[AArch64] Add workaround to stack tagging (memtag) pass for Swift lldb memset #11846
+89
−2
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
In Swift codegen, allocas are memset to zero before their lifetime.start. This is done so that lldb can display a friendly 'var is uninitialized' message rather than displaying garbage. The stack-tagging pass results in this memset using the tagged pointer, before the memory has been tagged - resulting in a tag fault. This patch works around this by detecting when one of these memsets is present (using metadata added during Swift codegen), and moving the tagging after. This results in the memset using the untagged pointer, before the memory is tagged. rdar://162206592
DanBlackwell
requested review from
ndrewh,
thetruestblue,
usama54321,
wrotki and
yln
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
In Swift codegen, allocas are memset to zero before their lifetime.start. This is done so that lldb can display a friendly 'var is uninitialized' message rather than displaying garbage. The stack-tagging pass results in this memset using the tagged pointer, before the memory has been tagged - resulting in a tag fault.
This patch works around this by detecting when one of these memsets is present (using metadata added during Swift codegen), and moving the tagging after. This results in the memset using the untagged pointer, before the memory is tagged.
Paired with: swiftlang/swift#85558.
rdar://162206592