LLVM12+UBSan: undefined symbol: _stpcpy

[MasterNobody]

Trying to compile x264 with UndefinedBehaviorSanitizer
./configure --extra-cflags="-fsanitize=undefined" --extra-ldflags="-fsanitize=undefined"
fails with linker error:

lld-link: error: undefined symbol: _stpcpy
>>> referenced by x264.o:(_stringify_names)
clang-12: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [Makefile:264: x264.exe] Error 1

Adding -fno-builtin-stpcpy to CFLAGS helps but this looks like regression of LLVM12. But I don't understand why it fails only when using sanitizers.

[mstorsjo]

I bisected the breakage down to this commit: llvm/llvm-project@6dbf0cf

commit 6dbf0cfcf789365493f70ae69df8a7a59be41c75
Author: Dávid Bolvanský <david.bolvansky@gmail.com>
Date:   Fri Aug 14 23:48:30 2020 +0200

    [SLC] sprintf(dst, "%s", str) -> strcpy(dst, str)
    
    Transform sprintf(dst, "%s", str) -> strcpy(dst, str) if result is unused
    Avoid sprintf(dest, "%s", str) -> llvm.memcpy(align 1 dest, align 1 str, strlen(str)+1) if optimizing for size.
    
    Reviewed By: efriedma
    
    Differential Revision: https://reviews.llvm.org/D85963

I guess the optimization is evaluated differently (not doable or not worth it) if sanitizers aren't used...

I'll have a look later at if we can mark stpcpy or this optimization as unavailable for mingw targets.

[mstorsjo]

A patch fixing this issue is posted at https://reviews.llvm.org/D102946 now.

[mstorsjo]

Fixed upstream in llvm/llvm-project@c5638a7.

[mstorsjo]

Reopening the bug until there's a new release of llvm-mingw with the fix.

[RussellHaley]

Ha. Just landed on this using the python branch, thanks for leaving it open!

error: lld-link: error: undefined symbol: _stpcpy
>>> referenced by build/.objs/lua54-lib/mingw/i686/release/__/__/sources/work/lua-5.4.3/src/lstrlib.c.obj:(_str_format)
clang: error: linker command failed with exit code 1 (use -v to see invocation)

russellh@jailbird /s/s/XMakeWinLua (master)> x86_64-w64-mingw32-clang --version
clang version 12.0.0 (https://github.com/llvm/llvm-project.git fc887d1c2b8c359279b01856f6f1fd70c69f132b)
Target: x86_64-w64-windows-gnu
Thread model: posix
InstalledDir: /storage/build/llvm-mingw-host/bin

[mstorsjo]

I made a new release today, with LLVM 13.0.0 RC1, which contains the fix for this issue.