Re: Is r25 saved across syscalls?

[David Daney <ddaney.cavm@gmail.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.