Segfault with JIT

Hi all,

I've noticed that on this system (Athlon 1ghz, Debian unstable, gcc3) 
certain example assembly programs, specfically: call, euclid, fact, 
life, mops_p, queens, stack and substr all segfault.

Here is what I was able to find out, for the "substr" program, the 
following is part of the disassembly of the JIT-ized code, according to GDB:

0x80edc88:      push   %ebp
0x80edc89:      mov    %esp,%ebp
0x80edc8b:      movl   $0x1,0x80dc018
0x80edc95:      movl   $0x0,0x80dc014
0x80edc9f:      mov    0xbffff5d0,%eax
0x80edca4:      mov    %eax,0x80db720
0x80edca9:      push   $0x80ed930
0x80edcae:      pushl  0x80db720
0x80edcb4:      call   0x8057a60 <string_copy>
0x80edcb9:      mov    %eax,0x80e2014
0x80edcbe:      movl   $0x0,0x80dc01c
0x80edcc8:      movl   $0x0,0x80dc020
0x80edcd2:      add    %al,(%eax)
0x80edcd4:      movl   $0x1,0x80db724
0x80edcde:      mov    0x80e2018,%eax
0x80edce3:      mov    (%eax),%eax
0x80edce5:      mov    %eax,0x80db720
0x80edcea:      mov    0x80e2018,%eax

Notice the instructions:

0x80edcde:      mov    0x80e2018,%eax
0x80edce3:      mov    (%eax),%eax

This is where it dies, 0x80e2018 contains a zero, and (%eax) attempts to 
access it, segfault.

Unfortunately I'm not 3l33t enough to read hex yet, maybe I'll write a 
little assembler for the .jit files? Or at least some sort of 
disassembly display tool :)

print "Merry $your_holiday\n"

-- 
Rafael Kitover

• Segfault with JIT by Rafael Kitover
• Re: Segfault with JIT by Daniel Grunblatt
• Re: Segfault with JIT by Daniel Grunblatt