[PATCH 3/3] mips: remove register spill

[Huang Pei]

hi,

On Mon, Nov 30, 2020 at 11:22:03AM -0300, Adhemerval Zanella wrote:
> 
> 
> On 28/11/2020 05:18, Huang Pei wrote:
> > Before Linux/MIPS 2.6.36, kernel expected setting syscall number(aka
> > "li v0, #sys_number") right precedes "syscall", so the kernel syscall
> > restart sequence can use CP0 EPC - 4 to restart the syscall, because
> > kernel DID NOT save v0 during syscall handling. Linux 2.6.36 canceled
> > this restriction.
> > 
> > See sysdeps/unix/sysv/linux/mips/{mips32/sysdep.h,mips64/sysdep.h,sysdep.h}
> > 
> > Since glibc-2.24 the minimum kernel version is 3.2(much higer than
> > 2.6.36), I think it is OK to remove the ugly register spill in
> > syscall.S just because of the old convention
> > 
> > Signed-off-by: Huang Pei <huangpei@loongson.cn>
> 
> We do not use SCO, but rather Copyright assignment.	
> 
> The rest of the patch looks ok.
> 

I would like to combine the Patch 2/3 and Patch 3/3 into one patch,
since Patch 2/3 only fix sp alignment, but the key point is folllowing syscall
restart convention, any advice?

> > ---
> >  sysdeps/unix/sysv/linux/mips/mips64/syscall.S | 14 ++------------
> >  1 file changed, 2 insertions(+), 12 deletions(-)
> > 
> > diff --git a/sysdeps/unix/sysv/linux/mips/mips64/syscall.S b/sysdeps/unix/sysv/linux/mips/mips64/syscall.S
> > index aab1f389aa..089524a40b 100644
> > --- a/sysdeps/unix/sysv/linux/mips/mips64/syscall.S
> > +++ b/sysdeps/unix/sysv/linux/mips/mips64/syscall.S
> > @@ -27,14 +27,9 @@
> >  
> >  	.text
> >  NESTED (syscall, SZREG, ra)
> > -	.mask 0x00010000, -2 * SZREG
> > +	.mask 0x00000000, 0
> >  	.fmask 0x00000000, 0
> > -	PTR_ADDIU sp, -2 * SZREG
> > -	cfi_adjust_cfa_offset (2 * SZREG)
> > -	REG_S s0, (sp)
> > -	cfi_rel_offset (s0, 0)
> > -
> > -	move s0, a0
> > +	move v0, a0
> >  	move a0, a1		/* shift arg1 - arg7.  */
> >  	move a1, a2
> >  	move a2, a3
> > @@ -43,13 +38,8 @@ NESTED (syscall, SZREG, ra)
> >  	move a5, a6
> >  	move a6, a7
> >  
> > -	move v0, s0		/* Syscall number -> v0 */
> >  	syscall			/* Do the system call.  */
> >  
> > -	REG_L s0, (sp)
> > -	cfi_restore (s0)
> > -	PTR_ADDIU sp, 2 * SZREG
> > -	cfi_adjust_cfa_offset (-2 * 2 * SZREG)
> >  	bne a3, zero, L(error)
> >  
> >  	ret
> >