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

[Al Viro]

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)?