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

[Eric W. Biederman]

Al Viro <viro@xxxxxxxxxxxxxxxxxx> writes:

> 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.

Fork already saves the registers, all I did was restore them.  Which
makes a debugger that modifies them in
PTRACE_EVENT_{FORK,VFORK,CLONE,VFORK_DONE} work.

>> +allregs exit
>> +allregs exit_group
>
> 	Details, please - what exactly makes exit(2) different from
> e.g. open(2)?

PTRACE_EVENT_EXIT.


Eric