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Groups > linux.kernel > #1271408
| From | Will Deacon <will.deacon@arm.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: next build: 235 warnings 3 failures (next/next-20151117) |
| Date | 2015-11-17 17:50 +0100 |
| Message-ID | <qvRC9-7wq-3@gated-at.bofh.it> (permalink) |
| References | <qvKhk-2Hb-21@gated-at.bofh.it> <qvKhk-2Hb-19@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
Hi Arnd,
On Tue, Nov 17, 2015 at 09:57:30AM +0100, Arnd Bergmann wrote:
> On Monday 16 November 2015 19:05:05 Olof's autobuilder wrote:
> >
> > Errors:
> >
> > arm64.allmodconfig:
> > arch/arm64/include/asm/barrier.h:71:3: error: read-only variable '___p1' used as 'asm' output
> > arch/arm64/include/asm/barrier.h:75:3: error: read-only variable '___p1' used as 'asm' output
> > arch/arm64/include/asm/barrier.h:79:3: error: read-only variable '___p1' used as 'asm' output
> > arch/arm64/include/asm/barrier.h:83:3: error: read-only variable '___p1' used as 'asm' output
> > arch/arm64/include/asm/barrier.h:71:3: error: read-only variable '___p1' used as 'asm' output
> > arch/arm64/include/asm/barrier.h:75:3: error: read-only variable '___p1' used as 'asm' output
> > arch/arm64/include/asm/barrier.h:79:3: error: read-only variable '___p1' used as 'asm' output
> > arch/arm64/include/asm/barrier.h:83:3: error: read-only variable '___p1' used as 'asm' output
> > arch/arm64/include/asm/barrier.h:71:3: error: read-only variable '___p1' used as 'asm' output
>
> The patch below seems to fix it. Please review/apply.
>
> 8<----
> Subject: ARM64: make smp_load_acquire() work with const arguments
>
> smp_load_acquire() uses typeof() to declare a local variable for temporarily
> storing the output of the memory access. This fails when the argument is
> constant, because the assembler complains about using a constant register
> as output:
>
> arch/arm64/include/asm/barrier.h:71:3: error: read-only variable '___p1'
> used as 'asm' output
Do you know the usage in the kernel causing this warning?
> This changes the implementation to use an 'unsigned long' for the temporary value
> and only cast it to the original type in the end.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
> index 624f9679f4b0..05fa329467f6 100644
> --- a/arch/arm64/include/asm/barrier.h
> +++ b/arch/arm64/include/asm/barrier.h
> @@ -64,7 +64,7 @@ do { \
>
> #define smp_load_acquire(p) \
> ({ \
> - typeof(*p) ___p1; \
> + unsigned long ___p1; \
> compiletime_assert_atomic_type(*p); \
> switch (sizeof(*p)) { \
> case 1: \
> @@ -84,7 +84,7 @@ do { \
> : "=r" (___p1) : "Q" (*p) : "memory"); \
> break; \
> } \
> - ___p1; \
> + (typeof(*p))___p1; \
My worry about having the cast here is if somebody decides to
smp_load_acquire from a packed 64-bit structure (e.g. some sort of lock),
then we'll get a conversion to non-scalar type error from the compiler.
Will
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Re: next build: 235 warnings 3 failures (next/next-20151117) Arnd Bergmann <arnd@arndb.de> - 2015-11-17 10:00 +0100
Re: next build: 235 warnings 3 failures (next/next-20151117) Will Deacon <will.deacon@arm.com> - 2015-11-17 17:50 +0100
Re: next build: 235 warnings 3 failures (next/next-20151117) Eric Dumazet <eric.dumazet@gmail.com> - 2015-11-17 18:10 +0100
Re: next build: 235 warnings 3 failures (next/next-20151117) Arnd Bergmann <arnd@arndb.de> - 2015-11-17 18:10 +0100
Re: next build: 235 warnings 3 failures (next/next-20151117) Will Deacon <will.deacon@arm.com> - 2015-11-17 18:20 +0100
Re: next build: 235 warnings 3 failures (next/next-20151117) Arnd Bergmann <arnd@arndb.de> - 2015-11-17 20:20 +0100
Re: next build: 235 warnings 3 failures (next/next-20151117) Will Deacon <will.deacon@arm.com> - 2015-11-18 11:20 +0100
RE: next build: 235 warnings 3 failures (next/next-20151117) David Laight <David.Laight@ACULAB.COM> - 2015-11-18 13:20 +0100
Re: next build: 235 warnings 3 failures (next/next-20151117) Will Deacon <will.deacon@arm.com> - 2015-11-18 13:30 +0100
RE: next build: 235 warnings 3 failures (next/next-20151117) David Laight <David.Laight@ACULAB.COM> - 2015-11-18 16:30 +0100
Re: next build: 235 warnings 3 failures (next/next-20151117) Will Deacon <will.deacon@arm.com> - 2015-11-18 16:40 +0100
RE: next build: 235 warnings 3 failures (next/next-20151117) David Laight <David.Laight@ACULAB.COM> - 2015-11-18 17:00 +0100
RE: next build: 235 warnings 3 failures (next/next-20151117) David Laight <David.Laight@ACULAB.COM> - 2015-11-18 11:30 +0100
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