/mut_exclusive_violation2.tree.stderr b/src/tools/miri/tests/fail/both_borrows/mut_exclusive_violation2.tree.stderr
index edc72b0abbf01..c1b0821a9feeb 100644
--- a/src/tools/miri/tests/fail/both_borrows/mut_exclusive_violation2.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/mut_exclusive_violation2.tree.stderr
@@ -5,6 +5,7 @@ LL |         *raw1 = 3;
    |         ^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/both_borrows/mut_exclusive_violation2.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/newtype_pair_retagging.tree.stderr b/src/tools/miri/tests/fail/both_borrows/newtype_pair_retagging.tree.stderr
index 1984a6a07463b..aa07ef53b315b 100644
--- a/src/tools/miri/tests/fail/both_borrows/newtype_pair_retagging.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/newtype_pair_retagging.tree.stderr
@@ -5,6 +5,7 @@ LL |                 self.1.deallocate(From::from(ptr.cast()), layout);
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> is foreign to the protected tag <TAG> (i.e., it is not a child)
    = help: this deallocation (acting as a foreign write access) would cause the protected tag <TAG> (currently Reserved (conflicted)) to become Disabled
    = help: protected tags must never be Disabled
diff --git a/src/tools/miri/tests/fail/both_borrows/newtype_retagging.tree.stderr b/src/tools/miri/tests/fail/both_borrows/newtype_retagging.tree.stderr
index 7bd0cd14d7921..c8a72c5917620 100644
--- a/src/tools/miri/tests/fail/both_borrows/newtype_retagging.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/newtype_retagging.tree.stderr
@@ -5,6 +5,7 @@ LL |                 self.1.deallocate(From::from(ptr.cast()), layout);
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> is foreign to the protected tag <TAG> (i.e., it is not a child)
    = help: this deallocation (acting as a foreign write access) would cause the protected tag <TAG> (currently Reserved (conflicted)) to become Disabled
    = help: protected tags must never be Disabled
diff --git a/src/tools/miri/tests/fail/both_borrows/outdated_local.tree.stderr b/src/tools/miri/tests/fail/both_borrows/outdated_local.tree.stderr
index 8cb44d2635fea..5310f8b9d0995 100644
--- a/src/tools/miri/tests/fail/both_borrows/outdated_local.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/outdated_local.tree.stderr
@@ -5,6 +5,7 @@ LL |     assert_eq!(unsafe { *y }, 1);
    |                         ^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this child read access
 help: the accessed tag <TAG> was created here, in the initial state Frozen
   --> tests/fail/both_borrows/outdated_local.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/pass_invalid_shr.tree.stderr b/src/tools/miri/tests/fail/both_borrows/pass_invalid_shr.tree.stderr
index 1bd760426dac8..3c813d35031b5 100644
--- a/src/tools/miri/tests/fail/both_borrows/pass_invalid_shr.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/pass_invalid_shr.tree.stderr
@@ -5,6 +5,7 @@ LL |     foo(xref);
    |         ^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this reborrow (acting as a child read access)
 help: the accessed tag <TAG> was created here, in the initial state Frozen
   --> tests/fail/both_borrows/pass_invalid_shr.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/pass_invalid_shr_option.tree.stderr b/src/tools/miri/tests/fail/both_borrows/pass_invalid_shr_option.tree.stderr
index 2f999a8aae053..4747c65ba8353 100644
--- a/src/tools/miri/tests/fail/both_borrows/pass_invalid_shr_option.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/pass_invalid_shr_option.tree.stderr
@@ -5,6 +5,7 @@ LL |     foo(some_xref);
    |         ^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this reborrow (acting as a child read access)
 help: the accessed tag <TAG> was created here, in the initial state Frozen
   --> tests/fail/both_borrows/pass_invalid_shr_option.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/pass_invalid_shr_tuple.tree.stderr b/src/tools/miri/tests/fail/both_borrows/pass_invalid_shr_tuple.tree.stderr
index b30bda598d217..da011cfd3f74a 100644
--- a/src/tools/miri/tests/fail/both_borrows/pass_invalid_shr_tuple.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/pass_invalid_shr_tuple.tree.stderr
@@ -5,6 +5,7 @@ LL |     foo(pair_xref);
    |         ^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this reborrow (acting as a child read access)
 help: the accessed tag <TAG> was created here, in the initial state Frozen
   --> tests/fail/both_borrows/pass_invalid_shr_tuple.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/return_invalid_shr.tree.stderr b/src/tools/miri/tests/fail/both_borrows/return_invalid_shr.tree.stderr
index 2b2650a254d34..ee0f313d980da 100644
--- a/src/tools/miri/tests/fail/both_borrows/return_invalid_shr.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/return_invalid_shr.tree.stderr
@@ -5,6 +5,7 @@ LL |     ret
    |     ^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this reborrow (acting as a child read access)
 help: the accessed tag <TAG> was created here, in the initial state Frozen
   --> tests/fail/both_borrows/return_invalid_shr.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/return_invalid_shr_option.tree.stderr b/src/tools/miri/tests/fail/both_borrows/return_invalid_shr_option.tree.stderr
index b8e963f87d988..16110e5b062cc 100644
--- a/src/tools/miri/tests/fail/both_borrows/return_invalid_shr_option.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/return_invalid_shr_option.tree.stderr
@@ -5,6 +5,7 @@ LL |     ret
    |     ^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this reborrow (acting as a child read access)
 help: the accessed tag <TAG> was created here, in the initial state Frozen
   --> tests/fail/both_borrows/return_invalid_shr_option.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/return_invalid_shr_tuple.tree.stderr b/src/tools/miri/tests/fail/both_borrows/return_invalid_shr_tuple.tree.stderr
index 8e499369f08d7..f93698f570ee4 100644
--- a/src/tools/miri/tests/fail/both_borrows/return_invalid_shr_tuple.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/return_invalid_shr_tuple.tree.stderr
@@ -5,6 +5,7 @@ LL |     ret
    |     ^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this reborrow (acting as a child read access)
 help: the accessed tag <TAG> was created here, in the initial state Frozen
   --> tests/fail/both_borrows/return_invalid_shr_tuple.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/shr_frozen_violation1.tree.stderr b/src/tools/miri/tests/fail/both_borrows/shr_frozen_violation1.tree.stderr
index a28754f54127b..d9b75f65f752e 100644
--- a/src/tools/miri/tests/fail/both_borrows/shr_frozen_violation1.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/shr_frozen_violation1.tree.stderr
@@ -5,6 +5,7 @@ LL |         *(x as *const i32 as *mut i32) = 7;
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Frozen which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Frozen
   --> tests/fail/both_borrows/shr_frozen_violation1.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/shr_frozen_violation2.tree.stderr b/src/tools/miri/tests/fail/both_borrows/shr_frozen_violation2.tree.stderr
index 0eb2dc3df7701..c680c04137bc6 100644
--- a/src/tools/miri/tests/fail/both_borrows/shr_frozen_violation2.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/shr_frozen_violation2.tree.stderr
@@ -5,6 +5,7 @@ LL |         let _val = *frozen;
    |                    ^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this child read access
 help: the accessed tag <TAG> was created here, in the initial state Frozen
   --> tests/fail/both_borrows/shr_frozen_violation2.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/both_borrows/zero-sized-protected.tree.stderr b/src/tools/miri/tests/fail/both_borrows/zero-sized-protected.tree.stderr
index 2a9a9afb0f0c8..66a7d7794e968 100644
--- a/src/tools/miri/tests/fail/both_borrows/zero-sized-protected.tree.stderr
+++ b/src/tools/miri/tests/fail/both_borrows/zero-sized-protected.tree.stderr
@@ -5,6 +5,7 @@ LL |     unsafe { dealloc(ptr, l) };
    |              ^^^^^^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the allocation of the accessed tag <TAG> (root of the allocation) also contains the strongly protected tag <TAG>
    = help: the strongly protected tag <TAG> disallows deallocations
 help: the accessed tag <TAG> was created here
diff --git a/src/tools/miri/tests/fail/function_calls/arg_inplace_locals_alias.tree.stderr b/src/tools/miri/tests/fail/function_calls/arg_inplace_locals_alias.tree.stderr
index f376c30c87927..2266a9c39f91d 100644
--- a/src/tools/miri/tests/fail/function_calls/arg_inplace_locals_alias.tree.stderr
+++ b/src/tools/miri/tests/fail/function_calls/arg_inplace_locals_alias.tree.stderr
@@ -5,6 +5,7 @@ LL |             Call(_unit = callee(Move(non_copy), Move(non_copy)), ReturnTo(a
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> (root of the allocation) is foreign to the protected tag <TAG> (i.e., it is not a child)
    = help: this foreign read access would cause the protected tag <TAG> (currently Active) to become Disabled
    = help: protected tags must never be Disabled
diff --git a/src/tools/miri/tests/fail/function_calls/arg_inplace_mutate.tree.stderr b/src/tools/miri/tests/fail/function_calls/arg_inplace_mutate.tree.stderr
index 2f1dc1988f570..1995528e9f9df 100644
--- a/src/tools/miri/tests/fail/function_calls/arg_inplace_mutate.tree.stderr
+++ b/src/tools/miri/tests/fail/function_calls/arg_inplace_mutate.tree.stderr
@@ -5,6 +5,7 @@ LL |     unsafe { ptr.write(S(0)) };
    |              ^^^^^^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> (root of the allocation) is foreign to the protected tag <TAG> (i.e., it is not a child)
    = help: this foreign write access would cause the protected tag <TAG> (currently Active) to become Disabled
    = help: protected tags must never be Disabled
diff --git a/src/tools/miri/tests/fail/function_calls/arg_inplace_observe_during.tree.stderr b/src/tools/miri/tests/fail/function_calls/arg_inplace_observe_during.tree.stderr
index 5db5a6cac4d14..e506a61c6bb3b 100644
--- a/src/tools/miri/tests/fail/function_calls/arg_inplace_observe_during.tree.stderr
+++ b/src/tools/miri/tests/fail/function_calls/arg_inplace_observe_during.tree.stderr
@@ -5,6 +5,7 @@ LL |     unsafe { ptr.read() };
    |              ^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> (root of the allocation) is foreign to the protected tag <TAG> (i.e., it is not a child)
    = help: this foreign read access would cause the protected tag <TAG> (currently Active) to become Disabled
    = help: protected tags must never be Disabled
diff --git a/src/tools/miri/tests/fail/function_calls/return_pointer_aliasing_read.tree.stderr b/src/tools/miri/tests/fail/function_calls/return_pointer_aliasing_read.tree.stderr
index a1cf0b730eba1..b1aa2ba28860c 100644
--- a/src/tools/miri/tests/fail/function_calls/return_pointer_aliasing_read.tree.stderr
+++ b/src/tools/miri/tests/fail/function_calls/return_pointer_aliasing_read.tree.stderr
@@ -5,6 +5,7 @@ LL |     unsafe { ptr.read() };
    |              ^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> (root of the allocation) is foreign to the protected tag <TAG> (i.e., it is not a child)
    = help: this foreign read access would cause the protected tag <TAG> (currently Active) to become Disabled
    = help: protected tags must never be Disabled
diff --git a/src/tools/miri/tests/fail/function_calls/return_pointer_aliasing_write.tree.stderr b/src/tools/miri/tests/fail/function_calls/return_pointer_aliasing_write.tree.stderr
index 01d15f38af6df..0cf449ea3ec2f 100644
--- a/src/tools/miri/tests/fail/function_calls/return_pointer_aliasing_write.tree.stderr
+++ b/src/tools/miri/tests/fail/function_calls/return_pointer_aliasing_write.tree.stderr
@@ -5,6 +5,7 @@ LL |     unsafe { ptr.write(0) };
    |              ^^^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> (root of the allocation) is foreign to the protected tag <TAG> (i.e., it is not a child)
    = help: this foreign write access would cause the protected tag <TAG> (currently Active) to become Disabled
    = help: protected tags must never be Disabled
diff --git a/src/tools/miri/tests/fail/function_calls/return_pointer_aliasing_write_tail_call.tree.stderr b/src/tools/miri/tests/fail/function_calls/return_pointer_aliasing_write_tail_call.tree.stderr
index 812ddb94a735b..a006c6feae43c 100644
--- a/src/tools/miri/tests/fail/function_calls/return_pointer_aliasing_write_tail_call.tree.stderr
+++ b/src/tools/miri/tests/fail/function_calls/return_pointer_aliasing_write_tail_call.tree.stderr
@@ -5,6 +5,7 @@ LL |     unsafe { ptr.write(0) };
    |              ^^^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> (root of the allocation) is foreign to the protected tag <TAG> (i.e., it is not a child)
    = help: this foreign write access would cause the protected tag <TAG> (currently Active) to become Disabled
    = help: protected tags must never be Disabled
diff --git a/src/tools/miri/tests/fail/tree_borrows/alternate-read-write.stderr b/src/tools/miri/tests/fail/tree_borrows/alternate-read-write.stderr
index 63c6287f20d45..9e955a6d5b196 100644
--- a/src/tools/miri/tests/fail/tree_borrows/alternate-read-write.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/alternate-read-write.stderr
@@ -5,6 +5,7 @@ LL |     *y += 1; // Failure
    |     ^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Frozen which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/tree_borrows/alternate-read-write.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/tree_borrows/cell-inside-struct.stderr b/src/tools/miri/tests/fail/tree_borrows/cell-inside-struct.stderr
index 81d5aba6b2ec3..5e43d174ed902 100644
--- a/src/tools/miri/tests/fail/tree_borrows/cell-inside-struct.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/cell-inside-struct.stderr
@@ -11,6 +11,7 @@ LL |         (*a).field1 = 88;
    |         ^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> (a) has state Frozen which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Cell
   --> tests/fail/tree_borrows/cell-inside-struct.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/tree_borrows/error-range.stderr b/src/tools/miri/tests/fail/tree_borrows/error-range.stderr
index 9a52f68d9b65d..3dc120a20d23e 100644
--- a/src/tools/miri/tests/fail/tree_borrows/error-range.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/error-range.stderr
@@ -5,6 +5,7 @@ LL |         rmut[5] += 1;
    |         ^^^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this child read access
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/tree_borrows/error-range.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/tree_borrows/fnentry_invalidation.stderr b/src/tools/miri/tests/fail/tree_borrows/fnentry_invalidation.stderr
index ed345aae38f1c..7886029dccfc2 100644
--- a/src/tools/miri/tests/fail/tree_borrows/fnentry_invalidation.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/fnentry_invalidation.stderr
@@ -5,6 +5,7 @@ LL |         *z = 2;
    |         ^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Frozen which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/tree_borrows/fnentry_invalidation.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/tree_borrows/outside-range.stderr b/src/tools/miri/tests/fail/tree_borrows/outside-range.stderr
index bbd33dc356093..7960f42faa519 100644
--- a/src/tools/miri/tests/fail/tree_borrows/outside-range.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/outside-range.stderr
@@ -5,6 +5,7 @@ LL |     *y.add(3) = 42;
    |     ^^^^^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> is foreign to the protected tag <TAG> (i.e., it is not a child)
    = help: this foreign write access would cause the protected tag <TAG> (currently Reserved) to become Disabled
    = help: protected tags must never be Disabled
diff --git a/src/tools/miri/tests/fail/tree_borrows/parent_read_freezes_raw_mut.stderr b/src/tools/miri/tests/fail/tree_borrows/parent_read_freezes_raw_mut.stderr
index a4119bc017858..2edbbd80569b2 100644
--- a/src/tools/miri/tests/fail/tree_borrows/parent_read_freezes_raw_mut.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/parent_read_freezes_raw_mut.stderr
@@ -5,6 +5,7 @@ LL |         *ptr = 0;
    |         ^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Frozen which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/tree_borrows/parent_read_freezes_raw_mut.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/tree_borrows/pass_invalid_mut.stderr b/src/tools/miri/tests/fail/tree_borrows/pass_invalid_mut.stderr
index de01a9f0e80fe..c00c67173b7d8 100644
--- a/src/tools/miri/tests/fail/tree_borrows/pass_invalid_mut.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/pass_invalid_mut.stderr
@@ -5,6 +5,7 @@ LL |     *nope = 31;
    |     ^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> is a child of the conflicting tag <TAG>
    = help: the conflicting tag <TAG> has state Frozen which forbids this child write access
 help: the accessed tag <TAG> was created here
diff --git a/src/tools/miri/tests/fail/tree_borrows/protector-write-lazy.stderr b/src/tools/miri/tests/fail/tree_borrows/protector-write-lazy.stderr
index af226b9e3be47..7cebd7f32a0ac 100644
--- a/src/tools/miri/tests/fail/tree_borrows/protector-write-lazy.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/protector-write-lazy.stderr
@@ -5,6 +5,7 @@ LL |     unsafe { println!("Value of funky: {}", *funky_ptr_lazy_on_fst_elem) }
    |                                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this reborrow (acting as a child read access)
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/tree_borrows/protector-write-lazy.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/tree_borrows/repeated_foreign_read_lazy_conflicted.stderr b/src/tools/miri/tests/fail/tree_borrows/repeated_foreign_read_lazy_conflicted.stderr
index 8421df5ab7992..012d7caef501a 100644
--- a/src/tools/miri/tests/fail/tree_borrows/repeated_foreign_read_lazy_conflicted.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/repeated_foreign_read_lazy_conflicted.stderr
@@ -5,6 +5,7 @@ LL |     *(x as *mut u8).byte_sub(1) = 42;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Reserved (conflicted) which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/tree_borrows/repeated_foreign_read_lazy_conflicted.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/tree_borrows/reserved/cell-protected-write.stderr b/src/tools/miri/tests/fail/tree_borrows/reserved/cell-protected-write.stderr
index 00d5c3e6b67b4..b1c3ffe86ef7f 100644
--- a/src/tools/miri/tests/fail/tree_borrows/reserved/cell-protected-write.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/reserved/cell-protected-write.stderr
@@ -15,6 +15,7 @@ LL |             *y = 1;
    |             ^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> (y, callee:y, caller:y) is foreign to the protected tag <TAG> (callee:x) (i.e., it is not a child)
    = help: this foreign write access would cause the protected tag <TAG> (callee:x) (currently Reserved) to become Disabled
    = help: protected tags must never be Disabled
diff --git a/src/tools/miri/tests/fail/tree_borrows/reserved/int-protected-write.stderr b/src/tools/miri/tests/fail/tree_borrows/reserved/int-protected-write.stderr
index c003938db336e..5f3129b9dc089 100644
--- a/src/tools/miri/tests/fail/tree_borrows/reserved/int-protected-write.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/reserved/int-protected-write.stderr
@@ -15,6 +15,7 @@ LL |             *y = 0;
    |             ^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> (y, callee:y, caller:y) is foreign to the protected tag <TAG> (callee:x) (i.e., it is not a child)
    = help: this foreign write access would cause the protected tag <TAG> (callee:x) (currently Reserved) to become Disabled
    = help: protected tags must never be Disabled
diff --git a/src/tools/miri/tests/fail/tree_borrows/reservedim_spurious_write.with.stderr b/src/tools/miri/tests/fail/tree_borrows/reservedim_spurious_write.with.stderr
index a8db707033350..7565fa6203f97 100644
--- a/src/tools/miri/tests/fail/tree_borrows/reservedim_spurious_write.with.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/reservedim_spurious_write.with.stderr
@@ -19,6 +19,7 @@ LL |         unsafe { *y = 13 }
    |                  ^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/tree_borrows/reservedim_spurious_write.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/tree_borrows/reservedim_spurious_write.without.stderr b/src/tools/miri/tests/fail/tree_borrows/reservedim_spurious_write.without.stderr
index 5eeefd450c62c..7f791c88dde38 100644
--- a/src/tools/miri/tests/fail/tree_borrows/reservedim_spurious_write.without.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/reservedim_spurious_write.without.stderr
@@ -19,6 +19,7 @@ LL |         unsafe { *y = 13 }
    |                  ^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/tree_borrows/reservedim_spurious_write.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/tree_borrows/return_invalid_mut.stderr b/src/tools/miri/tests/fail/tree_borrows/return_invalid_mut.stderr
index a0ebf0ecbd26f..ba8ab472872f7 100644
--- a/src/tools/miri/tests/fail/tree_borrows/return_invalid_mut.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/return_invalid_mut.stderr
@@ -5,6 +5,7 @@ LL |     *ret = 3;
    |     ^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> is a child of the conflicting tag <TAG>
    = help: the conflicting tag <TAG> has state Frozen which forbids this child write access
 help: the accessed tag <TAG> was created here
diff --git a/src/tools/miri/tests/fail/tree_borrows/spurious_read.stderr b/src/tools/miri/tests/fail/tree_borrows/spurious_read.stderr
index a3b0d5f13ad3c..8f2534d6b6e97 100644
--- a/src/tools/miri/tests/fail/tree_borrows/spurious_read.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/spurious_read.stderr
@@ -18,6 +18,7 @@ LL |                 *y = 2;
    |                 ^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Reserved (conflicted) which forbids this child write access
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/tree_borrows/spurious_read.rs:LL:CC
diff --git a/src/tools/miri/tests/fail/tree_borrows/strongly-protected.stderr b/src/tools/miri/tests/fail/tree_borrows/strongly-protected.stderr
index 56617f6d6a6ab..685abee3292f6 100644
--- a/src/tools/miri/tests/fail/tree_borrows/strongly-protected.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/strongly-protected.stderr
@@ -5,6 +5,7 @@ LL |                 self.1.deallocate(From::from(ptr.cast()), layout);
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the allocation of the accessed tag <TAG> also contains the strongly protected tag <TAG>
    = help: the strongly protected tag <TAG> disallows deallocations
 help: the accessed tag <TAG> was created here
diff --git a/src/tools/miri/tests/fail/tree_borrows/subtree_traversal_skipping_diagnostics.stderr b/src/tools/miri/tests/fail/tree_borrows/subtree_traversal_skipping_diagnostics.stderr
index 8669a14ecc712..b98d2fafcf4ee 100644
--- a/src/tools/miri/tests/fail/tree_borrows/subtree_traversal_skipping_diagnostics.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/subtree_traversal_skipping_diagnostics.stderr
@@ -5,6 +5,7 @@ LL |     *m = 42;
    |     ^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> is a child of the conflicting tag <TAG>
    = help: the conflicting tag <TAG> has state Frozen which forbids this child write access
 help: the accessed tag <TAG> was created here
diff --git a/src/tools/miri/tests/fail/tree_borrows/write-during-2phase.stderr b/src/tools/miri/tests/fail/tree_borrows/write-during-2phase.stderr
index 693d18535502d..7f55e06a6bb7a 100644
--- a/src/tools/miri/tests/fail/tree_borrows/write-during-2phase.stderr
+++ b/src/tools/miri/tests/fail/tree_borrows/write-during-2phase.stderr
@@ -5,6 +5,7 @@ LL |     fn add(&mut self, n: u64) -> u64 {
    |            ^^^^^^^^^ Undefined Behavior occurred here
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
+   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
    = help: the accessed tag <TAG> has state Disabled which forbids this reborrow (acting as a child read access)
 help: the accessed tag <TAG> was created here, in the initial state Reserved
   --> tests/fail/tree_borrows/write-during-2phase.rs:LL:CC
diff --git a/src/tools/miri/tests/pass/function_calls/exported_symbol_weak.rs b/src/tools/miri/tests/pass/function_calls/exported_symbol_weak.rs
new file mode 100644
index 0000000000000..abf4b6718ab26
--- /dev/null
+++ b/src/tools/miri/tests/pass/function_calls/exported_symbol_weak.rs
@@ -0,0 +1,39 @@
+#![feature(linkage)]
+
+// FIXME move this module to a separate crate once aux-build is allowed
+// This currently depends on the fact that miri skips the codegen check
+// that denies multiple symbols with the same name.
+mod first {
+    #[no_mangle]
+    #[linkage = "weak"]
+    extern "C" fn foo() -> i32 {
+        1
+    }
+
+    #[no_mangle]
+    #[linkage = "weak"]
+    extern "C" fn bar() -> i32 {
+        2
+    }
+}
+
+mod second {
+    #[no_mangle]
+    extern "C" fn bar() -> i32 {
+        3
+    }
+}
+
+extern "C" {
+    fn foo() -> i32;
+    fn bar() -> i32;
+}
+
+fn main() {
+    unsafe {
+        // If there is no non-weak definition, the weak definition will be used.
+        assert_eq!(foo(), 1);
+        // Non-weak definition takes presedence.
+        assert_eq!(bar(), 3);
+    }
+}
diff --git a/src/tools/miri/triagebot.toml b/src/tools/miri/triagebot.toml
index a0ce9f800242f..c747cbb0a5211 100644
--- a/src/tools/miri/triagebot.toml
+++ b/src/tools/miri/triagebot.toml
@@ -50,11 +50,14 @@ new_pr = true
 [autolabel."S-waiting-on-author"]
 new_draft = true
 
-# Automatically close and reopen PRs made by bots to run CI on them
-[bot-pull-requests]
-
-# Canonicalize issue numbers to avoid closing the wrong issue when upstreaming this subtree
+# Canonicalize issue numbers to avoid closing the wrong issue when upstreaming this subtree.
 [canonicalize-issue-links]
 
-# Prevents mentions in commits to avoid users being spammed
+# Prevents mentions in commits to avoid users being spammed.
 [no-mentions]
+
+# Show range-diff links on force pushes.
+[range-diff]
+
+# Add link to the review body to review changes since posting it.
+[review-changes-since]
diff --git a/tests/ui/explicit-tail-calls/ret-ty-hr-mismatch.rs b/tests/ui/explicit-tail-calls/ret-ty-hr-mismatch.rs
new file mode 100644
index 0000000000000..8ad244568a3ee
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/ret-ty-hr-mismatch.rs
@@ -0,0 +1,15 @@
+#![feature(explicit_tail_calls)]
+#![expect(incomplete_features)]
+
+fn foo() -> for<'a> fn(&'a i32) {
+    become bar();
+    //~^ ERROR mismatched signatures
+}
+
+fn bar() -> fn(&'static i32) {
+    dummy
+}
+
+fn dummy(_: &i32) {}
+
+fn main() {}
diff --git a/tests/ui/explicit-tail-calls/ret-ty-hr-mismatch.stderr b/tests/ui/explicit-tail-calls/ret-ty-hr-mismatch.stderr
new file mode 100644
index 0000000000000..f6594580ba52d
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/ret-ty-hr-mismatch.stderr
@@ -0,0 +1,12 @@
+error: mismatched signatures
+  --> $DIR/ret-ty-hr-mismatch.rs:5:5
+   |
+LL |     become bar();
+   |     ^^^^^^^^^^^^
+   |
+   = note: `become` requires caller and callee to have matching signatures
+   = note: caller signature: `fn() -> for<'a> fn(&'a i32)`
+   = note: callee signature: `fn() -> fn(&'static i32)`
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/explicit-tail-calls/ret-ty-modulo-anonymization.rs b/tests/ui/explicit-tail-calls/ret-ty-modulo-anonymization.rs
new file mode 100644
index 0000000000000..0cd4e204278ac
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/ret-ty-modulo-anonymization.rs
@@ -0,0 +1,16 @@
+// Ensure that we anonymize the output of a function for tail call signature compatibility.
+
+//@ check-pass
+
+#![feature(explicit_tail_calls)]
+#![expect(incomplete_features)]
+
+fn foo() -> for<'a> fn(&'a ()) {
+    become bar();
+}
+
+fn bar() -> for<'b> fn(&'b ()) {
+    todo!()
+}
+
+fn main() {}