I'm working on a binary translator that translates MIPS binaries into Java
bytecode (http://spel.bth.se/index.php/Cibyl) with the goal of "recompiling" C
programs to run on J2ME. To simplify things, I use compile programs for a
subset of the MIPS1 instruction set, and ideally I would like to get rid of
delayed instructions.
So, I used the -fno-delayed-branch instruction when compiling. The GCC version
is
mips-linux-gcc (GCC) 3.4.4 20050314 (prerelease) (Debian 3.4.3-13)
(an emdebian.org binary), and the command line i used is
mips-linux-gcc -Wall -mips1 -fno-delayed-branch -O2 -fno-pic -mno-abicalls
-I/home/ska/projects/private/games/mophun/cibyl/trunk//include -O2 -c main.c
-o main.o
For the code below,
#define _syscall1(type,name,atype,a) \
type name(atype a) \
{ \
register unsigned long __a0 asm("$4") = (unsigned long) a; \
register unsigned long __v0 asm("$2"); \
\
__asm__ volatile ( \
".set\tnoreorder\n\t" \
"li\t$2, %2\t\t\t# " #name "\n\t" \
"syscall\n\t" \
".set\treorder" \
: "=&r" (__v0) \
: "r" (__a0), "i" (__NR_##name) \
); \
\
return (type) __v0; \
}
#define __NR_exit 0
static inline _syscall1(void,exit , int, code );
int tst(int *argv)
{
int x;
for (x = 0; x < 24; x++)
exit(argv[x]);
return 0;
}
I get instructions in the delay slots of bgez and jr:
00000000 <tst>:
0: 00801821 move v1,a0
4: 24050017 li a1,23
8: 8c640000 lw a0,0(v1)
c: 24020000 li v0,0
10: 0000000c syscall
14: 24a5ffff addiu a1,a1,-1
18: 04a1fffb bgez a1,8 <tst+0x8>
1c: 24630004 addiu v1,v1,4
20: 03e00008 jr ra
24: 00001021 move v0,zero
...
Which is not what I had expected. If i replace the "syscall" exit with a
function call instead, I get the expected behavior:
00000000 <exit3>:
0: 08000000 j 0 <exit3>
4: 00000000 nop
00000008 <tst>:
8: 27bdffe0 addiu sp,sp,-32
c: afb10014 sw s1,20(sp)
10: afb00010 sw s0,16(sp)
14: afbf0018 sw ra,24(sp)
18: 00808021 move s0,a0
1c: 24110017 li s1,23
20: 8e040000 lw a0,0(s0)
24: 2631ffff addiu s1,s1,-1
28: 0c000000 jal 0 <exit3>
2c: 00000000 nop
30: 26100004 addiu s0,s0,4
34: 0621fffa bgez s1,20 <tst+0x18>
38: 00000000 nop
3c: 8fbf0018 lw ra,24(sp)
40: 8fb10014 lw s1,20(sp)
44: 8fb00010 lw s0,16(sp)
48: 00001021 move v0,zero
4c: 27bd0020 addiu sp,sp,32
50: 03e00008 jr ra
54: 00000000 nop
...
--
Summary: -fno-delayed-branch does not seem to work with the MIPS
branch instructions
Product: gcc
Version: 3.4.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: ska at bth dot se
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28325
