Build fails with strict-aliasing violations

[eli-schwartz]

I tried to compile with LTO: -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing

The -Werror=* flags are important to detect cases where the compiler can try to optimize based on assuming UB cannot happen, and miscompile code that has UB in it. strict-aliasing issues are always bad but LTO can make them even worse.

I got this error:

[8/18] /usr/bin/x86_64-pc-linux-gnu-g++ -DPACKAGE=\"CTL\" -DVERSION=\"1.5.3\" -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/dpx -isystem /usr/include/Imath  -march=native -fstack-protector-all -O2 -pipe -fdiagnostics-color=always -frecord-gcc-switches -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing  -Wformat -Werror=format-security -std=gnu++11 -MD -MT lib/dpx/CMakeFiles/ctldpx.dir/dpx_raw.cc.o -MF lib/dpx/CMakeFiles/ctldpx.dir/dpx_raw.cc.o.d -o lib/dpx/CMakeFiles/ctldpx.dir/dpx_raw.cc.o -c /var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/dpx/dpx_raw.cc
FAILED: lib/dpx/CMakeFiles/ctldpx.dir/dpx_raw.cc.o 
/usr/bin/x86_64-pc-linux-gnu-g++ -DPACKAGE=\"CTL\" -DVERSION=\"1.5.3\" -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/dpx -isystem /usr/include/Imath  -march=native -fstack-protector-all -O2 -pipe -fdiagnostics-color=always -frecord-gcc-switches -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing  -Wformat -Werror=format-security -std=gnu++11 -MD -MT lib/dpx/CMakeFiles/ctldpx.dir/dpx_raw.cc.o -MF lib/dpx/CMakeFiles/ctldpx.dir/dpx_raw.cc.o.d -o lib/dpx/CMakeFiles/ctldpx.dir/dpx_raw.cc.o -c /var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/dpx/dpx_raw.cc
/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/dpx/dpx_raw.cc: In static member function ‘static bool ctl::dpx::isnull(float32_t)’:
/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/dpx/dpx_raw.cc:209:18: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
  209 |         return *((uint32_t *)&v)==(uint32_t)-1;
      |                 ~^~~~~~~~~~~~~~~
cc1plus: some warnings being treated as errors
[9/18] /usr/bin/x86_64-pc-linux-gnu-g++ -DIlmCtlSimd_EXPORTS -DPACKAGE=\"CTL\" -DVERSION=\"1.5.3\" -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3_build/lib/IlmCtlSimd -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlMath -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtl -isystem /usr/include/OpenEXR -isystem /usr/include/Imath  -march=native -fstack-protector-all -O2 -pipe -fdiagnostics-color=always -frecord-gcc-switches -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing  -Wformat -Werror=format-security -std=gnu++11 -fPIC -MD -MT lib/IlmCtlSimd/CMakeFiles/IlmCtlSimd.dir/CtlSimdStdLibMath.cpp.o -MF lib/IlmCtlSimd/CMakeFiles/IlmCtlSimd.dir/CtlSimdStdLibMath.cpp.o.d -o lib/IlmCtlSimd/CMakeFiles/IlmCtlSimd.dir/CtlSimdStdLibMath.cpp.o -c /var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd/CtlSimdStdLibMath.cpp
FAILED: lib/IlmCtlSimd/CMakeFiles/IlmCtlSimd.dir/CtlSimdStdLibMath.cpp.o 
/usr/bin/x86_64-pc-linux-gnu-g++ -DIlmCtlSimd_EXPORTS -DPACKAGE=\"CTL\" -DVERSION=\"1.5.3\" -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3_build/lib/IlmCtlSimd -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlMath -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtl -isystem /usr/include/OpenEXR -isystem /usr/include/Imath  -march=native -fstack-protector-all -O2 -pipe -fdiagnostics-color=always -frecord-gcc-switches -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing  -Wformat -Werror=format-security -std=gnu++11 -fPIC -MD -MT lib/IlmCtlSimd/CMakeFiles/IlmCtlSimd.dir/CtlSimdStdLibMath.cpp.o -MF lib/IlmCtlSimd/CMakeFiles/IlmCtlSimd.dir/CtlSimdStdLibMath.cpp.o.d -o lib/IlmCtlSimd/CMakeFiles/IlmCtlSimd.dir/CtlSimdStdLibMath.cpp.o -c /var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd/CtlSimdStdLibMath.cpp
In file included from /var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd/CtlSimdHalfExpLog.h:70,
                 from /var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd/CtlSimdStdLibMath.cpp:69:
/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd/halfExpLog.h: In function ‘float Ctl::log10_h(half)’:
/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd/halfExpLog.h:15:13: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
   15 |     return *(float *)(&log10Table[x.bits()]);
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd/halfExpLog.h: In function ‘float Ctl::log_h(half)’:
/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd/halfExpLog.h:22:13: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
   22 |     return *(float *)(&logTable[x.bits()]);
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1plus: some warnings being treated as errors
[10/18] /usr/bin/x86_64-pc-linux-gnu-g++ -DIlmCtlSimd_EXPORTS -DPACKAGE=\"CTL\" -DVERSION=\"1.5.3\" -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3_build/lib/IlmCtlSimd -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlMath -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtl -isystem /usr/include/OpenEXR -isystem /usr/include/Imath  -march=native -fstack-protector-all -O2 -pipe -fdiagnostics-color=always -frecord-gcc-switches -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing  -Wformat -Werror=format-security -std=gnu++11 -fPIC -MD -MT lib/IlmCtlSimd/CMakeFiles/IlmCtlSimd.dir/CtlSimdHalfExpLog.cpp.o -MF lib/IlmCtlSimd/CMakeFiles/IlmCtlSimd.dir/CtlSimdHalfExpLog.cpp.o.d -o lib/IlmCtlSimd/CMakeFiles/IlmCtlSimd.dir/CtlSimdHalfExpLog.cpp.o -c /var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd/CtlSimdHalfExpLog.cpp
FAILED: lib/IlmCtlSimd/CMakeFiles/IlmCtlSimd.dir/CtlSimdHalfExpLog.cpp.o 
/usr/bin/x86_64-pc-linux-gnu-g++ -DIlmCtlSimd_EXPORTS -DPACKAGE=\"CTL\" -DVERSION=\"1.5.3\" -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3_build/lib/IlmCtlSimd -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlMath -I/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtl -isystem /usr/include/OpenEXR -isystem /usr/include/Imath  -march=native -fstack-protector-all -O2 -pipe -fdiagnostics-color=always -frecord-gcc-switches -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing  -Wformat -Werror=format-security -std=gnu++11 -fPIC -MD -MT lib/IlmCtlSimd/CMakeFiles/IlmCtlSimd.dir/CtlSimdHalfExpLog.cpp.o -MF lib/IlmCtlSimd/CMakeFiles/IlmCtlSimd.dir/CtlSimdHalfExpLog.cpp.o.d -o lib/IlmCtlSimd/CMakeFiles/IlmCtlSimd.dir/CtlSimdHalfExpLog.cpp.o -c /var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd/CtlSimdHalfExpLog.cpp
In file included from /var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd/CtlSimdHalfExpLog.h:70,
                 from /var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd/CtlSimdHalfExpLog.cpp:63:
/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd/halfExpLog.h: In function ‘float Ctl::log10_h(half)’:
/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd/halfExpLog.h:15:13: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
   15 |     return *(float *)(&log10Table[x.bits()]);
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd/halfExpLog.h: In function ‘float Ctl::log_h(half)’:
/var/tmp/portage/media-libs/ctl-1.5.3/work/CTL-ctl-1.5.3/lib/IlmCtlSimd/halfExpLog.h:22:13: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
   22 |     return *(float *)(&logTable[x.bits()]);
      |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1plus: some warnings being treated as errors
ninja: build stopped: subcommand failed.

Downtream report: https://bugs.gentoo.org/926823
Full build log: build.log

[michaeldsmith]

@eli-schwartz thank you for reporting this issue. I think I have addressed the issue you have reported with PR #147. Please let us know if that PR resolves the issue for you or if you have any other suggestions or input, etc.

[eli-schwartz]

Thanks. I tried applying the patches from that PR onto the 1.5.3 release and everything compiled fine.

No more commments in particular (though I guess I am a bit surprised that vcpkg hasn't gone and pinned to say an archive.org copy of the tarball for the version they reverted to).

[michaeldsmith]

thanks - i agree that the vcpkg thing is a surprise. I think the XV backdoor issue will probably take some time to resolve since the bad actor may have been contributing for a while. Wired has a long piece on it here https://www.wired.com/story/xz-backdoor-everything-you-need-to-know/

[eli-schwartz]

FWIW it may not be as bad as all that. The bad actor has been contributing since 2021 but it's only since the beginning of 2024 or thereabouts that the original author's guard was lowered enough to put these pieces into place. Status updates will be at https://tukaani.org/xz-backdoor/ and indicate we may not have to wait too long...

[michaeldsmith]

closed by 7133fc2