git@vger.kernel.org list mirror (unofficial, one of many)
 help / color / mirror / code / Atom feed
From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: git@vger.kernel.org
Cc: "Junio C Hamano" <gitster@pobox.com>, "Jeff King" <peff@peff.net>,
	"Denton Liu" <liu.denton@gmail.com>,
	"Jeff Hostetler" <jeffhost@microsoft.com>,
	"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Subject: [PATCH] trace2: refactor to avoid gcc warning under -O3
Date: Wed,  5 May 2021 10:40:32 +0200	[thread overview]
Message-ID: <patch-1.1-87d9bcf1095-20210505T083951Z-avarab@gmail.com> (raw)
In-Reply-To: <20200404142131.GA679473@coredump.intra.peff.net>

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.

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/
---
 trace2/tr2_dst.c | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/trace2/tr2_dst.c b/trace2/tr2_dst.c
index ae052a07fe2..c2aba71041b 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 *saved_errno)
 {
 	int fd;
 	struct sockaddr_un sa;
 
 	fd = socket(AF_UNIX, sock_type, 0);
-	if (fd == -1)
-		return errno;
+	if (fd == -1) {
+		*saved_errno = 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;
+		*saved_errno = errno;
 		close(fd);
-		return e;
+		return -1;
 	}
 
 	*out_fd = fd;
@@ -227,7 +230,7 @@ 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;
 
 	/*
@@ -271,15 +274,15 @@ 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))
 			goto connected;
-		if (e != EPROTOTYPE)
+		if (saved_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,
+					     &saved_errno))
 			goto connected;
 	}
 
@@ -287,7 +290,7 @@ 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;
-- 
2.31.1.745.g2af7c6593ce


  reply	other threads:[~2021-05-05  8:40 UTC|newest]

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-01  7:30 [PATCH] Fix -Wmaybe-uninitialized warnings under -O0 Denton Liu
     [not found] ` <CAPUEspgBkmxszgBee8C9hZnEwqztf-XKEj7LB_jWVFJaJCge0w@mail.gmail.com>
2020-04-01  9:05   ` Denton Liu
2020-04-01  9:52 ` Jeff King
2020-04-01 14:06   ` Denton Liu
2020-04-03 14:04     ` Jeff King
2020-04-03 14:38       ` Jeff King
2020-04-04 12:07       ` Denton Liu
2020-04-04 14:21         ` Jeff King
2021-05-05  8:40           ` Ævar Arnfjörð Bjarmason [this message]
2021-05-05  9:47             ` [PATCH] trace2: refactor to avoid gcc warning under -O3 Junio C Hamano
2021-05-05 13:34               ` Jeff King
2021-05-05 14:38             ` Johannes Schindelin
2021-05-06  1:26               ` Junio C Hamano
2021-05-06 20:29                 ` Johannes Schindelin
2021-05-06 21:10                   ` Junio C Hamano
2021-05-11 14:34                     ` Johannes Schindelin
2021-05-11 18:00                       ` Jeff King
2021-05-11 20:58                         ` Junio C Hamano
2021-05-11 21:07                           ` Jeff King
2021-05-11 21:33                             ` Junio C Hamano
2021-05-11  7:03             ` Junio C Hamano
2021-05-11 13:04             ` [PATCH v2] " Ævar Arnfjörð Bjarmason
2021-05-11 16:40               ` Jeff Hostetler
2021-05-11 17:54               ` Jeff King
2021-05-11 18:08                 ` Jeff King
2021-05-11 21:09                   ` Junio C Hamano
2021-05-20  0:20                   ` Junio C Hamano
2021-05-20 11:05                     ` [PATCH v3] " Ævar Arnfjörð Bjarmason
2021-05-20 13:13                       ` Jeff King
2021-05-20 22:08                         ` Junio C Hamano
2021-05-21  9:34                           ` Jeff King

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: http://vger.kernel.org/majordomo-info.html

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=patch-1.1-87d9bcf1095-20210505T083951Z-avarab@gmail.com \
    --to=avarab@gmail.com \
    --cc=git@vger.kernel.org \
    --cc=gitster@pobox.com \
    --cc=jeffhost@microsoft.com \
    --cc=liu.denton@gmail.com \
    --cc=peff@peff.net \
    --subject='Re: [PATCH] trace2: refactor to avoid gcc warning under -O3' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Code repositories for project(s) associated with this inbox:

	https://80x24.org/mirrors/git.git

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).