Re: [PATCH 3/6] x86/entry: Use PUSH_AND_CLEAR_REGS for compat

[Guenter Roeck]

On 5/19/22 18:11, Lai Jiangshan wrote:
> On Fri, May 20, 2022 at 1:35 AM Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:
> > diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
> > index ed2be3615b50..f76e674d22c4 100644
> > --- a/arch/x86/entry/entry_64_compat.S
> > +++ b/arch/x86/entry/entry_64_compat.S
> > @@ -200,7 +200,7 @@ SYM_INNER_LABEL(entry_SYSCALL_compat_safe_stack, SYM_L_GLOBAL)
> >   SYM_INNER_LABEL(entry_SYSCALL_compat_after_hwframe, SYM_L_GLOBAL)
> >          movl    %eax, %eax              /* discard orig_ax high bits */
> >          pushq   %rax                    /* pt_regs->orig_ax */
> > -       PUSH_AND_CLEAR_REGS rax=$-ENOSYS
> > +       PUSH_AND_CLEAR_REGS rcx=%rbp rax=$-ENOSYS
>
> Some comments need to be here to explain why %rcx is stashed in %rbp.

I am curious. That comment wasn't needed before the problem fixed here
was introduced. The comment is unrelated to the bug fix. Why is it needed
now, and why would it be a prerequisite for fixing a critical bug ?
Shouldn't that comment be added in a separate patch ?

Thanks,
Guenter