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Generic-asan.cmake

Differential D119410

[libc++][NFC] Work around false positive ODR violations from ASan.
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Authored by var-const on Feb 9 2022, 11:07 PM.

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ldionne

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rG10953974ed6b: [libc++][NFC] Work around false positive ODR violations from ASan.

Summary

This works around a known issue in ASan. ASan doesn't instrument weak
symbols. Because instrumentation increases object size, the binary can
end up with two versions of the same object, one instrumented and one
not instrumented, with different sizes, which ASan will report as an ODR
violation. In libc++, this affects typeinfo for std::bad_function_call
which is emitted as a weak symbol in the test executable and as a strong
symbol in the shared library.

The main open issue for ASan appears to be
https://github.com/google/sanitizers/issues/1017.

Diff Detail

Repository: rG LLVM Github Monorepo

Event Timeline

var-const created this revision.Feb 9 2022, 11:07 PM

Herald added a subscriber: arichardson. · View Herald TranscriptFeb 9 2022, 11:07 PM

var-const requested review of this revision.Feb 9 2022, 11:07 PM

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Harbormaster completed remote builds in B148663: Diff 407400.Feb 10 2022, 12:25 AM

@nikic @kstoimenov Any idea why this started happening between LLVM 13 and LLVM 14? We didn't have this issue before, and it started popping up a couple of days ago when we updated our Docker image. Sorry for pinging out of the blue, but you folks seem to have recent ASAN commits so maybe you're aware of a change that could cause this?

I'd like to avoid carrying hacks like this around, especially if virtually anyone using ASAN needs to do this. In that case, it would seem better to just make that the default ASAN behavior?

libcxx/utils/ci/run-buildbot
314 ↗	(On Diff #407400)	Can you move this to the `Generic-asan.cmake` cache instead?

Move flags to the cache.

Herald added a subscriber: mgorny. · View Herald TranscriptFeb 10 2022, 12:13 PM

var-const added inline comments.Feb 10 2022, 12:13 PM

libcxx/utils/ci/run-buildbot
314 ↗	(On Diff #407400)	Done (please let me know if this is what you had in mind).

I think that should work. If the ASAN bot is happy, can you please add a comment about this being "hopefully temporary" and then commit this?

Thanks for looking into it!

This revision is now accepted and ready to land.Feb 10 2022, 1:44 PM

Add comment.

Harbormaster completed remote builds in B148884: Diff 407731.Feb 11 2022, 1:15 AM

ldionne accepted this revision.Feb 11 2022, 6:57 AM

This revision was landed with ongoing or failed builds.Feb 11 2022, 11:57 AM

Closed by commit rG10953974ed6b: [libc++][NFC] Work around false positive ODR violations from ASan. (authored by var-const). · Explain Why

This revision was automatically updated to reflect the committed changes.

var-const added a commit: rG10953974ed6b: [libc++][NFC] Work around false positive ODR violations from ASan..

Merging this now. generic-asan is green on the CI and the Windows failures look unrelated ("No space left on device").

Revision Contents

Path

Size

libcxx/

cmake/

caches/

Generic-asan.cmake

2 lines

Diff 407975

libcxx/cmake/caches/Generic-asan.cmake

	set(LLVM_USE_SANITIZER "Address" CACHE STRING "")			set(LLVM_USE_SANITIZER "Address" CACHE STRING "")
				# This is a temporary (hopefully) workaround for an ASan issue (see https://llvm.org/D119410).
				set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -mllvm -asan-use-private-alias=1" CACHE INTERNAL "")