Re: [PATCH] Fix atomic_arch.h for MIPS32 R6

["dalias@libc.org" <dalias@libc.org>]

On Mon, Mar 21, 2016 at 06:03:47AM +0000, Jaydeep Patil wrote:
> Hi Rich,
> 
> The arch/mips/atomic_arch.h uses MIPS2 opcode for LL and SC
> instructions. Opcodes of these instructions differ on MIPSR6.

Does this mean MIPSR6 is an incompatible ISA that can't run normal
MIPS binaries? If so that's a messy situation we need to find a way to
deal with; if the difference is just LLSC though then perhaps the
kernel's emulation handles it (albeit very slowly).

It would be helpful if you could provide a link to the documentation
of this issue (different opcodes).

> Refer to https://github.com/JaydeepIMG/musl-1/tree/fix_atomic_for_MIPS32_R6 for the patch.
> 
> >From 63428cfc5dfa75d2771ba8205067c438942e1a60 Mon Sep 17 00:00:00 2001
> From: Jaydeep Patil <jaydeep.patil@imgtec.com>
> Date: Mon, 21 Mar 2016 06:00:39 +0000
> Subject: [PATCH] Fix for opcodes of LL/SC instructions for MIPSR6
> 
> ---
> arch/mips/atomic_arch.h | 8 ++++++++
> 1 file changed, 8 insertions(+)
> 
> diff --git a/arch/mips/atomic_arch.h b/arch/mips/atomic_arch.h
> index ce2823b..16b1542 100644
> --- a/arch/mips/atomic_arch.h
> +++ b/arch/mips/atomic_arch.h
> @@ -3,9 +3,13 @@ static inline int a_ll(volatile int *p)
> {
>         int v;
>         __asm__ __volatile__ (
> +#if __mips_isa_rev < 6
>                 ".set push ; .set mips2\n\t"
> +#endif
>                 "ll %0, %1"
> +#if __mips_isa_rev < 6
>                 "\n\t.set pop"
> +#endif

I think just the .set mips2 could be inside #ifdef with the push/pop
always used; that produces less #ifdef clutter. But first we need to
figure out the above issues.

Rich