for a function like this:
int i(int b)
{

        int i1,i2,i3;
        return i1 + i2;

}

in x86, compile with gcc -fno-pic -fomit-frame-pointer -gstabs -O0 -S the output is:
Lscope1:
.stabs "i:F(0,1)",36,0,0,i
.stabs "b:p(0,1)",160,0,0,-20
.globl i
.type i, @function
i:
.stabn 68,0,10,.LM5-.LFBB2
.LM5:
.LFBB2:
.LFB1:
.cfi_startproc
movl %edi, -20(%rsp)
.stabn 68,0,12,.LM6-.LFBB2
.LM6:
movl -8(%rsp), %eax
movl -4(%rsp), %edx
leal (%rdx,%rax), %eax
.stabn 68,0,13,.LM7-.LFBB2
.LM7:
ret
.cfi_endproc
.LFE1:
.size i, .-i
.stabs "i1:(0,1)",128,0,0,-4
.stabs "i2:(0,1)",128,0,0,-8
.stabs "i3:(0,1)",128,0,0,-12
.stabn 192,0,0,.LFBB2-.LFBB2
.stabn 224,0,0,.Lscope2-.LFBB2

Everything works as expect:
the offsets for both parameters and locals are negative, no matter in stabs directive or in the assembly code. And the offset value in stabs equals to the one in the code.

But for mips, mipsel-linux-gcc -fno-pic -fomit-frame-pointer -gstabs -O0 -S output is:
scope1:
.align 2
.stabs "i:F(0,1)",36,0,0,i
.stabs "b:p(0,1)",160,0,0,24
.globl i
.ent i
.type i, @function
i:
.stabn 68,0,10,$LM5
$LM5:
$LFBB2:
.set nomips16
.frame $sp,24,$31 # vars= 16, regs= 0/0, args= 0, gp= 8 .mask 0x00000000,0
.fmask 0x00000000,0
.set noreorder
.set nomacro

addiu $sp,$sp,-24
.cprestore 0
sw $4,24($sp)
.stabn 68,0,12,$LM6
$LM6:
lw $3,16($sp)
lw $2,12($sp)
nop
addu $2,$3,$2
.stabn 68,0,13,$LM7
$LM7:
addiu $sp,$sp,24
j $31
nop

.set macro
.set reorder
.end i
.stabs "i1:(0,1)",128,0,0,-8
.stabs "i2:(0,1)",128,0,0,-12

The local variable offsets in stabs are negative, but in the code they are positive. For my understanding of fpc logic, they should both generated from loc.reference.offset or something similiar, they cannot be different. If I am not making mistake, we have to special case some code to make debugging work.

Am I wrong?

Regards

After looking into the gcc code, it is really so uncommon:( Lots of pain to get full support.

gcc-4.4.6/gcc/config/mips/mips.c
line 7484:
/* The MIPS debug format wants all automatic variables and arguments to be in terms of the virtual frame pointer (stack pointer before any adjustment in the function), while the MIPS 3.0 linker wants the frame pointer to be the stack pointer after the initial adjustment. So, we do the adjustment here. The arg pointer (which is eliminated) points to the virtual frame pointer, while the frame pointer (which may be eliminated) points to the stack pointer after the initial adjustments. */

HOST_WIDE_INT
mips_debugger_offset (rtx addr, HOST_WIDE_INT offset) {

  rtx offset2 = const0_rtx;
  rtx reg = eliminate_constant_term (addr, &offset2);

  if (offset == 0)
    offset = INTVAL (offset2);
  if (reg == stack_pointer_rtx
      || reg == frame_pointer_rtx
      || reg == hard_frame_pointer_rtx)
    {
      offset -= cfun->machine->frame.total_size; // here it is
      if (reg == hard_frame_pointer_rtx)
        offset += cfun->machine->frame.hard_frame_pointer_offset;
    }