Mac Intel

Joel Reymont <>
Mon Aug 14 04:17:01 CEST 2006

One last thing...

The 0xdd opcode corresponds to fstpl (0xddd8). The FPU IP seems to be  
pointing to fstpl below, in the dump of do_fmul. I don't understand,  
though, why mc->fs.fpu_mxcsr & 0x000F is true since fstpl is not a  
SSE2 instruction.

I'm gonna revisit this tomorrow but so far I see that 1) the test  
program is looping, repeatedly firing exceptions, 2) MXCSR has bits  
in it set, 3) the IP is not a SSE2 instruction and 4) I clear the FPU  
state with *((unsigned short *)&mc->fs.fpu_fsw) &= ~0xFF; before  
exiting the SIGFPE handler.


void do_fmul(void)
     res = atof(a) * atof(b);

Dump of assembler code for function do_fmul:
0x00001d6d <do_fmul+0>: push   %ebp
0x00001d6e <do_fmul+1>: mov    %esp,%ebp
0x00001d70 <do_fmul+3>: push   %ebx
0x00001d71 <do_fmul+4>: sub    $0x24,%esp
0x00001d74 <do_fmul+7>: call   0x1ffc <__i686.get_pc_thunk.bx>
0x00001d79 <do_fmul+12>:        lea    663(%ebx),%eax
0x00001d7f <do_fmul+18>:        mov    (%eax),%eax
0x00001d81 <do_fmul+20>:        mov    %eax,(%esp)
0x00001d84 <do_fmul+23>:        call   0x302c <dyld_stub_atof>
0x00001d89 <do_fmul+28>:        fstpl  -24(%ebp)
0x00001d8c <do_fmul+31>:        lea    667(%ebx),%eax
0x00001d92 <do_fmul+37>:        mov    (%eax),%eax
0x00001d94 <do_fmul+39>:        mov    %eax,(%esp)
0x00001d97 <do_fmul+42>:        call   0x302c <dyld_stub_atof>
0x00001d9c <do_fmul+47>:        fstpl  -16(%ebp)
0x00001d9f <do_fmul+50>:        movsd  -24(%ebp),%xmm0
0x00001da4 <do_fmul+55>:        mulsd  -16(%ebp),%xmm0
0x00001da9 <do_fmul+60>:        lea    4755(%ebx),%eax
0x00001daf <do_fmul+66>:        mov    (%eax),%eax
0x00001db1 <do_fmul+68>:        movsd  %xmm0,(%eax)
0x00001db5 <do_fmul+72>:        add    $0x24,%esp
0x00001db8 <do_fmul+75>:        pop    %ebx
0x00001db9 <do_fmul+76>:        pop    %ebp
0x00001dba <do_fmul+77>:        ret
End of assembler dump.


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