Refactor tr2_dst_try_uds_connect() to avoid a gcc warning[1] that
appears under -O3 (but not -O2). This makes the build pass under
DEVELOPER=1 without needing a DEVOPTS=no-error.
This can be reproduced with GCC Debian 8.3.0-6, but not e.g. with
clang 7.0.1-8+deb10u2. We've had this warning since
ee4512ed48 (trace2: create new combined trace facility, 2019-02-22).
As noted in [2] this warning happens because the compiler doesn't
assume that errno must be non-zero after a failed syscall.
Let's work around by using the well-established "saved_errno" pattern,
along with returning -1 ourselves instead of "errno". The caller can
thus rely on our "errno" on failure.
See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61846 for a related
bug report against GCC.
1.
trace2/tr2_dst.c: In function ‘tr2_dst_get_trace_fd.part.5’:
trace2/tr2_dst.c:296:10: warning: ‘fd’ may be used uninitialized in this function [-Wmaybe-uninitialized]
dst->fd = fd;
~~~~~~~~^~~~
trace2/tr2_dst.c:229:6: note: ‘fd’ was declared here
int fd;
^~
2. https://lore.kernel.org/git/20200404142131.GA679473@coredump.intra.peff.net/
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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