better assembly level debugging

Francois
2011-05-02T15:34:55Z

Hello

I'm trying to do some machine code-level debugging using GDB.
Basically, I'm debugging a C application that provides no debugging
symbol.

GDB works greatly, and I think a few customization could make it as
nice as the other popular debugging alternatives for this task (like
OllyDbg for Win32).

- defining labels
reverse engineering is very difficult without debugging symbols. It
would be very handy if I could (like on IDA or OllyDbg) define my own
labels. That would be for example user-defined symbols, which could be
used to get a nicer output.
For example
set label 0x402000 log_error
would define a new symbol "log_error". Further disassembly of "call
0x402000" instruction, or stepping near this address would give a
cleaner output.

- pretty printer for instructions
GDB could pretty print what it disassembles so that values of operands
are introspected (looking for strings or functions especially)

Let's take an example :

#include <stdio.h>
#include <wchar.h>
int main() {
int (*printIt) (const wchar_t*, ...) = wprintf;
const wchar_t* foo = L"foo 42";
printIt(foo);
}

compiled with g++ -o wide wide.cpp, I see:
=> 0x0000000000400690 <+4>: sub $0x10,%rsp
0x0000000000400694 <+8>: movq $0x400578,-0x10(%rbp)
0x000000000040069c <+16>: movq $0x4007ac,-0x8(%rbp)
...

which contains zero indication for reading.
I would expect
0x400578 to be commented as # <wprintf@plt> and
0x4007ac to be commented as # L"foo 42"

moreover, if compiled with g++ -o wide wide.cpp -fPIC, the first lines
above change to
=> 0x400680 <main+4>: sub $0x10,%rsp
0x400684 <main+8>: mov 0x1003fd(%rip),%rax # 0x500a88
0x40068b <main+15>: mov %rax,-0x10(%rbp)
0x40068f <main+19>: lea 0x106(%rip),%rax # 0x40079c

once again, we need to run
x/a 0x500a88
x/ws 0x40079c
to get an understandable disassembly.

Do you think these features could be integrated in GDB? If yes I could
send some code for review.

Francois