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 ee4512ed481 (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 it as suggested in that analysis. We now return -1 ourselves on error, and save away the value of errno in a variable the caller passes in. 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@xxxxxxxxxxxxxxxxxxxxxxx/ Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx> --- On Tue, May 11 2021, Junio C Hamano wrote: > What's the concensus if any on this topic? Having read Johannes's comments I think it's still most readable to just return -1 unconditionally. The resulting code isn't weird, I'd argue that it's a better pattern to save away errno like this, but the commit messages notes that we're working around a GCC bug. > In any case, this needs to be signed off before it gets carved into > our history. Done, and also changed the variable name to minimize the size of the diff. A shorter name allowed for less re-flowing of lines. Range-diff against v1: 1: 87d9bcf1095 ! 1: 782555daade trace2: refactor to avoid gcc warning under -O3 @@ Commit message error, and save away the value of errno in a variable the caller passes in. + 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’: @@ Commit message ^~ 2. https://lore.kernel.org/git/20200404142131.GA679473@xxxxxxxxxxxxxxxxxxxxxxx/ + Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx> + ## trace2/tr2_dst.c ## @@ trace2/tr2_dst.c: static int tr2_dst_try_path(struct tr2_dst *dst, const char *tgt_value) #define PREFIX_AF_UNIX_STREAM "af_unix:stream:" @@ trace2/tr2_dst.c: static int tr2_dst_try_path(struct tr2_dst *dst, const char *t -static int tr2_dst_try_uds_connect(const char *path, int sock_type, int *out_fd) +static int tr2_dst_try_uds_connect(const char *path, int sock_type, -+ int *out_fd, int *saved_errno) ++ int *out_fd, int *e) { int fd; struct sockaddr_un sa; @@ trace2/tr2_dst.c: static int tr2_dst_try_path(struct tr2_dst *dst, const char *t - if (fd == -1) - return errno; + if (fd == -1) { -+ *saved_errno = errno; ++ *e = errno; + return -1; + } @@ trace2/tr2_dst.c: static int tr2_dst_try_path(struct tr2_dst *dst, const char *t if (connect(fd, (struct sockaddr *)&sa, sizeof(sa)) == -1) { - int e = errno; -+ *saved_errno = errno; ++ *e = errno; close(fd); - return e; + return -1; } *out_fd = fd; -@@ trace2/tr2_dst.c: static int tr2_dst_try_unix_domain_socket(struct tr2_dst *dst, - { - unsigned int uds_try = 0; - int fd; -- int e; -+ int saved_errno; - const char *path = NULL; - - /* @@ trace2/tr2_dst.c: 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, -+ &saved_errno)) ++ if (!tr2_dst_try_uds_connect(path, SOCK_STREAM, &fd, &e)) goto connected; -- if (e != EPROTOTYPE) -+ if (saved_errno != EPROTOTYPE) + if (e != 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, -+ &saved_errno)) ++ if (!tr2_dst_try_uds_connect(path, SOCK_DGRAM, &fd, &e)) goto connected; } -@@ trace2/tr2_dst.c: static int tr2_dst_try_unix_domain_socket(struct tr2_dst *dst, - 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(saved_errno)); - - tr2_dst_trace_disable(dst); - return 0; trace2/tr2_dst.c | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-) diff --git a/trace2/tr2_dst.c b/trace2/tr2_dst.c index ae052a07fe2..a44fe6b73e0 100644 --- a/trace2/tr2_dst.c +++ b/trace2/tr2_dst.c @@ -197,22 +197,25 @@ static int tr2_dst_try_path(struct tr2_dst *dst, const char *tgt_value) #define PREFIX_AF_UNIX_STREAM "af_unix:stream:" #define PREFIX_AF_UNIX_DGRAM "af_unix:dgram:" -static int tr2_dst_try_uds_connect(const char *path, int sock_type, int *out_fd) +static int tr2_dst_try_uds_connect(const char *path, int sock_type, + int *out_fd, int *e) { int fd; struct sockaddr_un sa; fd = socket(AF_UNIX, sock_type, 0); - if (fd == -1) - return errno; + if (fd == -1) { + *e = 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; + *e = errno; close(fd); - return e; + return -1; } *out_fd = fd; @@ -271,15 +274,13 @@ 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, &e)) goto connected; if (e != 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, &e)) goto connected; } -- 2.31.1.909.g789bb6d90e
