[email protected] writes: > From: Behan Webster <[email protected]> > > The existing code uses named registers to get the value of the stack pointer. > The new current_stack_pointer macro is more readable and allows for a central > portable implementation of how to get the stack pointer with ASM. This change > supports being able to compile the kernel with both gcc and Clang. > > Signed-off-by: Mark Charlebois <[email protected]> > Signed-off-by: Behan Webster <[email protected]> > Reviewed-by: Jan-Simon Möller <[email protected]> > --- > arch/arm/include/asm/percpu.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/arm/include/asm/percpu.h b/arch/arm/include/asm/percpu.h > index 209e650..629a975 100644 > --- a/arch/arm/include/asm/percpu.h > +++ b/arch/arm/include/asm/percpu.h > @@ -30,14 +30,14 @@ static inline void set_my_cpu_offset(unsigned long off) > static inline unsigned long __my_cpu_offset(void) > { > unsigned long off; > - register unsigned long *sp asm ("sp"); > + unsigned long sp = current_stack_pointer; > > /* > * Read TPIDRPRW. > * We want to allow caching the value, so avoid using volatile and > * instead use a fake stack read to hazard against barrier(). > */ > - asm("mrc p15, 0, %0, c13, c0, 4" : "=r" (off) : "Q" (*sp)); > + asm("mrc p15, 0, %0, c13, c0, 4" : "=r" (off) : "Q" (sp));
This doesn't do quite the same thing. The existing code pretends to read something from the stack in order to create a barrier of some sort. Your new code stores the value of the stack pointer to a location on the stack for consumption by the "Q" memory constraint. This store is not necessary and should preferably be avoided. -- Måns Rullgård [email protected] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
