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From: Michael Ellerman <mpe@ellerman.id.au>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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 14:41:05 +1000	[thread overview]
Message-ID: <1437108065.29389.6.camel@ellerman.id.au> (raw)
In-Reply-To: <1437086432.28088.46.camel@kernel.crashing.org>

On Fri, 2015-07-17 at 08:40 +1000, Benjamin Herrenschmidt wrote:
> 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 ?

No.

I'm not going to bother measuring it :)

> 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 ...

Yeah true.

There is an "invariant" in that entry code that r9 contains pt_regs, you can
see for example the DTL code goes to pains to ensure it puts pt_regs back in r9
after it clobbers it. As does the current syscall_dotrace.

But looking closer I don't see where we actually use that (prior to this
patch).

So yeah I'll drop this and send a clean up to just get rid of all the r9
reloading.

cheers

      reply	other threads:[~2015-07-17  4:41 UTC|newest]

Thread overview: 20+ 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 ` [RFC PATCH 01/12] powerpc/kernel: Get pt_regs from r9 before calling do_syscall_trace_enter() Benjamin Herrenschmidt
2015-07-17  4:41   ` Michael Ellerman [this message]

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