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[V2,2/2] mips: remove register spill

Message ID 20201202033329.21759-3-huangpei@loongson.cn
State Changes Requested, archived
Headers
Series [V2,1/2] mips: add hp-timing support for MIPS R2 |

Commit Message

Huang Pei Dec. 2, 2020, 3:33 a.m. UTC 
  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

This also remove the unaligned stack pointer operation
---
 sysdeps/unix/sysv/linux/mips/mips64/syscall.S | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)

Comments

Adhemerval Zanella Netto Dec. 3, 2020, 12:39 p.m. UTC | #1 
On 02/12/2020 00:33, 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
> 
> This also remove the unaligned stack pointer operation

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  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 a9baff3c17..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, -SZREG
> +	.mask 0x00000000, 0
>  	.fmask 0x00000000, 0
> -	PTR_ADDIU sp, -SZREG
> -	cfi_adjust_cfa_offset (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, SZREG
> -	cfi_adjust_cfa_offset (-SZREG)
>  	bne a3, zero, L(error)
>  
>  	ret
>
Maciej W. Rozycki Dec. 4, 2020, 11:04 a.m. UTC | #2 
On Wed, 2 Dec 2020, 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.

 I object, as I previously noted.

  Maciej
diff mbox series

Patch

diff --git a/sysdeps/unix/sysv/linux/mips/mips64/syscall.S b/sysdeps/unix/sysv/linux/mips/mips64/syscall.S
index a9baff3c17..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, -SZREG
+	.mask 0x00000000, 0
 	.fmask 0x00000000, 0
-	PTR_ADDIU sp, -SZREG
-	cfi_adjust_cfa_offset (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, SZREG
-	cfi_adjust_cfa_offset (-SZREG)
 	bne a3, zero, L(error)
 
 	ret