Re: [PATCH 2/2] alpha/ptrace: Add missing switch_stack frames

Al Viro
2021-06-16T20:29:03Z

On Wed, Jun 16, 2021 at 08:25:35PM +0000, Al Viro wrote:
> On Wed, Jun 16, 2021 at 01:32:50PM -0500, Eric W. Biederman wrote:
>
> > -.macro fork_like name
> > +.macro allregs name
> > .align 4
> > .globl alpha_\name
> > .ent alpha_\name
> > + .cfi_startproc
> > alpha_\name:
> > .prologue 0
> > - bsr $1, do_switch_stack
> > + SAVE_SWITCH_STACK
> > jsr $26, sys_\name
> > - ldq $26, 56($sp)
> > - lda $sp, SWITCH_STACK_SIZE($sp)
> > + RESTORE_SWITCH_STACK
>
> No. You've just added one hell of an overhead to fork(2),
> for no reason whatsoever. sys_fork() et.al. does *NOT* modify the
> callee-saved registers; it's plain C. So this change is complete
> BS.
>
> > +allregs exit
> > +allregs exit_group
>
> Details, please - what exactly makes exit(2) different from
> e.g. open(2)?

Ah... PTRACE_EVENT_EXIT garbage, fortunately having no counterparts in case of
open(2)... Still, WTF would you want to restore callee-saved registers for
in case of exit(2)?