Bug#973495: mingw-w64-common: Conflicting definition of std::max_align_t with stddef.h of gcc-mingw-w64-i686-posix
Control: forwarded -1 https://sourceforge.net/p/mingw-w64/bugs/778/ On Sat, 31 Oct 2020 21:10:50 +, Jonathan Wakely wrote: > This is https://sourceforge.net/p/mingw-w64/bugs/778/ and is being discussed on the mailing list: https://sourceforge.net/p/mingw-w64/mailman/mingw-w64-public/thread/19d95ae7-cd88-c558-5990-b4e34b75ea69%40users.sourceforge.net/#msg37141563 Regards, Stephen pgpapQKWHLhyq.pgp Description: OpenPGP digital signature
Bug#973495: mingw-w64-common: Conflicting definition of std::max_align_t with stddef.h of gcc-mingw-w64-i686-posix
This is https://sourceforge.net/p/mingw-w64/bugs/778/
Bug#973495: mingw-w64-common: Conflicting definition of std::max_align_t with stddef.h of gcc-mingw-w64-i686-posix
A minimal reproducer: #ifdef STDDEF_FIRST # include #endif #include static_assert( alignof(max_align_t) == 16 ); $ x86_64-w64-mingw32-g++ -c max.cc -m32 && echo ok ok $ x86_64-w64-mingw32-g++ -c max.cc -m32 -DSTDDEF_FIRST && echo ok max.cc:6:37: error: static assertion failed 6 | static_assert( alignof(max_align_t) == 16 ); |~^ The problem is that includes after defining __need_wint_t and __need_wchar_t. GCC's is included, which immediately does #include_next , which finds the base mingw , which does almost nothing because __need_wint_t and __need_wchar_t are defined: # 29 "/usr/share/mingw-w64/include/stdint.h" 2 3 4 #define __need_wint_t #define __need_wchar_t #include # 32 "/usr/share/mingw-w64/include/stdint.h" 3 4 # 1 "/usr/lib/gcc/i686-w64-mingw32/10-posix/include/stddef.h" 1 3 4 #include_next # 1 "/usr/lib/gcc/i686-w64-mingw32/10-posix/include/stddef.h" 3 4 # 1 "/usr/share/mingw-w64/include/stddef.h" 1 3 4 After defining wchar_t and wint_t the mingw does almost nothing else, skipping the rest of that header. We then return to GCC's , which sees that max_align_t has not been defined yet, and so defines it (using the modern definition that includes __float128). When STDDEF_FIRST is defined in the reproducer above, is included without defining __need_wint_t and __need_wchar_t, which means the base mingw defines everything, not just those two types. That includes the old definition of max_align_t, without __float128. GCC's sees that _GCC_MAX_ALIGN_T has been defined, so doesn't both to define it again. So whether you get the old max_align_t from mingw's or the new max_align_t from GCC's depends on whether gets included directly or as a side effect of including some other header. The simplest solution would be to just add the __float128 member to max_align_t in the mingw header.
Bug#973495: mingw-w64-common: Conflicting definition of std::max_align_t with stddef.h of gcc-mingw-w64-i686-posix
Package: mingw-w64-common Version: 8.0.0-1 Severity: important Dear Maintainer, When cross compiling for 32-bit Windows, I noticed that some translation units had a different value for std::max_align_t than others. It appears that (for some reason), one included it from: /usr/share/mingw-w64/include/stddef.h and another from: /usr/lib/gcc/i686-w64-mingw32/10-posix/include/stddef.h These have conflicting definitions, see http://paste.debian.net/1169371/ According to people on #gcc IRC: the issue seems to be that one of your stddef headers is old and predates the addition of __float128 support, which required increasing the alignment of max_align_t If this is true, then something is wrong with the stddef.h in mingw-w64-common, as it doesn't include that __float128 support. (But I wonder in the first place why both mingw-w64-common and gcc-mingw-w64-i686-posix provide a stddef.h, which apparently both can be found and then have a different definition...!?) Anyway, this is all not my specialism, but I think it's still important to report it. Please let me know if you need more information. I'll do my best to provide it. Thanks for taking a look at this! Kind regards, Manuel -- System Information: Debian Release: bullseye/sid APT prefers testing APT policy: (500, 'testing'), (1, 'experimental') Architecture: amd64 (x86_64) Foreign Architectures: i386 Kernel: Linux 5.8.0-3-amd64 (SMP w/4 CPU threads) Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE=en_US:en Shell: /bin/sh linked to /bin/dash Init: systemd (via /run/systemd/system) LSM: AppArmor: enabled -- no debconf information
