Re: [PATCH] x86/signal: Remove pax argument from restore_sigcontext

[Ingo Molnar <mingo@kernel.org>]

* Brian Gerst <brgerst@gmail.com> wrote:

> The pax argument is unnecesary.  Instead, store the RAX value directly
> in regs.
> 
> Signed-off-by: Brian Gerst <brgerst@gmail.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Andy Lutomirski <luto@amacapital.net>
> Cc: Denys Vlasenko <dvlasenk@redhat.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: x86@kernel.org
> Cc: linux-kernel@vger.kernel.org
> ---
>  arch/x86/ia32/ia32_signal.c        | 17 ++++++-----------
>  arch/x86/include/asm/sighandling.h |  4 +---
>  arch/x86/kernel/signal.c           | 22 ++++++++--------------
>  3 files changed, 15 insertions(+), 28 deletions(-)
> 
> diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
> index 1f5e2b0..c81d35e6 100644
> --- a/arch/x86/ia32/ia32_signal.c
> +++ b/arch/x86/ia32/ia32_signal.c
> @@ -161,8 +161,7 @@ int copy_siginfo_from_user32(siginfo_t *to, compat_siginfo_t __user *from)
>  }
>  
>  static int ia32_restore_sigcontext(struct pt_regs *regs,
> -				   struct sigcontext_ia32 __user *sc,
> -				   unsigned int *pax)
> +				   struct sigcontext_ia32 __user *sc)
>  {
>  	unsigned int tmpflags, err = 0;
>  	void __user *buf;
> @@ -184,7 +183,7 @@ static int ia32_restore_sigcontext(struct pt_regs *regs,
>  		RELOAD_SEG(es);
>  
>  		COPY(di); COPY(si); COPY(bp); COPY(sp); COPY(bx);
> -		COPY(dx); COPY(cx); COPY(ip);
> +		COPY(dx); COPY(cx); COPY(ip); COPY(ax);
>  		/* Don't touch extended registers */
>  
>  		COPY_SEG_CPL3(cs);
> @@ -197,8 +196,6 @@ static int ia32_restore_sigcontext(struct pt_regs *regs,
>  
>  		get_user_ex(tmp, &sc->fpstate);
>  		buf = compat_ptr(tmp);
> -
> -		get_user_ex(*pax, &sc->ax);
>  	} get_user_catch(err);

Note that arch/x86/kernel/signal.c appears to have a similar pattern - 
and there it could be removed as well?

I'm wondering what the original reason for adding the extra handling 
of regs->ax was. Maybe something changed regs->ax - but I cannot find 
such code path anymore.

It would be nice to try to do a bit of Git archeology to figure out 
the origins of this complication - maybe it's something subtle - or 
it's something that has changed meanwhile.

Thanks,

	Ingo