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

[Lai Jiangshan]

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.

The code doing the stash in userspace may be in
arch/x86/entry/vdso/vdso32/system_call.S (see SYSCALL_SEQUENCE)

Thanks
Lai