From: Jeff King <peff@peff.net>
To: git@vger.kernel.org
Cc: Jonathan Nieder <jrnieder@gmail.com>
Subject: [PATCH] silence gcc array-bounds warning
Date: Fri, 4 Oct 2013 03:52:35 -0400 [thread overview]
Message-ID: <20131004075234.GA26068@sigill.intra.peff.net> (raw)
In shorten_unambiguous_ref, we build and cache a reverse-map of the
rev-parse rules like this:
static char **scanf_fmts;
static int nr_rules;
if (!nr_rules) {
for (; ref_rev_parse_rules[nr_rules]; nr_rules++)
... generate scanf_fmts ...
}
where ref_rev_parse_rules is terminated with a NULL pointer.
Compiling with "gcc -O2 -Wall" does not cause any problems, but
compiling with "-O3 -Wall" generates:
$ make CFLAGS='-O3 -Wall' refs.o
refs.c: In function ‘shorten_unambiguous_ref’:
refs.c:3379:29: warning: array subscript is above array bounds [-Warray-bounds]
for (; ref_rev_parse_rules[nr_rules]; nr_rules++)
Curiously, we can silence this by explicitly nr_rules to 0
in the beginning of the loop, even though the compiler
should be able to tell that we follow this code path only
when nr_rules is already 0.
Signed-off-by: Jeff King <peff@peff.net>
---
I've convinced myself that this is a gcc bug and not some weird
undefined behavior or extra analysis that gcc can do due to inlined
functions. The fact that what should be a noop makes the warning go away
makes me very suspicious.
You can also silence it by declaring ref_rev_parse_rules as:
const char * const ref_rev_parse_rules[];
to make both the strings themselves and the pointers in the list
constant. And that may be worth doing instead, because it really is
a constant list for us. The downside is that it's a little uglier to
read, and it carries over to pointers we use to access it, like:
const char * const *p;
for (p = ref_rev_parse_rules; *p; p++)
...
refs.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/refs.c b/refs.c
index ad5d66c..c1cc98a 100644
--- a/refs.c
+++ b/refs.c
@@ -3376,7 +3376,7 @@ char *shorten_unambiguous_ref(const char *refname, int strict)
size_t total_len = 0;
/* the rule list is NULL terminated, count them first */
- for (; ref_rev_parse_rules[nr_rules]; nr_rules++)
+ for (nr_rules = 0; ref_rev_parse_rules[nr_rules]; nr_rules++)
/* no +1 because strlen("%s") < strlen("%.*s") */
total_len += strlen(ref_rev_parse_rules[nr_rules]);
--
1.8.4.1.4.gf327177
next reply other threads:[~2013-10-04 7:52 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-04 7:52 Jeff King [this message]
-- strict thread matches above, loose matches on Subject: below --
2013-10-24 8:45 [PATCH] silence gcc array-bounds warning 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=20131004075234.GA26068@sigill.intra.peff.net \
--to=peff@peff.net \
--cc=git@vger.kernel.org \
--cc=jrnieder@gmail.com \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public 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).