Re: [PATCH 02/16] powerpc: override __ALIGN() and __ALIGN_STR() macros

[Sathvika Vasireddy]

Hi Christophe,

On 10/08/22 14:01, Christophe Leroy wrote:
> Le 08/08/2022 à 13:48, Sathvika Vasireddy a écrit :
> > Since we need an alignment of 4 bytes, override
> > __ALIGN() and __ALIGN_STR() accordingly.
> Why/When do we now need an alignment of 4 bytes ? Please explain the
> reason in the commit message.
Powerpc instructions must be word-aligned. Currently, there is an 
alignment of 16 bytes (by default),
and it is much more than what is required for powerpc (4 bytes).

The default expansion of these macros are:
#define __ALIGN        .align 4,0x90
#define __ALIGN_STR    ".align 4,0x90"

Since Powerpc Linux does not require a 16 byte alignment, override 
_ALIGN() and __ALIGN_STR() macros
to use required 4 byte alignment.

Sure, I'll explain the reason in commit message.
> > Signed-off-by: Sathvika Vasireddy <sv@xxxxxxxxxxxxx>
> > ---
> >    arch/powerpc/include/asm/linkage.h | 4 ++++
> >    1 file changed, 4 insertions(+)
> >
> > diff --git a/arch/powerpc/include/asm/linkage.h b/arch/powerpc/include/asm/linkage.h
> > index b71b9582e754..8df88fe61438 100644
> > --- a/arch/powerpc/include/asm/linkage.h
> > +++ b/arch/powerpc/include/asm/linkage.h
> > @@ -2,8 +2,12 @@
> >    #ifndef _ASM_POWERPC_LINKAGE_H
> >    #define _ASM_POWERPC_LINKAGE_H
> >    
> > +#include <linux/stringify.h>
> >    #include <asm/types.h>
> >    
> > +#define __ALIGN			.align 2
> > +#define __ALIGN_STR		__stringify(__ALIGN)
> Why do you need to use __stringify ?
>
> ARM64 does:
>
> #define __ALIGN		.align 2
> #define __ALIGN_STR	".align 2"
We could use either __stringify() or quotes, both do the same thing.
While arm64 does ".align 2",

x86 does:
#define __ALIGN         .p2align 4, 0x90
#define __ALIGN_STR     __stringify(__ALIGN)
> > +
> >    #ifdef CONFIG_PPC64_ELF_ABI_V1
> >    #define cond_syscall(x) \
> >    	asm ("\t.weak " #x "\n\t.set " #x ", sys_ni_syscall\n"		\

Thanks for reviewing!

- Sathvika