6 Jan
2018
6 Jan
'18
2:57 a.m.
On Fri, Jan 05, 2018 at 03:33:55PM -0800, Vineet Gupta wrote:
On 12/13/2017 10:29 PM, Stafford Horne wrote:
Hello Vineet,
Thanks for testing, I did realize varargs might generate slightly less optimal
code. But I figured a few thing things
- syscall() is probably not going to be used in any critical code sections.
- the compiler could be optimized to make the varargs handling more optimal
- we could remove code (but actually ends up with a bigger binary, so not
great)
But for now, lets just drop this patch. Thanks for the feedback.
-Stafford
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(a)gmail.com>
---
libc/sysdeps/linux/arc/Makefile.arch | 2 +-
libc/sysdeps/linux/arc/syscall.c | 17 -----------------
2 files changed, 1 insertion(+), 18 deletions(-)
[snip]
-
-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