On 15/05/2023 07:30, Paul Eggert wrote:
This problem was found when compiling GNU Emacs with --enable-gcc-warnings on a platform where tv_sec is 64 bits and tv_nsec is 32 bits, and struct timespec has padding. GCC -Wuse-of-uninitialized-value complained when a struct timespec initialized only via assigning to tv_sec and tv_nsec was copied via assignment (this was in lib/timespec.h’s make_timespec). Although behavior is well-defined on this platform, the warning is annoying and the behavior might not be well-defined on theoretical platforms where struct timespec has other members. To work around this, initialize all the struct’s members.
* lib/utimecmp.c (utimecmpat): * lib/utimens.c (fdutimens): When filling in a struct timespec or similar time-related structure that might be copied elsewhere, also assign to any storage other than tv_sec and tv_nsec, to avoid undefined behavior on (likely theoretical) platforms where struct timespec has other members, and also to avoid warnings from GCC and/or valgrind.
The new coreutils CI I have in place is failing to build with gcc (Debian 10.2.1-6) 10.2.1 with gnulib latest (ebd843b3) as follows. I think this may be due to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82283 It's a pity that doesn't seem to have been backported to gcc 10 (2020). I was thinking I might need to ./configure --enable-gcc-warnings=no for CI at some stage, but it seems that's sooner rather than later. It might be worth reverting the change to lib/utimecmp.c and perhaps instead initializing with `= {0}`. I confirmed that builds without issue. cheers, Pádraig lib/utimecmp.c: In function 'utimecmpat': lib/utimecmp.c:348:17: error: missing initializer for field 'tv_nsec' of 'struct timespec' [-Werror=missing-field-initializers] 348 | [0].tv_nsec = dst_a_ns, | ^ In file included from /usr/include/x86_64-linux-gnu/sys/select.h:39, from ./lib/sys/select.h:114, from /usr/include/x86_64-linux-gnu/sys/types.h:179, from ./lib/sys/types.h:46, from lib/utimecmp.h:23, from lib/utimecmp.c:22: /usr/include/x86_64-linux-gnu/bits/types/struct_timespec.h:16:21: note: 'tv_nsec' declared here 16 | __syscall_slong_t tv_nsec; /* Nanoseconds. */ | ^~~~~~~ lib/utimecmp.c:350:17: error: missing initializer for field 'tv_nsec' of 'struct timespec' [-Werror=missing-field-initializers] 350 | [1].tv_nsec = dst_m_ns + res / 9 | ^ In file included from /usr/include/x86_64-linux-gnu/sys/select.h:39, from ./lib/sys/select.h:114, from /usr/include/x86_64-linux-gnu/sys/types.h:179, from ./lib/sys/types.h:46, from lib/utimecmp.h:23, from lib/utimecmp.c:22: /usr/include/x86_64-linux-gnu/bits/types/struct_timespec.h:16:21: note: 'tv_nsec' declared here 16 | __syscall_slong_t tv_nsec; /* Nanoseconds. */ | ^~~~~~~
