Debugging Binaries

Our binaries are static, and have no debug information, so it might be a challenge to debug them

GDB

Load the binary into GDB:

 $ gdb a.out
 Reading symbols from a.out...
 (No debugging symbols found in a.out)
 (gdb)

Start the binary, via "starti":

(gdb) starti
Starting program: /home/skx/s-lang/a.out

Program stopped.
0x0000000000401013 in ?? ()

You can now enter stepi to step forward, and keep pressing RETURN to repeat the command. Or run stepi 100 to step forward 100 instructions.

At any time you may show register contents via info registers or info registers float.

You might try the new GDB TUI options:

• layout asm
  • Show the disassembly at the point.
• layout regs
  • Show the register, and flag contents.

Tracing

You can use the included trace.gdb file to automate single-stepping and logging execution.

Launch GDB with a binary and the script like so:

gdb  a.out -x trace.gdb

Then your output will be saved into the file trace.log. You can update the trace-script to log registers, but that gets quite noisy.

Handy Tips

If you start tracing into a function you can enter finish to continue execution until the function returns.

Instead of running stepi you can enter nexti to skip over a call.

Disassembly

I always prefer set disassembly-flavor intel because I'm old-school.

You can make that the default via:

echo "set disassembly-flavor intel" >> ~/.gdbinit