[lldb] Change Module to have a concrete UnwindTable, update (#101130) #9121
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
) Currently a Module has a std::optional<UnwindTable> which is created when the UnwindTable is requested from outside the Module. The idea is to delay its creation until the Module has an ObjectFile initialized, which will have been done by the time we're doing an unwind. However, Module::GetUnwindTable wasn't doing any locking, so it was possible for two threads to ask for the UnwindTable for the first time, one would be created and returned while another thread would create one, destroy the first in the process of emplacing it. It was an uncommon crash, but it was possible. Grabbing the Module's mutex would be one way to address it, but when loading ELF binaries, we start creating the SymbolTable on one thread (ObjectFileELF) grabbing the Module's mutex, and then spin up worker threads to parse the individual DWARF compilation units, which then try to also get the UnwindTable and deadlock if they try to get the Module's mutex. This changes Module to have a concrete UnwindTable as an ivar, and when it adds an ObjectFile or SymbolFileVendor, it will call the Update method on it, which will re-evaluate which sections exist in the ObjectFile/SymbolFile. UnwindTable used to have an Initialize method which set all the sections, and an Update method which would set some of them if they weren't set. I unified these with the Initialize method taking a `force` option to re-initialize the section pointers even if they had been done already before. This is addressing a rare crash report we've received, and also a failure Adrian spotted on the -fsanitize=address CI bot last week, it's still uncommon with ASAN but it can happen with the standard testsuite. rdar://128876433 (cherry picked from commit 7ad073a)
|
@swift-ci test |
JDevlieghere
approved these changes
Aug 16, 2024
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.
Currently a Module has a std::optional which is created when the UnwindTable is requested from outside the Module. The idea is to delay its creation until the Module has an ObjectFile initialized, which will have been done by the time we're doing an unwind.
However, Module::GetUnwindTable wasn't doing any locking, so it was possible for two threads to ask for the UnwindTable for the first time, one would be created and returned while another thread would create one, destroy the first in the process of emplacing it. It was an uncommon crash, but it was possible.
Grabbing the Module's mutex would be one way to address it, but when loading ELF binaries, we start creating the SymbolTable on one thread (ObjectFileELF) grabbing the Module's mutex, and then spin up worker threads to parse the individual DWARF compilation units, which then try to also get the UnwindTable and deadlock if they try to get the Module's mutex.
This changes Module to have a concrete UnwindTable as an ivar, and when it adds an ObjectFile or SymbolFileVendor, it will call the Update method on it, which will re-evaluate which sections exist in the ObjectFile/SymbolFile. UnwindTable used to have an Initialize method which set all the sections, and an Update method which would set some of them if they weren't set. I unified these with the Initialize method taking a
forceoption to re-initialize the section pointers even if they had been done already before.This is addressing a rare crash report we've received, and also a failure Adrian spotted on the -fsanitize=address CI bot last week, it's still uncommon with ASAN but it can happen with the standard testsuite.
rdar://128876433
(cherry picked from commit 7ad073a)