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:
[1/7] /usr/bin/x86_64-pc-linux-gnu-gcc -DARRAY_IMPORTS -DCCSYSYEM_IMPORTS -DCHARCONVERT_IMPORTS -DDATE_IMPORTS -DEBML2_UGLY_HACKS_API -DFILE_IMPORTS -DHAS_EBML2 -DMD5_IMPORTS -DMULTITHREAD_IMPORTS -DNODE_IMPORTS -DSTR_IMPORTS -Debml2_EXPORTS -Debml2_IMPORTS -I/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0_build/libebml2 -I/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/libebml2 -I/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec -I/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/helpers -I/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/.. -I/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0_build/corec/corec -pipe -march=native -fstack-protector-all -O2 -fdiagnostics-color=always -frecord-gcc-switches -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing -Wformat -Werror=format-security -Werror=implicit-function-declaration -Werror=implicit-int -Werror=int-conversion -Werror=incompatible-pointer-types -Wno-error=format-security -fPIC -MD -MT libebml2/CMakeFiles/ebml2.dir/ebmlnumber.c.o -MF libebml2/CMakeFiles/ebml2.dir/ebmlnumber.c.o.d -o libebml2/CMakeFiles/ebml2.dir/ebmlnumber.c.o -c /var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/libebml2/ebmlnumber.c
FAILED: libebml2/CMakeFiles/ebml2.dir/ebmlnumber.c.o
/usr/bin/x86_64-pc-linux-gnu-gcc -DARRAY_IMPORTS -DCCSYSYEM_IMPORTS -DCHARCONVERT_IMPORTS -DDATE_IMPORTS -DEBML2_UGLY_HACKS_API -DFILE_IMPORTS -DHAS_EBML2 -DMD5_IMPORTS -DMULTITHREAD_IMPORTS -DNODE_IMPORTS -DSTR_IMPORTS -Debml2_EXPORTS -Debml2_IMPORTS -I/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0_build/libebml2 -I/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/libebml2 -I/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec -I/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/helpers -I/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/.. -I/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0_build/corec/corec -pipe -march=native -fstack-protector-all -O2 -fdiagnostics-color=always -frecord-gcc-switches -flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing -Wformat -Werror=format-security -Werror=implicit-function-declaration -Werror=implicit-int -Werror=int-conversion -Werror=incompatible-pointer-types -Wno-error=format-security -fPIC -MD -MT libebml2/CMakeFiles/ebml2.dir/ebmlnumber.c.o -MF libebml2/CMakeFiles/ebml2.dir/ebmlnumber.c.o.d -o libebml2/CMakeFiles/ebml2.dir/ebmlnumber.c.o -c /var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/libebml2/ebmlnumber.c
In file included from /var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/corec.h:46,
from /var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/node/node.h:33,
from /var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/libebml2/ebml2/ebml.h:32,
from /var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/libebml2/ebmlnumber.c:28:
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/libebml2/ebmlnumber.c: In function ‘RenderDataFloat’:
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:89:42: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
89 | #define LOAD64BE(ptr) INT64BE(*(uint64_t*)(ptr))
| ^~~~~~~~~~~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:54:33: note: in definition of macro ‘SWAP32’
54 | #define SWAP32(a) ((((uint32_t)(a) >> 24) & 0x000000FF) | (((uint32_t)(a) >> 8) & 0x0000FF00)|\
| ^
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:75:20: note: in expansion of macro ‘SWAP64’
75 | #define INT64BE(a) SWAP64(a)
| ^~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:89:33: note: in expansion of macro ‘INT64BE’
89 | #define LOAD64BE(ptr) INT64BE(*(uint64_t*)(ptr))
| ^~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/libebml2/ebmlnumber.c:187:15: note: in expansion of macro ‘LOAD64BE’
187 | Buf = LOAD64BE(&data.i);
| ^~~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:89:42: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
89 | #define LOAD64BE(ptr) INT64BE(*(uint64_t*)(ptr))
| ^~~~~~~~~~~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:54:72: note: in definition of macro ‘SWAP32’
54 | #define SWAP32(a) ((((uint32_t)(a) >> 24) & 0x000000FF) | (((uint32_t)(a) >> 8) & 0x0000FF00)|\
| ^
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:75:20: note: in expansion of macro ‘SWAP64’
75 | #define INT64BE(a) SWAP64(a)
| ^~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:89:33: note: in expansion of macro ‘INT64BE’
89 | #define LOAD64BE(ptr) INT64BE(*(uint64_t*)(ptr))
| ^~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/libebml2/ebmlnumber.c:187:15: note: in expansion of macro ‘LOAD64BE’
187 | Buf = LOAD64BE(&data.i);
| ^~~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:89:42: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
89 | #define LOAD64BE(ptr) INT64BE(*(uint64_t*)(ptr))
| ^~~~~~~~~~~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:55:32: note: in definition of macro ‘SWAP32’
55 | (((uint32_t)(a) << 8) & 0x00FF0000) | (((uint32_t)(a) << 24) & 0xFF000000))
| ^
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:75:20: note: in expansion of macro ‘SWAP64’
75 | #define INT64BE(a) SWAP64(a)
| ^~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:89:33: note: in expansion of macro ‘INT64BE’
89 | #define LOAD64BE(ptr) INT64BE(*(uint64_t*)(ptr))
| ^~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/libebml2/ebmlnumber.c:187:15: note: in expansion of macro ‘LOAD64BE’
187 | Buf = LOAD64BE(&data.i);
| ^~~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:89:42: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
89 | #define LOAD64BE(ptr) INT64BE(*(uint64_t*)(ptr))
| ^~~~~~~~~~~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:55:71: note: in definition of macro ‘SWAP32’
55 | (((uint32_t)(a) << 8) & 0x00FF0000) | (((uint32_t)(a) << 24) & 0xFF000000))
| ^
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:75:20: note: in expansion of macro ‘SWAP64’
75 | #define INT64BE(a) SWAP64(a)
| ^~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:89:33: note: in expansion of macro ‘INT64BE’
89 | #define LOAD64BE(ptr) INT64BE(*(uint64_t*)(ptr))
| ^~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/libebml2/ebmlnumber.c:187:15: note: in expansion of macro ‘LOAD64BE’
187 | Buf = LOAD64BE(&data.i);
| ^~~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:89:42: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
89 | #define LOAD64BE(ptr) INT64BE(*(uint64_t*)(ptr))
| ^~~~~~~~~~~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:54:33: note: in definition of macro ‘SWAP32’
54 | #define SWAP32(a) ((((uint32_t)(a) >> 24) & 0x000000FF) | (((uint32_t)(a) >> 8) & 0x0000FF00)|\
| ^
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:75:20: note: in expansion of macro ‘SWAP64’
75 | #define INT64BE(a) SWAP64(a)
| ^~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:89:33: note: in expansion of macro ‘INT64BE’
89 | #define LOAD64BE(ptr) INT64BE(*(uint64_t*)(ptr))
| ^~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/libebml2/ebmlnumber.c:187:15: note: in expansion of macro ‘LOAD64BE’
187 | Buf = LOAD64BE(&data.i);
| ^~~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:89:42: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
89 | #define LOAD64BE(ptr) INT64BE(*(uint64_t*)(ptr))
| ^~~~~~~~~~~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:54:72: note: in definition of macro ‘SWAP32’
54 | #define SWAP32(a) ((((uint32_t)(a) >> 24) & 0x000000FF) | (((uint32_t)(a) >> 8) & 0x0000FF00)|\
| ^
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:75:20: note: in expansion of macro ‘SWAP64’
75 | #define INT64BE(a) SWAP64(a)
| ^~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:89:33: note: in expansion of macro ‘INT64BE’
89 | #define LOAD64BE(ptr) INT64BE(*(uint64_t*)(ptr))
| ^~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/libebml2/ebmlnumber.c:187:15: note: in expansion of macro ‘LOAD64BE’
187 | Buf = LOAD64BE(&data.i);
| ^~~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:89:42: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
89 | #define LOAD64BE(ptr) INT64BE(*(uint64_t*)(ptr))
| ^~~~~~~~~~~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:55:32: note: in definition of macro ‘SWAP32’
55 | (((uint32_t)(a) << 8) & 0x00FF0000) | (((uint32_t)(a) << 24) & 0xFF000000))
| ^
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:75:20: note: in expansion of macro ‘SWAP64’
75 | #define INT64BE(a) SWAP64(a)
| ^~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:89:33: note: in expansion of macro ‘INT64BE’
89 | #define LOAD64BE(ptr) INT64BE(*(uint64_t*)(ptr))
| ^~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/libebml2/ebmlnumber.c:187:15: note: in expansion of macro ‘LOAD64BE’
187 | Buf = LOAD64BE(&data.i);
| ^~~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:89:42: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
89 | #define LOAD64BE(ptr) INT64BE(*(uint64_t*)(ptr))
| ^~~~~~~~~~~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:55:71: note: in definition of macro ‘SWAP32’
55 | (((uint32_t)(a) << 8) & 0x00FF0000) | (((uint32_t)(a) << 24) & 0xFF000000))
| ^
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:75:20: note: in expansion of macro ‘SWAP64’
75 | #define INT64BE(a) SWAP64(a)
| ^~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/corec/corec/../corec/helper.h:89:33: note: in expansion of macro ‘INT64BE’
89 | #define LOAD64BE(ptr) INT64BE(*(uint64_t*)(ptr))
| ^~~~~~~
/var/tmp/portage/media-video/mkclean-0.9.0/work/mkclean-0.9.0/libebml2/ebmlnumber.c:187:15: note: in expansion of macro ‘LOAD64BE’
187 | Buf = LOAD64BE(&data.i);
| ^~~~~~~~
cc1: some warnings being treated as errors
ninja: build stopped: cannot make progress due to previous errors.
* ERROR: media-video/mkclean-0.9.0::gentoo failed (compile phase):
I tried to build with the following *FLAGS to optimize the build:
-flto=4 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasingThe -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:
Originally reported downstream: https://bugs.gentoo.org/861134 Full build log: build.log
Reproduced with 0.8.10, 0.9.0, and git master.