linux-kernel - Re: [GIT PULL] core/locking changes for v3.1

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Date:	Mon, 25 Jul 2011 22:02:04 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaud Lacombe <lacombar@...il.com>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] core/locking changes for v3.1

* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Mon, Jul 25, 2011 at 12:04 PM, Ingo Molnar <mingo@...e.hu> wrote:
> > ..
> > net/netfilter/nf_conntrack_core.c: In function ‘nf_conntrack_init’:
> > net/netfilter/nf_conntrack_core.c:1579:3: warning: the comparison
> > will always evaluate as ‘true’ for the address of
> > ‘nf_conntrack_attach’ will never be NULL [-Waddress]
> 
> These all seem to be essentially compiler bugs.
> 
> We have macros that do generic things (in this case
> "rcu_assign_pointer()" and tests their values. The fact that the tests
> sometimes end up being statically true (or false) is not something the
> compiler should complain about - it should use it to optimize the
> code.
> 
> Sad.
> 
> We can make a compiler bug-report, or disable -Waddress. Or maybe we
> can write the tests in a way that doesn't trigger the compiler bug.
> 
> This same issue is why I hated -Wsign-compare. Some of the things 
> gcc complained about were just technically moronic. So compiler 
> warnings are not always a good thing.

With -Wno-address added (see the first patch below) it looks a lot 
more useful:

aldebaran:~/linux/linux> make -j32 >e
sound/pci/hda/patch_sigmatel.c: In function ‘stac92xx_init’:
sound/pci/hda/patch_sigmatel.c:4385:3: warning: statement with no 
effect [-Wunused-value]
sound/pci/hda/patch_sigmatel.c: In function ‘stac92xx_resume’:
sound/pci/hda/patch_sigmatel.c:4925:3: warning: statement with no 
effect [-Wunused-value]
sound/pci/hda/patch_realtek.c: In function ‘alc_init’:
sound/pci/hda/patch_realtek.c:4176:2: warning: statement with no 
effect [-Wunused-value]
sound/pci/hda/patch_realtek.c: In function ‘alc_resume’:
sound/pci/hda/patch_realtek.c:4558:2: warning: statement with no 
effect [-Wunused-value]
sound/pci/hda/hda_codec.c: In function 
‘snd_hda_mixer_amp_switch_put’:
sound/pci/hda/hda_codec.c:2320:2: warning: statement with no effect 
[-Wunused-value]
sound/pci/hda/patch_realtek.c: In function ‘alc269_resume’:
sound/pci/hda/patch_realtek.c:14878:2: warning: statement with no 
effect [-Wunused-value]
drivers/md/dm.c: In function ‘split_bvec’:
drivers/md/dm.c:1052:3: warning: statement with no effect 
[-Wunused-value]
drivers/md/dm.c: In function ‘clone_bio’:
drivers/md/dm.c:1079:3: warning: statement with no effect 
[-Wunused-value]
drivers/md/dm-table.c: In function ‘dm_table_set_integrity’:
drivers/md/dm-table.c:1193:2: warning: statement with no effect 
[-Wunused-value]
Setup is 15260 bytes (padded to 15360 bytes).
System is 4654 kB
CRC 6d1b94ea

those unused-x warnings seem legit and should be fixed. For example 
the second patch below fixed the dm.c warnings.

That's with:

  gcc version 4.6.0 20110509 (Red Hat 4.6.0-7) (GCC)

so a reasonably recent GCC. I think we should kill -Waddress.

Thanks,

	Ingo

diff --git a/Makefile b/Makefile
index d018956..e651294 100644
--- a/Makefile
+++ b/Makefile
@@ -559,9 +559,9 @@ endif # $(dot-config)
 all: vmlinux

 ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
-KBUILD_CFLAGS	+= -Os
+KBUILD_CFLAGS	+= -Os -Wno-address
 else
-KBUILD_CFLAGS	+= -O2
+KBUILD_CFLAGS	+= -O2 -Wno-address
 endif

 include $(srctree)/arch/$(SRCARCH)/Makefile

diff --git a/include/linux/bio.h b/include/linux/bio.h
index ce33e68..283250a 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -527,7 +527,7 @@ extern void bio_integrity_init(void);
 #define bioset_integrity_create(a, b)	(0)
 #define bio_integrity_prep(a)		(0)
 #define bio_integrity_enabled(a)	(0)
-#define bio_integrity_clone(a, b, c, d)	(0)
+#define bio_integrity_clone(a, b, c, d)	({0;})
 #define bioset_integrity_free(a)	do { } while (0)
 #define bio_integrity_free(a, b)	do { } while (0)
 #define bio_integrity_endio(a, b)	do { } while (0)
--
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