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trace2: refactor to avoid gcc warning under -O3

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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>
This commit is contained in:
Ævar Arnfjörð Bjarmason 2021-05-20 13:05:45 +02:00 committed by Junio C Hamano
parent c753e2a7a8
commit 4e0a64a713
1 changed files with 8 additions and 10 deletions
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18
trace2/tr2_dst.c
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@ -115,15 +115,16 @@ static int tr2_dst_try_uds_connect(const char *path, int sock_type, int *out_fd)
fd = socket(AF_UNIX, sock_type, 0);
if (fd == -1)
return errno;
return -1;
sa.sun_family = AF_UNIX;
strlcpy(sa.sun_path, path, sizeof(sa.sun_path));
if (connect(fd, (struct sockaddr *)&sa, sizeof(sa)) == -1) {
int e = errno;
int saved_errno = errno;
close(fd);
return e;
errno = saved_errno;
return -1;
}
*out_fd = fd;
@ -138,7 +139,6 @@ static int tr2_dst_try_unix_domain_socket(struct tr2_dst *dst,
{
unsigned int uds_try = 0;
int fd;
int e;
const char *path = NULL;
/*
@ -182,15 +182,13 @@ static int tr2_dst_try_unix_domain_socket(struct tr2_dst *dst,
}
if (uds_try & TR2_DST_UDS_TRY_STREAM) {
e = tr2_dst_try_uds_connect(path, SOCK_STREAM, &fd);
if (!e)
if (!tr2_dst_try_uds_connect(path, SOCK_STREAM, &fd))
goto connected;
if (e != EPROTOTYPE)
if (errno != EPROTOTYPE)
goto error;
}
if (uds_try & TR2_DST_UDS_TRY_DGRAM) {
e = tr2_dst_try_uds_connect(path, SOCK_DGRAM, &fd);
if (!e)
if (!tr2_dst_try_uds_connect(path, SOCK_DGRAM, &fd))
goto connected;
}
@ -198,7 +196,7 @@ error:
if (tr2_dst_want_warning())
warning("trace2: could not connect to socket '%s' for '%s' tracing: %s",
path, tr2_sysenv_display_name(dst->sysenv_var),
strerror(e));
strerror(errno));
tr2_dst_trace_disable(dst);
return 0;