Re: [Qemu-devel] [PATCH 01/13] target/arm: Add ARM_FEATURE_SWP

[Peter Maydell]

On 16 September 2018 at 16:53, Richard Henderson
<address@hidden> wrote:
> Ah, I did not know about SWP_EMULATE.  It appears to be
> specific to armv7+ (though we don't support the pre-v4
> cpus for which it might otherwise be relevant).
>
> It does appear that HWCAP_SWP is advertised anyway:
>
> mm/proc-v7.S:   .long   HWCAP_SWP | HWCAP_HALF | HWCAP_THUMB | HWCAP_FAST_MULT

I just discovered that that is overridden by
arch/arm/kernel/setup.c:elf_hwcap_fixup(), which looks at the
ID registers and suppresses HWCAP_SWP if LDREX/STREX and LDREXB/STREXB
are supported.

(Compat 32-bit support in a 64-bit kernel never advertises
HWCAP_SWP.)

thanks
-- PMM