[x86_64][windows][swift] do not use Swift async extended frame for wi… #8123
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
llvm#80468) …ndows x86_64 targets that use windows 64 prologue Windows x86_64 stack frame layout is currently not compatible with Swift's async extended frame, which reserves the slot right below RBP (RBP-8) for the async context pointer, as it doesn't account for the fact that a stack object in a win64 frame can be allocated at the same location. This can cause issues at runtime, for instance, Swift's TCA test code has functions that fail because of this issue, as they spill a value to that slack slot, which then gets overwritten by a store into address returned by the @llvm.swift.async.context.addr() intrinsic (that ends up being RBP - 8), leading to an incorrect value being used at a later point when that stack slot is being read from again. This change drops the use of async extended frame for windows x86_64 subtargets and instead uses the x32 based approach of allocating a separate stack slot for the stored async context pointer. Additionally, LLDB which is the primary consumer of the extended frame makes assumptions like checking for a saved previous frame pointer at the current frame pointer address, which is also incompatible with the windows x86_64 frame layout, as the previous frame pointer is not guaranteed to be stored at the current frame pointer address. Therefore the extended frame layout can be turned off to fix the current miscompile without introducing regression into LLDB for windows x86_64 as it already doesn't work correctly. I am still investigating what should be made for LLDB to support using an allocated stack slot to store the async frame context instead of being located at RBP - 8 for windows.
|
@swift-ci please test |
compnerd
approved these changes
Feb 5, 2024
|
Yes, it's a cherry-pick, the upstream change has been merged. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
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.
…… (llvm#80468)
…ndows x86_64
targets that use windows 64 prologue
Windows x86_64 stack frame layout is currently not compatible with Swift's async extended frame, which reserves the slot right below RBP (RBP-8) for the async context pointer, as it doesn't account for the fact that a stack object in a win64 frame can be allocated at the same location. This can cause issues at runtime, for instance, Swift's TCA test code has functions that fail because of this issue, as they spill a value to that slack slot, which then gets overwritten by a store into address returned by the @llvm.swift.async.context.addr() intrinsic (that ends up being RBP - 8), leading to an incorrect value being used at a later point when that stack slot is being read from again. This change drops the use of async extended frame for windows x86_64 subtargets and instead uses the x32 based approach of allocating a separate stack slot for the stored async context pointer.
Additionally, LLDB which is the primary consumer of the extended frame makes assumptions like checking for a saved previous frame pointer at the current frame pointer address, which is also incompatible with the windows x86_64 frame layout, as the previous frame pointer is not guaranteed to be stored at the current frame pointer address. Therefore the extended frame layout can be turned off to fix the current miscompile without introducing regression into LLDB for windows x86_64 as it already doesn't work correctly. I am still investigating what should be made for LLDB to support using an allocated stack slot to store the async frame context instead of being located at RBP - 8 for windows.