merge the sgx/fortanix __rust_probestack into the general x86_64 one

Author: folkertdev

library/compiler-builtins/compiler-builtins/src/probestack.rs

@@ -56,15 +56,31 @@
 //
 // The ABI here is that the stack frame size is located in `%rax`. Upon
 // return we're not supposed to modify `%rsp` or `%rax`.
-//
-// Any changes to this function should be replicated to the SGX version below.
-#[cfg(all(
-    target_arch = "x86_64",
-    not(all(target_env = "sgx", target_vendor = "fortanix"))
-))]
+#[cfg(target_arch = "x86_64")]
 #[unsafe(naked)]
 #[rustc_std_internal_symbol]
 pub unsafe extern "C" fn __rust_probestack() {
+    #[cfg(not(all(target_env = "sgx", target_vendor = "fortanix")))]
+    macro_rules! ret {
+        () => {
+            "ret"
+        };
+    }
+
+    #[cfg(all(target_env = "sgx", target_vendor = "fortanix"))]
+    macro_rules! ret {
+        // for this target, [manually patch for LVI].
+        //
+        // [manually patch for LVI]: https://software.intel.com/security-software-guidance/insights/deep-dive-load-value-injection#specialinstructions
+        () => {
+            "
+            pop %r11
+            lfence
+            jmp *%r11
+            "
+        };
+    }
+
     core::arch::naked_asm!(
         "
     .cfi_startproc
@@ -113,75 +129,9 @@ pub unsafe extern "C" fn __rust_probestack() {
     leave
     .cfi_def_cfa_register %rsp
     .cfi_adjust_cfa_offset -8
-    ret
-    .cfi_endproc
     ",
-        options(att_syntax)
-    )
-}
-
-// This function is the same as above, except that some instructions are
-// [manually patched for LVI].
-//
-// [manually patched for LVI]: https://software.intel.com/security-software-guidance/insights/deep-dive-load-value-injection#specialinstructions
-#[cfg(all(
-    target_arch = "x86_64",
-    all(target_env = "sgx", target_vendor = "fortanix")
-))]
-#[unsafe(naked)]
-#[no_mangle]
-pub unsafe extern "C" fn __rust_probestack() {
-    core::arch::naked_asm!(
+        ret!(),
         "
-    .cfi_startproc
-    pushq  %rbp
-    .cfi_adjust_cfa_offset 8
-    .cfi_offset %rbp, -16
-    movq   %rsp, %rbp
-    .cfi_def_cfa_register %rbp
-
-    mov    %rax,%r11        // duplicate %rax as we're clobbering %r11
-
-    // Main loop, taken in one page increments. We're decrementing rsp by
-    // a page each time until there's less than a page remaining. We're
-    // guaranteed that this function isn't called unless there's more than a
-    // page needed.
-    //
-    // Note that we're also testing against `8(%rsp)` to account for the 8
-    // bytes pushed on the stack orginally with our return address. Using
-    // `8(%rsp)` simulates us testing the stack pointer in the caller's
-    // context.
-
-    // It's usually called when %rax >= 0x1000, but that's not always true.
-    // Dynamic stack allocation, which is needed to implement unsized
-    // rvalues, triggers stackprobe even if %rax < 0x1000.
-    // Thus we have to check %r11 first to avoid segfault.
-    cmp    $0x1000,%r11
-    jna    3f
-2:
-    sub    $0x1000,%rsp
-    test   %rsp,8(%rsp)
-    sub    $0x1000,%r11
-    cmp    $0x1000,%r11
-    ja     2b
-
-3:
-    // Finish up the last remaining stack space requested, getting the last
-    // bits out of r11
-    sub    %r11,%rsp
-    test   %rsp,8(%rsp)
-
-    // Restore the stack pointer to what it previously was when entering
-    // this function. The caller will readjust the stack pointer after we
-    // return.
-    add    %rax,%rsp
-
-    leave
-    .cfi_def_cfa_register %rsp
-    .cfi_adjust_cfa_offset -8
-    pop %r11
-    lfence
-    jmp *%r11
     .cfi_endproc
     ",
         options(att_syntax)