From: Ralf Baechle <ralf@linux-mips.org>
To: "Maciej W. Rozycki" <macro@linux-mips.org>
Cc: Rich Felker <dalias@aerifal.cx>, linux-mips@linux-mips.org
Subject: Re: Is r25 saved across syscalls?
Date: Tue, 11 Sep 2012 10:58:27 +0200 [thread overview]
Message-ID: <20120911085827.GF24448@linux-mips.org> (raw)
In-Reply-To: <alpine.LFD.2.00.1209110059580.8926@eddie.linux-mips.org>
On Tue, Sep 11, 2012 at 01:29:52AM +0100, Maciej W. Rozycki wrote:
> Relying on any call-clobbered registers, including $7 to be preserved
> across a syscall is risky, to say the least, as this is not guaranteed by
> the syscall ABI. 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?
It dates back to the initial commit in 36ea5120 from March 27, 1998 for
2.1.90 when for the sake of better lmbench syscall latency numbers I had
introduced the concept of partial saving of a register frame. I think it
should rather have been in SAVE_TEMP/RESTORE_TEMP instead.
Ralf
next prev parent reply other threads:[~2012-09-11 8:58 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
2012-09-11 2:28 ` Rich Felker
2012-09-11 8:58 ` Ralf Baechle [this message]
2012-09-11 8:12 ` Ralf Baechle
2012-09-11 13:44 ` Rich Felker
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