From: David Daney <ddaney.cavm@gmail.com>
To: "Kevin D. Kissell" <kevink@paralogos.com>
Cc: linux-mips@linux-mips.org
Subject: Re: Is r25 saved across syscalls?
Date: Mon, 10 Sep 2012 18:27:55 -0700 [thread overview]
Message-ID: <504E939B.5060209@gmail.com> (raw)
In-Reply-To: <504E8E27.5030904@paralogos.com>
On 09/10/2012 06:04 PM, Kevin D. Kissell wrote:
> On 09/10/2012 05:29 PM, Maciej W. Rozycki wrote:
>> I do wonder however why we have these instructions to save/restore $25
>> in SAVE_SOME/RESTORE_SOME. This dates back to 2.4 at the very least.
>> Ralf, any insights?
> Hi, guys. Maybe the fact that it's used for dispatching PIC calls has
> something to do with it?
>
I don't think so. It is call clobbered in all Linux ABIs. So there is
never a need to save it. It even has the pseudonym of $t9 indicating
that it will get clobbered.
The other call clobbered registers that happen to be saved are for the
nefarious uses of the kernel itself (a0..a6 for system call restarting),
I think this is just left over cruft.
David Daney
> /K.
>
>
>
>
next prev parent reply other threads:[~2012-09-11 1:28 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-09 19:30 Is r25 saved across syscalls? Rich Felker
2012-09-10 17:08 ` Ralf Baechle
2012-09-10 17:22 ` Rich Felker
2012-09-10 18:04 ` David Daney
2012-09-10 18:37 ` Rich Felker
2012-09-11 8:48 ` Ralf Baechle
2012-09-11 13:32 ` Rich Felker
2012-09-11 0:29 ` Maciej W. Rozycki
2012-09-11 1:04 ` Kevin D. Kissell
2012-09-11 1:27 ` David Daney [this message]
2012-09-11 2:28 ` Rich Felker
2012-09-11 8:58 ` Ralf Baechle
2012-09-11 8:12 ` Ralf Baechle
2012-09-11 13:44 ` Rich Felker
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