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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@ozlabs.org, wad@chromium.org, keescook@chromium.org,
	linux-kernel@vger.kernel.org, luto@amacapital.net,
	strosake@linux.vnet.ibm.com, bogdan.purcareata@freescale.com
Subject: Re: [RFC PATCH 01/12] powerpc/kernel: Get pt_regs from r9 before calling do_syscall_trace_enter()
Date: Fri, 17 Jul 2015 08:40:32 +1000	[thread overview]
Message-ID: <1437086432.28088.46.camel@kernel.crashing.org> (raw)
In-Reply-To: <1436945834-26660-1-git-send-email-mpe@ellerman.id.au>

On Wed, 2015-07-15 at 17:37 +1000, Michael Ellerman wrote:
> To call do_syscall_trace_enter() we need pt_regs in r3, but we don't need
> to recalculate it based on r1, it's already in r9.
> 
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

Is there any performance difference ?

I find the addi a bit more robust in case the code gets moved around or
the "previous" code gets changed to either not use r9 or clobber it,
which would have the potential to
introduce a subtle bug ...

Ben.

> ---
>  arch/powerpc/kernel/entry_64.S | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
> index 579e0f9a2d57..0796c487d3db 100644
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -243,7 +243,9 @@ syscall_error:
>  /* Traced system call support */
>  syscall_dotrace:
>  	bl	save_nvgprs
> -	addi	r3,r1,STACK_FRAME_OVERHEAD
> +
> +	/* Get pt_regs into r3 */
> +	mr	r3, r9
>  	bl	do_syscall_trace_enter
>  	/*
>  	 * Restore argument registers possibly just changed.



  parent reply	other threads:[~2015-07-16 22:41 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-07-15  7:37 [RFC PATCH 01/12] powerpc/kernel: Get pt_regs from r9 before calling do_syscall_trace_enter() Michael Ellerman
2015-07-15  7:37 ` [RFC PATCH 02/12] powerpc/kernel: Switch to using MAX_ERRNO Michael Ellerman
2015-07-16 22:42   ` Benjamin Herrenschmidt
2015-07-15  7:37 ` [RFC PATCH 03/12] powerpc/kernel: Change the do_syscall_trace_enter() API Michael Ellerman
2015-07-15  7:37 ` [RFC PATCH 04/12] powerpc: Drop unused syscall_get_error() Michael Ellerman
2015-07-15  7:37 ` [RFC PATCH 05/12] powerpc: Don't negate error in syscall_set_return_value() Michael Ellerman
2015-07-15  7:37 ` [RFC PATCH 06/12] powerpc: Rework syscall_get_arguments() so there is only one loop Michael Ellerman
2015-07-15  7:37 ` [RFC PATCH 07/12] powerpc: Use orig_gpr3 in syscall_get_arguments() Michael Ellerman
2015-07-15  7:37 ` [RFC PATCH 08/12] powerpc: Change syscall_get_nr() to return int Michael Ellerman
2015-07-15  7:37 ` [RFC PATCH 09/12] powerpc/kernel: Add SIG_SYS support for compat tasks Michael Ellerman
2015-07-15 15:12   ` Kees Cook
2015-07-16  3:38     ` Michael Ellerman
2015-07-15  7:37 ` [RFC PATCH 10/12] powerpc/kernel: Enable seccomp filter Michael Ellerman
2015-07-15  7:37 ` [RFC PATCH 11/12] selftests/seccomp: Make seccomp tests work on big endian Michael Ellerman
2015-07-15 15:16   ` Kees Cook
2015-07-16  3:41     ` Michael Ellerman
2015-07-15  7:37 ` [RFC PATCH 12/12] selftests/seccomp: Add powerpc support Michael Ellerman
2015-07-15 15:16   ` Kees Cook
2015-07-16 22:40 ` Benjamin Herrenschmidt [this message]
2015-07-17  4:41   ` [RFC PATCH 01/12] powerpc/kernel: Get pt_regs from r9 before calling do_syscall_trace_enter() Michael Ellerman
2015-07-17  4:41     ` Michael Ellerman

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