[7.0 Regression] libc++abi incorrectly aligns exceptions in 32 bit builds

[llvmbot]

Bugzilla Link	39051
Resolution	FIXED
Resolved on	Oct 22, 2018 09:29
Version	7.0
OS	Linux
Blocks	#38454
Reporter	LLVM Bugzilla Contributor
CC	@zmodem,@ldionne,@mclow,@tstellar
Fixed by commit(s)	r342815 r344917

Extended Description

Libc++ commit r339431 moved the _LIBCPP_HAS_NO_ALIGNED_ALLOCATION logic from to <__config>. As a result, it was defined when building libc++abi's fallback_malloc.cpp, which made libc++abi think posix_memalign was unavailable.

This meant that libc++abi was silently falling back to using malloc. In 32 bit builds, malloc does not return correctly aligned memory for the exception header.

This is a regression in the 7.0 release.

The issues was fixed in libc++abi commit r342815. This change should be merged into the 7.1 release.

@​Marshall, Louis, can you sign off on this?

[ldionne]

Signed off. How did you discover the bug? We should have testers for this, no?

[llvmbot]

How did you discover the bug? We should have testers for this, no?

We do. The libc++abi 32 bit buildbot has been failing for months due to this bug [1].

I suspect it's also the cause of #37821 .

[1] http://lab.llvm.org:8011/builders/libcxx-libcxxabi-x86_64-linux-ubuntu-32bit/builds/424

[ldionne]

How did you discover the bug? We should have testers for this, no?
We do. The libc++abi 32 bit buildbot has been failing for months due to this bug [1].

How embarrassing -- that one's on me.

I suspect it's also the cause of #37821 .

I don't think so: my reproduction for #37821 still fails after applying your patch.

[llvmbot]

I suspect it's also the cause of #37821 .

I don't think so: my reproduction for #37821 still fails after applying your patch.

Yeah, looking further, I think the analysis about the separate unwind headers on that bug seems correct.

[tstellar]

Marshall, is this OK to merge?

[mclow]

Marshall, is this OK to merge?

Yes; this is OK to merge for 7.1

[mclow]

Is there any reason that this bug should not be closed?

[llvmbot]

Have we merged the commit? That would be the reason to keep this open.

[ldionne]

I don't think the commit has been merged to the release branch for LLVM 7.1

[tstellar]

Merged: r344917

[tstellar]

mentioned in issue #38454