* [PATCH 1/2] * avoid gcc 4.4.1 compiler warnings due to ignored write return values
@ 2009-11-23 6:20 Dirk-Jan C. Binnema
2009-11-23 7:34 ` Karl Wiberg
0 siblings, 1 reply; 8+ messages in thread
From: Dirk-Jan C. Binnema @ 2009-11-23 6:20 UTC (permalink / raw)
To: notmuch@notmuchmail org
From: Dirk-Jan C. Binnema <djcb.bulk@gmail.com>
Date: Mon, 23 Nov 2009 08:03:35 +0200
---
notmuch-new.c | 4 +++-
notmuch-tag.c | 4 +++-
2 files changed, 6 insertions(+), 2 deletions(-)
diff --git a/notmuch-new.c b/notmuch-new.c
index a2b30bd..3d04efa 100644
--- a/notmuch-new.c
+++ b/notmuch-new.c
@@ -35,8 +35,10 @@ static volatile sig_atomic_t interrupted;
static void
handle_sigint (unused (int sig))
{
+ ssize_t ignored;
static char msg[] = "Stopping... \n";
- write(2, msg, sizeof(msg)-1);
+
+ ignored = write(2, msg, sizeof(msg)-1);
interrupted = 1;
}
diff --git a/notmuch-tag.c b/notmuch-tag.c
index e2311f6..ec98c3b 100644
--- a/notmuch-tag.c
+++ b/notmuch-tag.c
@@ -25,8 +25,10 @@ static volatile sig_atomic_t interrupted;
static void
handle_sigint (unused (int sig))
{
+ ssize_t ignored;
+
static char msg[] = "Stopping... \n";
- write(2, msg, sizeof(msg)-1);
+ ignored = write(2, msg, sizeof(msg)-1);
interrupted = 1;
}
--
1.6.3.3
^ permalink raw reply related [flat|nested] 8+ messages in thread
* Re: [PATCH 1/2] * avoid gcc 4.4.1 compiler warnings due to ignored write return values
2009-11-23 6:20 [PATCH 1/2] * avoid gcc 4.4.1 compiler warnings due to ignored write return values Dirk-Jan C. Binnema
@ 2009-11-23 7:34 ` Karl Wiberg
2009-11-23 11:11 ` Dirk-Jan Binnema
0 siblings, 1 reply; 8+ messages in thread
From: Karl Wiberg @ 2009-11-23 7:34 UTC (permalink / raw)
To: djcb; +Cc: notmuch@notmuchmail org
On Mon, Nov 23, 2009 at 7:20 AM, Dirk-Jan C. Binnema
<djcb.bulk@gmail.com> wrote:
> + ssize_t ignored;
> static char msg[] = "Stopping... \n";
> - write(2, msg, sizeof(msg)-1);
> +
> + ignored = write(2, msg, sizeof(msg)-1);
> interrupted = 1;
> }
Didn't the "(void)" suggestion work?
--
Karl Wiberg, kha@treskal.com
subrabbit.wordpress.com
www.treskal.com/kalle
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH 1/2] * avoid gcc 4.4.1 compiler warnings due to ignored write return values
2009-11-23 7:34 ` Karl Wiberg
@ 2009-11-23 11:11 ` Dirk-Jan Binnema
2009-11-23 13:19 ` Karl Wiberg
0 siblings, 1 reply; 8+ messages in thread
From: Dirk-Jan Binnema @ 2009-11-23 11:11 UTC (permalink / raw)
To: Karl Wiberg; +Cc: notmuch@notmuchmail org, djcb
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On Mon, Nov 23, 2009 at 9:34 AM, Karl Wiberg <kha@treskal.com> wrote:
> On Mon, Nov 23, 2009 at 7:20 AM, Dirk-Jan C. Binnema
> <djcb.bulk@gmail.com> wrote:
>
> > + ssize_t ignored;
> > static char msg[] = "Stopping... \n";
> > - write(2, msg, sizeof(msg)-1);
> > +
> > + ignored = write(2, msg, sizeof(msg)-1);
> > interrupted = 1;
> > }
>
> Didn't the "(void)" suggestion work?
>
>
I actually preferred that solution, but unfortunately, it didn't stop gcc
from complaining...
Best wishes,
Dirk.
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^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH 1/2] * avoid gcc 4.4.1 compiler warnings due to ignored write return values
2009-11-23 11:11 ` Dirk-Jan Binnema
@ 2009-11-23 13:19 ` Karl Wiberg
2009-11-23 14:24 ` Jed Brown
0 siblings, 1 reply; 8+ messages in thread
From: Karl Wiberg @ 2009-11-23 13:19 UTC (permalink / raw)
To: Dirk-Jan Binnema; +Cc: notmuch@notmuchmail org, djcb
On Mon, Nov 23, 2009 at 12:11 PM, Dirk-Jan Binnema <djcb.bulk@gmail.com> wrote:
> On Mon, Nov 23, 2009 at 9:34 AM, Karl Wiberg <kha@treskal.com> wrote:
>
> > Didn't the "(void)" suggestion work?
>
> I actually preferred that solution, but unfortunately, it didn't
> stop gcc from complaining...
Hmpf. I'd argue that that's a gcc bug, forcing the user to use an
unnecessarily complicated way to pretend to use the return value. Oh
well.
--
Karl Wiberg, kha@treskal.com
subrabbit.wordpress.com
www.treskal.com/kalle
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH 1/2] * avoid gcc 4.4.1 compiler warnings due to ignored write return values
2009-11-23 13:19 ` Karl Wiberg
@ 2009-11-23 14:24 ` Jed Brown
2009-11-23 16:14 ` Dirk-Jan Binnema
2009-12-01 15:57 ` Carl Worth
0 siblings, 2 replies; 8+ messages in thread
From: Jed Brown @ 2009-11-23 14:24 UTC (permalink / raw)
To: Karl Wiberg, Dirk-Jan Binnema; +Cc: notmuch@notmuchmail org, djcb
On Mon, 23 Nov 2009 14:19:18 +0100, Karl Wiberg <kha@treskal.com> wrote:
> On Mon, Nov 23, 2009 at 12:11 PM, Dirk-Jan Binnema <djcb.bulk@gmail.com> wrote:
>
> > On Mon, Nov 23, 2009 at 9:34 AM, Karl Wiberg <kha@treskal.com> wrote:
> >
> > > Didn't the "(void)" suggestion work?
> >
> > I actually preferred that solution, but unfortunately, it didn't
> > stop gcc from complaining...
>
> Hmpf. I'd argue that that's a gcc bug, forcing the user to use an
> unnecessarily complicated way to pretend to use the return value. Oh
> well.
From the gcc man page:
-Wunused-value
Warn whenever a statement computes a result that is explicitly
not used. To suppress this warning cast the unused expression
to void. This includes an expression-statement or the left-
hand side of a comma expression that contains no side effects.
For example, an expression such as x[i,j] will cause a
warning, while x[(void)i,j] will not.
This warning is enabled by -Wall.
But I'm confused here because I don't currently see any warnings with
gcc-4.4.2. Actually this must be a bug because I get no warnings for
the blatantly unused
malloc(5);
with -Wall -Wextra -pedantic. Anyway, if your system headers specify
__attribute__((warn_unused_result)) for write, then you could be running
into this bug/feature
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35579
Jed
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH 1/2] * avoid gcc 4.4.1 compiler warnings due to ignored write return values
2009-11-23 14:24 ` Jed Brown
@ 2009-11-23 16:14 ` Dirk-Jan Binnema
2009-11-23 16:38 ` Jed Brown
2009-12-01 15:57 ` Carl Worth
1 sibling, 1 reply; 8+ messages in thread
From: Dirk-Jan Binnema @ 2009-11-23 16:14 UTC (permalink / raw)
To: Jed Brown; +Cc: notmuch@notmuchmail org, djcb
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Hi Jed,
On Mon, Nov 23, 2009 at 4:24 PM, Jed Brown <jed@59a2.org> wrote:
>
>
> But I'm confused here because I don't currently see any warnings with
> gcc-4.4.2. Actually this must be a bug because I get no warnings for
> the blatantly unused
>
> malloc(5);
>
Did you try it with -O2? Without optimizations many of the warnings are not
issued.
Best wishes,
Dirk.
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^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH 1/2] * avoid gcc 4.4.1 compiler warnings due to ignored write return values
2009-11-23 16:14 ` Dirk-Jan Binnema
@ 2009-11-23 16:38 ` Jed Brown
0 siblings, 0 replies; 8+ messages in thread
From: Jed Brown @ 2009-11-23 16:38 UTC (permalink / raw)
To: Dirk-Jan Binnema, Jed Brown; +Cc: notmuch@notmuchmail org, djcb
On Mon, 23 Nov 2009 18:14:12 +0200, Dirk-Jan Binnema <djcb.bulk@gmail.com> wrote:
> Did you try it with -O2? Without optimizations many of the warnings are not
> issued.
Yes,
$ cat > foo.c
#include <stdlib.h>
#include <unistd.h>
int main()
{
malloc(5);
write(2,0,10);
return 0;
}
$ gcc -static -std=c89 -O0 -Wall -Wextra -pedantic -o foo foo.c
$ objdump -d -M intel foo |grep -A12 '<main>'
00000000004002a4 <main>:
4002a4: 55 push rbp
4002a5: 48 89 e5 mov rbp,rsp
4002a8: bf 05 00 00 00 mov edi,0x5
4002ad: e8 6e 61 00 00 call 406420 <__libc_malloc>
4002b2: ba 0a 00 00 00 mov edx,0xa
4002b7: be 00 00 00 00 mov esi,0x0
4002bc: bf 02 00 00 00 mov edi,0x2
4002c1: e8 ea a0 00 00 call 40a3b0 <__libc_write>
4002c6: b8 00 00 00 00 mov eax,0x0
4002cb: c9 leave
4002cc: c3 ret
4002cd: 90 nop
$ gcc -v
Using built-in specs.
Target: x86_64-unknown-linux-gnu
Configured with: ../configure --prefix=/usr --enable-shared --enable-languages=c,c++,fortran,objc,obj-c++,ada --enable-threads=posix --mandir=/usr/share/man --infodir=/usr/share/info --enable-__cxa_atexit --disable-multilib --libdir=/usr/lib --libexecdir=/usr/lib --enable-clocale=gnu --disable-libstdcxx-pch --with-tune=generic
Thread model: posix
gcc version 4.4.2 (GCC)
$ uname -a
Linux kunyang 2.6.31-ARCH #1 SMP PREEMPT Tue Nov 10 19:01:40 CET 2009 x86_64 Intel(R) Core(TM)2 Duo CPU P8700 @ 2.53GHz GenuineIntel GNU/Linux
Seems fishy.
Jed
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH 1/2] * avoid gcc 4.4.1 compiler warnings due to ignored write return values
2009-11-23 14:24 ` Jed Brown
2009-11-23 16:14 ` Dirk-Jan Binnema
@ 2009-12-01 15:57 ` Carl Worth
1 sibling, 0 replies; 8+ messages in thread
From: Carl Worth @ 2009-12-01 15:57 UTC (permalink / raw)
To: Jed Brown, Karl Wiberg, Dirk-Jan Binnema; +Cc: notmuch@notmuchmail org, djcb
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On Mon, 23 Nov 2009 15:24:46 +0100, Jed Brown <jed@59A2.org> wrote:
> >From the gcc man page:
>
> -Wunused-value
> Warn whenever a statement computes a result that is explicitly
> not used. To suppress this warning cast the unused expression
> to void. This includes an expression-statement or the left-
> hand side of a comma expression that contains no side effects.
> For example, an expression such as x[i,j] will cause a
> warning, while x[(void)i,j] will not.
>
> This warning is enabled by -Wall.
>
> But I'm confused here because I don't currently see any warnings with
> gcc-4.4.2. Actually this must be a bug because I get no warnings for
> the blatantly unused
>
> malloc(5);
I'm guessing that the -Wunused-value warning doesn't consider values
computed by function calls.
> with -Wall -Wextra -pedantic. Anyway, if your system headers specify
> __attribute__((warn_unused_result)) for write, then you could be running
> into this bug/feature
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35579
Yes, this is the attribute that's triggering the warnings. I poked
around in the glibc headers to see how to get this warning myself, and I
finally found:
make CFLAGS="-O -D_FORTIFY_SOURCE"
That makes the warning appear even with gcc 4.3.4, (and the definitions
in the headers suggest it will work with any gcc >= 4.1).
So I've pushed the patch now, (with an updated commit message to reflect
the above analysis).
-Carl
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^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2009-12-01 15:58 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2009-11-23 6:20 [PATCH 1/2] * avoid gcc 4.4.1 compiler warnings due to ignored write return values Dirk-Jan C. Binnema
2009-11-23 7:34 ` Karl Wiberg
2009-11-23 11:11 ` Dirk-Jan Binnema
2009-11-23 13:19 ` Karl Wiberg
2009-11-23 14:24 ` Jed Brown
2009-11-23 16:14 ` Dirk-Jan Binnema
2009-11-23 16:38 ` Jed Brown
2009-12-01 15:57 ` Carl Worth
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