[uclibc-ng-devel] [PATCH 4/4] arc: Use new common syscall() implementation

Vineet Gupta Vineet.Gupta1 at synopsys.com
Sat Jan 6 00:33:55 CET 2018

On 12/13/2017 10:29 PM, Stafford Horne wrote:
> Traditionally arc has had a generic syscall implementation of syscall()
> matchig the common implementation.
> During an audit it was found that this implementation seems to duplicate
> common implementation and is no longer needed.
> Signed-off-by: Stafford Horne <shorne at gmail.com>
> ---
>   libc/sysdeps/linux/arc/Makefile.arch |  2 +-
>   libc/sysdeps/linux/arc/syscall.c     | 17 -----------------
>   2 files changed, 1 insertion(+), 18 deletions(-)

> -extern long syscall(long int sysnum, long a, long b, long c, long d, long e, long f);
> -
> -long syscall(long int sysnum, long a, long b, long c, long d, long e, long f)
> -{
> -	return INLINE_SYSCALL_NCS(sysnum, 6, a, b, c, d, e, f);
> -}

varargs generate pathetic code on ARC atleast, it is partly due to the ABI (the 
args need to be stored on stack)

With current implementation we get

000100ac <syscall>:
    100ac:	mov_s	r8,r0
    100ae:	mov_s	r0,r1
    100b0:	mov_s	r1,r2
    100b2:	mov_s	r2,r3
    100b4:	mov_s	r3,r4
    100b6:	mov_s	r4,r5
    100b8:	mov_s	r5,r6
    100ba:	trap_s	0
    100bc:	cmp	r0,-1024
    100c0:	jls	[blink]
    100c4:	st.aw	blink,[sp,-4]
    100c8:	bl	84	;1011c <__syscall_error>
    100cc:	ld.ab	blink,[sp,4]
    100d0:	j_s	[blink]
    100d2:	nop_s

With varagrs implementation we get tons of useless stores. So I'd prefer we keep 
the current implementation for ARC - although granted syscall() may not be the 
fast path syscall.

00010398 <syscall>:
    10398:	sub_s	sp,sp,0x1c
    1039a:	mov_s	r8,r0
    1039c:	st_s	r1,[sp,0]
    1039e:	st_s	r2,[sp,0x4]
    103a0:	st_s	r3,[sp,0x8]
    103a2:	st	r4,[sp,12]
    103a6:	st	r5,[sp,16]
    103aa:	st	r6,[sp,20]
    103ae:	st	r7,[sp,24]
    103b2:	mov_s	r0,r1
    103b4:	mov_s	r1,r2
    103b6:	mov_s	r2,r3
    103b8:	mov_s	r3,r4
    103ba:	mov_s	r4,r5
    103bc:	mov_s	r5,r6
    103be:	trap_s	0
    103c0:	brhs.nt	0xfffffc00,r0,20	;103d4 <syscall+0x3c>
    103c8:	st.aw	blink,[sp,-4]
    103cc:	bl	84	;10420 <__syscall_error>
    103d0:	ld.ab	blink,[sp,4]
    103d4:	j_s.d	[blink]
    103d6:	add_s	sp,sp,0x1c

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