Re: [PATCH] timespec: fill in other members

[Pádraig Brady]

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.  */
      |                     ^~~~~~~