The cause details are below:
1. original C funtion:
JSValueEncodedAsPointer* JITStubs::cti_op_mod(STUB_ARGS)
{
BEGIN_STUB_FUNCTION(); //causes seg fault
JSValuePtr dividendValue = ARG_src1;
JSValuePtr divisorValue = ARG_src2;
CallFrame* callFrame = ARG_callFrame;
double d = dividendValue.toNumber(callFrame);
JSValuePtr result = jsNumber(ARG_globalData, fmod(d,
divisorValue.toNumber(callFrame)));
CHECK_FOR_EXCEPTION_AT_END();
return JSValuePtr::encode(result);
}
2. On X86:
Dump of assembler code for function _ZN3JSC8JITStubs10cti_op_modEPvz:
0x08141b12 <_ZN3JSC8JITStubs10cti_op_modEPvz+0>: push %ebp
0x08141b13 <_ZN3JSC8JITStubs10cti_op_modEPvz+1>: mov %esp,%ebp
0x08141b15 <_ZN3JSC8JITStubs10cti_op_modEPvz+3>: push %esi
0x08141b16 <_ZN3JSC8JITStubs10cti_op_modEPvz+4>: push %ebx
0x08141b17 <_ZN3JSC8JITStubs10cti_op_modEPvz+5>: sub $0x70,%esp
0x08141b1a <_ZN3JSC8JITStubs10cti_op_modEPvz+8>: call 0x80577bc
<__i686.get_pc_thunk.bx> //this system call is not exist in MIPS compiled code
0x08141b1f <_ZN3JSC8JITStubs10cti_op_modEPvz+13>: add $0xee049,%ebx
0x08141b25 <_ZN3JSC8JITStubs10cti_op_modEPvz+19>: lea 0xc(%ebp),%eax
//1677 BEGIN_STUB_FUNCTION();
0x08141b28 <_ZN3JSC8JITStubs10cti_op_modEPvz+22>: mov %eax,-0x1c(%ebp)
0x08141b2b <_ZN3JSC8JITStubs10cti_op_modEPvz+25>: mov -0x1c(%ebp),%eax
0x08141b2e <_ZN3JSC8JITStubs10cti_op_modEPvz+28>: sub $0x8,%eax
0x08141b31 <_ZN3JSC8JITStubs10cti_op_modEPvz+31>: mov %eax,0x4(%esp)
0x08141b35 <_ZN3JSC8JITStubs10cti_op_modEPvz+35>: lea -0x24(%ebp),%eax
0x08141b38 <_ZN3JSC8JITStubs10cti_op_modEPvz+38>: mov %eax,(%esp)
0x08141b3b <_ZN3JSC8JITStubs10cti_op_modEPvz+41>: call 0x8148e76
<StackHack> //242 ALWAYS_INLINE StackHack(void** location), MIPS
disasm has no symbols at all
3. On MIPS
Dump of assembler code for function _ZN3JSC8JITStubs10cti_op_modEPvz:
0x006abdb8 <_ZN3JSC8JITStubs10cti_op_modEPvz+0>: lui gp,0xf96
//this segment used on other routines and works
0x006abdbc <_ZN3JSC8JITStubs10cti_op_modEPvz+4>: addiu gp,gp,6776
0x006abdc0 <_ZN3JSC8JITStubs10cti_op_modEPvz+8>: addu gp,gp,t9
0x006abdc4 <_ZN3JSC8JITStubs10cti_op_modEPvz+12>: addiu sp,sp,-88
0x006abdc8 <_ZN3JSC8JITStubs10cti_op_modEPvz+16>: sw ra,80(sp)
0x006abdcc <_ZN3JSC8JITStubs10cti_op_modEPvz+20>: sw s8,76(sp)
0x006abdd0 <_ZN3JSC8JITStubs10cti_op_modEPvz+24>: sw s0,72(sp)
0x006abdd4 <_ZN3JSC8JITStubs10cti_op_modEPvz+28>: move s8,sp
0x006abdd8 <_ZN3JSC8JITStubs10cti_op_modEPvz+32>: sw gp,16(sp)
0x006abddc <_ZN3JSC8JITStubs10cti_op_modEPvz+36>: sw a1,92(s8)
0x006abde0 <_ZN3JSC8JITStubs10cti_op_modEPvz+40>: sw a2,96(s8)
0x006abde4 <_ZN3JSC8JITStubs10cti_op_modEPvz+44>: sw a3,100(s8)
0x006abde8 <_ZN3JSC8JITStubs10cti_op_modEPvz+48>: sw a0,88(s8)
0x006abdec <_ZN3JSC8JITStubs10cti_op_modEPvz+52>: addiu v0,s8,92
0x006abdf0 <_ZN3JSC8JITStubs10cti_op_modEPvz+56>: sw v0,24(s8)
0x006abdf4 <_ZN3JSC8JITStubs10cti_op_modEPvz+60>: addiu v1,s8,32
0x006abdf8 <_ZN3JSC8JITStubs10cti_op_modEPvz+64>: lw v0,24(s8)
0x006abdfc <_ZN3JSC8JITStubs10cti_op_modEPvz+68>: addiu v0,v0,-8
0x006abe00 <_ZN3JSC8JITStubs10cti_op_modEPvz+72>: move a0,v1
0x006abe04 <_ZN3JSC8JITStubs10cti_op_modEPvz+76>: move a1,v0
0x006abe08 <_ZN3JSC8JITStubs10cti_op_modEPvz+80>: lw t9,-19028(gp)
//seg fault here, -19028(gp) not accesible
0x006abe0c <_ZN3JSC8JITStubs10cti_op_modEPvz+84>: jalr t9
... no label in MIPS. <StackHack> label shown on X86 but on mips are all
xxx(gp), may be compiler/gdb not as good as X86 version?
thanks for look at it,
joe
--- On Wed, 4/22/09, x yz <last...@yahoo.com> wrote:
> From: x yz <last...@yahoo.com>
> Subject: Re: [webkit-dev] want to port JIT to MIPS - cti_op_mod(STUB_ARGS)
> seg fault
> To: "WebKit Development" <webkit-dev@lists.webkit.org>, "Gavin Barraclough"
> <barraclo...@apple.com>
> Date: Wednesday, April 22, 2009, 8:31 AM
> I use MIPS32EL, VA_LIST call, MIPS pushes function argument
> from left to right. I wrote a simple VA_LIST test it works
> on my box.
>
> BEGIN_STUB_FUNCTION() cause seg fault due to MIPS uses gp
> reg to read sth.
> I treied to rewrite the code like that:
> JSObject* JITStubs::cti_op_new_func_exp(STUB_ARGS)
> {
> va_list vl_args;
> va_start(vl_args, args);
> StackHack stackHack(&STUB_RETURN_ADDRESS_SLOT);
> JSValuePtr dividendValue = va_arg(vl_args, JSC::JSCell*
> );
> JSValuePtr divisorValue = va_arg(vl_args, JSC::JSCell*
> );
> ...
> }
>
> Still fail in stackHack(), if I comment out stackHack()
> then fails at va_arg.
>
> gp is a global register for common/public variables, the
> same usage before I call cti_op_mod() works fine.
>
> I also tried not use VA_LIST but REGISTER calling
> convention, still fail:
> (gdb) x/2i $at
> 0x6ab500
> <_ZN3JSC8JITStubs10cti_op_modEPPv>: lui gp,0xf96
> 0x6ab504
> <_ZN3JSC8JITStubs10cti_op_modEPPv+4>: addiu gp,gp,9008
> (gdb) x/20i $at
> 0x6ab500
> <_ZN3JSC8JITStubs10cti_op_modEPPv>: lui gp,0xf96
> 0x6ab504
> <_ZN3JSC8JITStubs10cti_op_modEPPv+4>: addiu gp,gp,9008
> 0x6ab508
> <_ZN3JSC8JITStubs10cti_op_modEPPv+8>: addu gp,gp,t9
> 0x6ab50c
> <_ZN3JSC8JITStubs10cti_op_modEPPv+12>: addiu sp,sp,-80
> 0x6ab510
> <_ZN3JSC8JITStubs10cti_op_modEPPv+16>: sw ra,72(sp)
> 0x6ab514
> <_ZN3JSC8JITStubs10cti_op_modEPPv+20>: sw s8,68(sp)
> 0x6ab518
> <_ZN3JSC8JITStubs10cti_op_modEPPv+24>: sw s0,64(sp)
> 0x6ab51c
> <_ZN3JSC8JITStubs10cti_op_modEPPv+28>: move s8,sp
> 0x6ab520
> <_ZN3JSC8JITStubs10cti_op_modEPPv+32>: sw gp,16(sp)
> 0x6ab524
> <_ZN3JSC8JITStubs10cti_op_modEPPv+36>: sw a0,80(s8)
> 0x6ab528
> <_ZN3JSC8JITStubs10cti_op_modEPPv+40>: lw v0,80(s8)
> 0x6ab52c
> <_ZN3JSC8JITStubs10cti_op_modEPPv+44>: addiu v0,v0,-4
> 0x6ab530
> <_ZN3JSC8JITStubs10cti_op_modEPPv+48>: addiu a0,s8,24
> 0x6ab534
> <_ZN3JSC8JITStubs10cti_op_modEPPv+52>: move a1,v0
> 0x6ab538
> <_ZN3JSC8JITStubs10cti_op_modEPPv+56>: lw t9,-19012(gp)
> 0x6ab53c
> <_ZN3JSC8JITStubs10cti_op_modEPPv+60>: jalr t9
> 0x6ab540 <_ZN3JSC8JITStubs10cti_op_modEPPv+64>: nop
> 0x6ab544
> <_ZN3JSC8JITStubs10cti_op_modEPPv+68>: lw gp,16(s8)
> 0x6ab548
> <_ZN3JSC8JITStubs10cti_op_modEPPv+72>: addiu v0,s8,32
> 0x6ab54c
> <_ZN3JSC8JITStubs10cti_op_modEPPv+76>: lw v1,80(s8)
> (gdb) stepi 14
>
> Program received signal SIGSEGV, Segmentation fault.
> 0x006ab538 in JSC::JITStubs::cti_op_mod (args=0x2aac9500)
> at
> /home/jdai/depot/mp/mediabase/head/libs/webkit-1.1.1/JavaScriptCore/jit/JITStubs.cpp:1685
> 1685 BEGIN_STUB_FUNCTION();
>
> another question is that there is no matched va_end() and
> it is a bug.
> thanks a lot for help,
> joe
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