Re: git: e8b2980e4a12 - main - i386 doreti: stop saving/restoring %ecx around calls into C

On Wed, 24 Aug 2022 19:25:12 GMT Konstantin Belousov <kib@FreeBSD.org>
wrote:
> The branch main has been updated by kib:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=e8b2980e4a126407e15d33ee8d987385c8321261
> 
> commit e8b2980e4a126407e15d33ee8d987385c8321261
> Author:     Konstantin Belousov <kib@FreeBSD.org>
> AuthorDate: 2022-08-18 04:07:29 +0000
> Commit:     Konstantin Belousov <kib@FreeBSD.org>
> CommitDate: 2022-08-24 19:12:05 +0000
> 
>     i386 doreti: stop saving/restoring %ecx around calls into C
>     
>     There is no reason to do this.  Instead just calculate it later.
>     
>     Reviewed by:    jhb
>     Tested by:      pho
>     Sponsored by:   The FreeBSD Foundation
>     MFC after:      1 week
>     Differential revision:  https://reviews.freebsd.org/D36302
> ---
>  sys/i386/i386/exception.s | 17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/sys/i386/i386/exception.s b/sys/i386/i386/exception.s
> index 5eef9c1d512c..8279a4602ebf 100644
> --- a/sys/i386/i386/exception.s
> +++ b/sys/i386/i386/exception.s
> @@ -518,22 +518,21 @@ doreti_exit:
>  	je	doreti_iret_nmi
>  	cmpl	$T_TRCTRAP, TF_TRAPNO(%esp)
>  	je	doreti_iret_nmi
> -	movl	$TF_SZ, %ecx
>  	testl	$PSL_VM,TF_EFLAGS(%esp)
> -	jz	1f			/* PCB_VM86CALL is not set */
> -	addl	$VM86_STACK_SPACE, %ecx
> -	jmp	2f
> -1:	testl	$SEL_RPL_MASK, TF_CS(%esp)
> +	jnz	1f			/* PCB_VM86CALL is not set */
> +	testl	$SEL_RPL_MASK, TF_CS(%esp)
>  	jz	doreti_popl_fs
> -2:	movl	$handle_ibrs_exit,%eax
> -	pushl	%ecx			/* preserve enough call-used regs */
> +1:	movl	$handle_ibrs_exit,%eax
>  	call	*%eax
>  	movl	mds_handler,%eax
>  	call	*%eax
> -	popl	%ecx
>  	movl	%esp, %esi
>  	movl	PCPU(TRAMPSTK), %edx
> -	subl	%ecx, %edx
> +	movl	$TF_SZ, %ecx
> +	testl	$PSL_VM,TF_EFLAGS(%esp)
> +	jz	2f			/* PCB_VM86CALL is not set */
> +	addl	$VM86_STACK_SPACE, %ecx
> +2:	subl	$TF_SZ, %edx

Shouldn't this be "subl %ecx, %edx"?