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
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