[U-Boot] [PATCH] arm, ubifs: fix gcc5.x compiler warning

[Tom Rini <trini@konsulko.com>]

On Mon, Nov 30, 2015 at 11:03:53AM +0100, Heiko Schocher wrote:
> Hello Jeroen,
> 
> Am 30.11.2015 um 10:20 schrieb Jeroen Hofstee:
> >Hello Heiko,
> >
> >On 30-11-15 08:47, Heiko Schocher wrote:
> >>compiling U-Boot for openrd_base_defconfig with
> >>gcc 5.x shows the following warning:
> >>
> >>   CC      fs/ubifs/super.o
> >>In file included from fs/ubifs/ubifs.h:35:0,
> >>                  from fs/ubifs/super.c:37:
> >>fs/ubifs/super.c: In function 'atomic_inc':
> >>./arch/arm/include/asm/atomic.h:55:2: warning: 'flags' is used uninitialized in this function
> >>[-Wuninitialized]
> >>   local_irq_save(flags);
> >>   ^
> >>fs/ubifs/super.c: In function 'atomic_dec':
> >>./arch/arm/include/asm/atomic.h:64:2: warning: 'flags' is used uninitialized in this function
> >>[-Wuninitialized]
> >>   local_irq_save(flags);
> >>   ^
> >>   CC      fs/ubifs/sb.o
> >>[...]
> >>   CC      fs/ubifs/lpt.o
> >>In file included from include/linux/bitops.h:123:0,
> >>                  from include/common.h:20,
> >>                  from include/ubi_uboot.h:17,
> >>                  from fs/ubifs/ubifs.h:37,
> >>                  from fs/ubifs/lpt.c:35:
> >>fs/ubifs/lpt.c: In function 'test_and_set_bit':
> >>./arch/arm/include/asm/bitops.h:57:2: warning: 'flags' is used uninitialized in this function
> >>[-Wuninitialized]
> >>   local_irq_save(flags);
> >>   ^
> >>   CC      fs/ubifs/lpt_commit.o
> >>In file included from include/linux/bitops.h:123:0,
> >>                  from include/common.h:20,
> >>                  from include/ubi_uboot.h:17,
> >>                  from fs/ubifs/ubifs.h:37,
> >>                  from fs/ubifs/lpt_commit.c:26:
> >>fs/ubifs/lpt_commit.c: In function 'test_and_set_bit':
> >>./arch/arm/include/asm/bitops.h:57:2: warning: 'flags' is used uninitialized in this function
> >>[-Wuninitialized]
> >>   local_irq_save(flags);
> >>   ^
> >>   CC      fs/ubifs/scan.o
> >>   CC      fs/ubifs/lprops.o
> >>   CC      fs/ubifs/tnc.o
> >>In file included from include/linux/bitops.h:123:0,
> >>                  from include/common.h:20,
> >>                  from include/ubi_uboot.h:17,
> >>                  from fs/ubifs/ubifs.h:37,
> >>                  from fs/ubifs/tnc.c:30:
> >>fs/ubifs/tnc.c: In function 'test_and_set_bit':
> >>./arch/arm/include/asm/bitops.h:57:2: warning: 'flags' is used uninitialized in this function
> >>[-Wuninitialized]
> >>   local_irq_save(flags);
> >>   ^
> >>   CC      fs/ubifs/tnc_misc.o
> >>
> >>Fix it.
> >>
> >>Signed-off-by: Heiko Schocher <hs@denx.de>
> >>---
> >>
> >>  arch/arm/include/asm/atomic.h | 14 +++++++-------
> >>  arch/arm/include/asm/bitops.h |  4 ++--
> >>  2 files changed, 9 insertions(+), 9 deletions(-)
> >>
> >>diff --git a/arch/arm/include/asm/atomic.h b/arch/arm/include/asm/atomic.h
> >>index 34c07fe..9b79506 100644
> >>--- a/arch/arm/include/asm/atomic.h
> >>+++ b/arch/arm/include/asm/atomic.h
> >>@@ -32,7 +32,7 @@ typedef struct { volatile int counter; } atomic_t;
> >>  static inline void atomic_add(int i, volatile atomic_t *v)
> >>  {
> >>-    unsigned long flags;
> >>+    unsigned long flags = 0;
> >>      local_irq_save(flags);
> >>      v->counter += i;
> >>@@ -41,7 +41,7 @@ static inline void atomic_add(int i, volatile atomic_t *v)
> >
> >Since flags is an "out" argument, something else must be wrong.
> >There should be no need to initialize it, since local_irq_save should
> >do that afaik.
> 
> yes, you are right, it should be, but gcc 5.x seems to have problems
> with it ... compiled code size for the openrd_base config is same with
> my patch ...
> 
> Hmm... for the openrd_base compile local_irq_save() is used from:
> arch/arm/thumb1/include/asm/proc-armv/system.h
> 
> with:
> static inline void local_irq_save(
>         unsigned long flags __attribute__((unused)))
> {
>         __asm__ __volatile__ ("" : : : "memory");
> }
> 
> flasg marked as unused ... seems correct to me, but I have
> no idea, why gcc 5.x prints a warning ... any ideas?

Well, gcc does get more vigerous in its checking now and yeah, it feels
like it's flagging false positives.   In this case I think the answer is
that we need to nop out the various calls a bit harder on ARM.  Glancing
at the kernel, I think for thumb1 we should just do what we do for
non-thumb, or translate that into thumb1 only code.

-- 
Tom
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