Messages in this thread | | | Date | Tue, 17 Nov 2015 16:44:53 +0000 | From | Will Deacon <> | Subject | Re: next build: 235 warnings 3 failures (next/next-20151117) |
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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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