Archive for the ‘Sticker’ Category

Feeling too lazy!

December 27th, 2005

Sticker needs a bit of design change & i’m feeling too lazy to do that!

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Get up makuchaku!

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Child notifies parent before terminating…

December 26th, 2005

Finally managed to get hold of SIGCHLD signal when the child terminates.
The code can be found here.

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Non-blocking wait…

December 24th, 2005

The parent wants to wait() for child’s exit, but not blockingly… how to do this?

One of the solution, i found was to trap SIGCHILD. This signal is sent to the parent on child’s termination. The parent can then loop on a bolean variable to check for child’s existance, while doing other work… something i needed exactly for sticker!

Lets see, will it work as i wanted or not… :-)

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PTRACE_SINGLESTEP

December 22nd, 2005

ptrace() needs to be reminded again & again that in what mode is it operating. So if you have to single-step through all the instructions in a program, you need to constantly call (or set) ptrace request to PTRACE_SINGLESTEP

For example, this code will just single-step through first 10 instructions.

while(1)
{
 wait(&status);
 if(WIFEXITED(status))
 {
  printf("Breaking\n");
  break;
 }

 ptrace(PTRACE_GETREGS, child, NULL, &regs);
 ins = ptrace(PTRACE_PEEKTEXT, child, regs.eip, NULL);
 printf("(i = %d) EIP : 0x%X (%X)\n", i, regs.eip, ins);
 i++;

 if(i < 10 )
 ptrace(PTRACE_SINGLESTEP, child, NULL, NULL);
}

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Disassembling Hello World…

December 22nd, 2005

(gdb) disassemble main
Dump of assembler code for function main:
0×08048368 : push %ebp
0×08048369 : mov %esp,%ebp
0×0804836b : sub $0×8,%esp
0×0804836e : and $0xfffffff0,%esp
0×08048371 : mov $0×0,%eax
0×08048376 : add $0xf,%eax
0×08048379 : add $0xf,%eax
0×0804837c : shr $0×4,%eax
0×0804837f : shl $0×4,%eax
0×08048382 : sub %eax,%esp
0×08048384 : sub $0xc,%esp
0×08048387 : push $0×804847c
0×0804838c : call 0×80482b0 <_init+56>
0×08048391 : add $0×10,%esp
0×08048394 : mov $0×0,%eax
0×08048399 : leave
0×0804839a : ret
End of assembler dump.

(gdb) x/51xb 0×08048368
0×8048368

: 0×55 0×89 0xe5 0×83 0xec 0×08 0×83 0xe4
0×8048370 : 0xf0 0xb8 0×00 0×00 0×00 0×00 0×83 0xc0
0×8048378 : 0×0f 0×83 0xc0 0×0f 0xc1 0xe8 0×04 0xc1
0×8048380 : 0xe0 0×04 0×29 0xc4 0×83 0xec 0×0c 0×68
0×8048388 : 0×7c 0×84 0×04 0×08 0xe8 0×1f 0xff 0xff
0×8048390 : 0xff 0×83 0xc4 0×10 0xb8 0×00 0×00 0×00
0×8048398 : 0×00 0xc9 0xc3

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