Build fails with strict-aliasing violations

[eli-schwartz]

I tried to build with the following *FLAGS to optimize the build: -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:

[1/625] /usr/lib/ccache/bin/x86_64-pc-linux-gnu-g++ -DHAVE_CONFIG_H -DLAF_LINUX -DLAF_SKIA -DNDEBUG -DPNG_NO_MMX_CODE -I/usr/include/pixman-1 -I/usr/include/freetype2 -I/usr/include/harfbuzz -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/third_party/simpleini -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/aseprite-1.3.6_build/laf -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/src -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=c++17 -MD -MT laf/base/CMakeFiles/laf-base.dir/cfile.cpp.o -MF laf/base/CMakeFiles/laf-base.dir/cfile.cpp.o.d -o laf/base/CMakeFiles/laf-base.dir/cfile.cpp.o -c /var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/cfile.cpp
FAILED: laf/base/CMakeFiles/laf-base.dir/cfile.cpp.o 
/usr/lib/ccache/bin/x86_64-pc-linux-gnu-g++ -DHAVE_CONFIG_H -DLAF_LINUX -DLAF_SKIA -DNDEBUG -DPNG_NO_MMX_CODE -I/usr/include/pixman-1 -I/usr/include/freetype2 -I/usr/include/harfbuzz -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/third_party/simpleini -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/aseprite-1.3.6_build/laf -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/src -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=c++17 -MD -MT laf/base/CMakeFiles/laf-base.dir/cfile.cpp.o -MF laf/base/CMakeFiles/laf-base.dir/cfile.cpp.o.d -o laf/base/CMakeFiles/laf-base.dir/cfile.cpp.o -c /var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/cfile.cpp
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/cfile.cpp: In function ‘float base::fgetf(FILE*)’:
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/cfile.cpp:117:11: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
  117 |   return *reinterpret_cast<float*>(&v);
      |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/cfile.cpp: In function ‘double base::fgetd(FILE*)’:
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/cfile.cpp:159:11: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
  159 |   return *reinterpret_cast<double*>(&v);
      |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/cfile.cpp: In function ‘int base::fputf(float, FILE*)’:
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/cfile.cpp:234:19: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
  234 |   const int b = *(reinterpret_cast<int*>(&l));
      |                  ~^~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/cfile.cpp: In function ‘int base::fputd(double, FILE*)’:
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/cfile.cpp:257:25: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
  257 |   const long long b = *(reinterpret_cast<long long*>(&l));
      |                        ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1plus: some warnings being treated as errors
[2/625] /usr/lib/ccache/bin/x86_64-pc-linux-gnu-g++ -DHAVE_CONFIG_H -DLAF_LINUX -DLAF_SKIA -DNDEBUG -DPNG_NO_MMX_CODE -I/usr/include/pixman-1 -I/usr/include/freetype2 -I/usr/include/harfbuzz -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/third_party/simpleini -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/aseprite-1.3.6_build/laf -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/src -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=c++17 -MD -MT laf/base/CMakeFiles/laf-base.dir/serialization.cpp.o -MF laf/base/CMakeFiles/laf-base.dir/serialization.cpp.o.d -o laf/base/CMakeFiles/laf-base.dir/serialization.cpp.o -c /var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp
FAILED: laf/base/CMakeFiles/laf-base.dir/serialization.cpp.o 
/usr/lib/ccache/bin/x86_64-pc-linux-gnu-g++ -DHAVE_CONFIG_H -DLAF_LINUX -DLAF_SKIA -DNDEBUG -DPNG_NO_MMX_CODE -I/usr/include/pixman-1 -I/usr/include/freetype2 -I/usr/include/harfbuzz -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/third_party/simpleini -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/aseprite-1.3.6_build/laf -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/src -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=c++17 -MD -MT laf/base/CMakeFiles/laf-base.dir/serialization.cpp.o -MF laf/base/CMakeFiles/laf-base.dir/serialization.cpp.o.d -o laf/base/CMakeFiles/laf-base.dir/serialization.cpp.o -c /var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp: In function ‘std::ostream& base::serialization::little_endian::write_float(std::ostream&, float)’:
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp:60:19: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
   60 |   const int b = *(reinterpret_cast<int*>(&value));
      |                  ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp: In function ‘std::ostream& base::serialization::little_endian::write_double(std::ostream&, double)’:
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp:70:25: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
   70 |   const long long b = *(reinterpret_cast<long long*>(&value));
      |                        ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp: In function ‘float base::serialization::little_endian::read_float(std::istream&)’:
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp:129:11: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
  129 |   return *reinterpret_cast<float*>(&v);
      |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp: In function ‘double base::serialization::little_endian::read_double(std::istream&)’:
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp:151:11: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
  151 |   return *reinterpret_cast<double*>(&v);
      |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp: In function ‘std::ostream& base::serialization::big_endian::write_float(std::ostream&, float)’:
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp:185:19: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
  185 |   const int b = *(reinterpret_cast<int*>(&value));
      |                  ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp: In function ‘std::ostream& base::serialization::big_endian::write_double(std::ostream&, double)’:
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp:195:25: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
  195 |   const long long b = *(reinterpret_cast<long long*>(&value));
      |                        ~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp: In function ‘float base::serialization::big_endian::read_float(std::istream&)’:
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp:254:11: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
  254 |   return *reinterpret_cast<float*>(&v);
      |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp: In function ‘double base::serialization::big_endian::read_double(std::istream&)’:
/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf/base/serialization.cpp:276:11: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
  276 |   return *reinterpret_cast<double*>(&v);
      |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1plus: some warnings being treated as errors
[3/625] /usr/lib/ccache/bin/x86_64-pc-linux-gnu-g++ -DENABLE_DATA_RECOVERY -DENABLE_NEWS -DENABLE_SAVE -DENABLE_SCRIPTING -DENABLE_UI -DENABLE_WEBSOCKET -DHAVE_CONFIG_H -DHAVE_CONFIG_OVERRIDE_H=1 -DLAF_LINUX -DLAF_SKIA -DLAF_WITH_REGION -DNDEBUG -DPNG_NO_MMX_CODE -DSK_ALLOW_STATIC_GLOBAL_INITIALIZERS=1 -DSK_BUILD_FOR_UNIX -DSK_ENABLE_SKSL=1 -DSK_GAMMA_APPLY_TO_A8 -DSK_GAMMA_SRGB -DSK_GL=1 -DSK_INTERNAL -DSK_R32_SHIFT=16 -DSK_SCALAR_TO_FLOAT_EXCLUDED -DSK_SUPPORT_GPU=1 -I/usr/include/pixman-1 -I/usr/include/freetype2 -I/usr/include/harfbuzz -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/third_party/simpleini -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/src/observable -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/src/dio/.. -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/aseprite-1.3.6_build/laf -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/src -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/src/fixmath/.. -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/src/doc/.. -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/skia-3338e90707323d2cd3a150276acb9f39933deee2 -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/third_party/cityhash/src -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 -Wall -Wno-switch -Wimplicit-fallthrough -std=c++17   -Wno-sign-compare -MD -MT src/dio/CMakeFiles/dio-lib.dir/aseprite_decoder.cpp.o -MF src/dio/CMakeFiles/dio-lib.dir/aseprite_decoder.cpp.o.d -o src/dio/CMakeFiles/dio-lib.dir/aseprite_decoder.cpp.o -c /var/tmp/portage/dev-games/aseprite-1.3.6/work/src/dio/aseprite_decoder.cpp
FAILED: src/dio/CMakeFiles/dio-lib.dir/aseprite_decoder.cpp.o 
/usr/lib/ccache/bin/x86_64-pc-linux-gnu-g++ -DENABLE_DATA_RECOVERY -DENABLE_NEWS -DENABLE_SAVE -DENABLE_SCRIPTING -DENABLE_UI -DENABLE_WEBSOCKET -DHAVE_CONFIG_H -DHAVE_CONFIG_OVERRIDE_H=1 -DLAF_LINUX -DLAF_SKIA -DLAF_WITH_REGION -DNDEBUG -DPNG_NO_MMX_CODE -DSK_ALLOW_STATIC_GLOBAL_INITIALIZERS=1 -DSK_BUILD_FOR_UNIX -DSK_ENABLE_SKSL=1 -DSK_GAMMA_APPLY_TO_A8 -DSK_GAMMA_SRGB -DSK_GL=1 -DSK_INTERNAL -DSK_R32_SHIFT=16 -DSK_SCALAR_TO_FLOAT_EXCLUDED -DSK_SUPPORT_GPU=1 -I/usr/include/pixman-1 -I/usr/include/freetype2 -I/usr/include/harfbuzz -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/third_party/simpleini -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/src/observable -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/src/dio/.. -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/laf -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/aseprite-1.3.6_build/laf -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/src -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/src/fixmath/.. -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/src/doc/.. -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/skia-3338e90707323d2cd3a150276acb9f39933deee2 -I/var/tmp/portage/dev-games/aseprite-1.3.6/work/third_party/cityhash/src -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 -Wall -Wno-switch -Wimplicit-fallthrough -std=c++17   -Wno-sign-compare -MD -MT src/dio/CMakeFiles/dio-lib.dir/aseprite_decoder.cpp.o -MF src/dio/CMakeFiles/dio-lib.dir/aseprite_decoder.cpp.o.d -o src/dio/CMakeFiles/dio-lib.dir/aseprite_decoder.cpp.o -c /var/tmp/portage/dev-games/aseprite-1.3.6/work/src/dio/aseprite_decoder.cpp
/var/tmp/portage/dev-games/aseprite-1.3.6/work/src/dio/aseprite_decoder.cpp: In member function ‘float dio::AsepriteDecoder::readFloat()’:
/var/tmp/portage/dev-games/aseprite-1.3.6/work/src/dio/aseprite_decoder.cpp:428:11: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
  428 |   return *reinterpret_cast<float*>(&v);
      |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/var/tmp/portage/dev-games/aseprite-1.3.6/work/src/dio/aseprite_decoder.cpp: In member function ‘double dio::AsepriteDecoder::readDouble()’:
/var/tmp/portage/dev-games/aseprite-1.3.6/work/src/dio/aseprite_decoder.cpp:468:11: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
  468 |   return *reinterpret_cast<double*>(&v);
      |           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1plus: some warnings being treated as errors
ninja: build stopped: cannot make progress due to previous errors.

Originally reported downstream: https://bugs.gentoo.org/924692
Full build log: build.log

[winterheart]

Recent laf main code don't has reinterpret_cast invocations, so these errors may be fixed by fetching recent laf codebase.

[eli-schwartz]

My report is about 1.3.6

v1.3.6...main

Which part of the commits since 1.3.6 do you believe solved this issue?

[winterheart]

Sorry, misread source code. Proposed PR aseprite/laf#84 intended to fix this.