gdbasm

Assembler plugin for gdb

What is it?

It is a script for gdb.

What does it do?

It lets you overwrite/modify assembly code in a location of choice.

How do I use it?

First, load it in gdb by using the command source. When debugging, you can use the command asm [address] to start assembling code at the specified address. If no address is given, then the current program counter is used. It will consume input until an empty line is found.

(gdb) source gdbasm.py
(gdb) x/3i $eip
=> 0x8048a37 <main+3>:  and    $0xfffffff0,%esp
   0x8048a3a <main+6>:  sub    $0x18bd0,%esp
   0x8048a40 <main+12>: mov    %gs:0x14,%eax
(gdb) asm
> nop
> xorl %eax, %eax
> nop
> 
(gdb) x/3i $eip
=> 0x8048a37 <main+3>:  nop
   0x8048a38 <main+4>:  xor    %eax,%eax
   0x8048a3a <main+6>:  nop
(gdb)

How does it work?

It calls as to assemble your code, and then overwrites the memory with the generated opcodes. If you want to use nasm, just modify AsmGen to generate an AssemblerNASM object instead of an AssemblerAS object.

What is its license?

BSD 3.

How can I make it auto-load?

Just add the following line to the file .gdbinit in your home folder.

source gdbasm.py