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

On Fri, 2 Sep 2022 17:05:27 +0300 Konstantin Belousov
<kostikbel@gmail.com> wrote:
> On Fri, Sep 02, 2022 at 03:02:31PM +0200, Tijl Coosemans wrote:
>> 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"?  
> 
> You are right, please fix.

Fixed in cfdc649e455b.