Show current assembly instruction in GDB


Answers

You can do

display/i $pc

and every time GDB stops, it will display the disassembly of the next instruction.

GDB-7.0 also supports set disassemble-next-line on, which will disassemble the entire next line, and give you more of the disassembly context.

Question

I'm doing some assembly-level debugging in GDB. Is there a way to get GDB to show me the current assembly instruction in the same way that it shows the current source line? The default output after every command looks like this:

0x0001433f      990         Foo::bar(p);

This gives me the address of the current instruction, but I have to keep referring back to the output of disassemble in order to see which instruction I'm currently executing.




Setting the following option:

set  disassemble-next-line on
show disassemble-next-line

Will give you results that look like this:

(gdb) stepi
0x000002ce in ResetISR () at startup_gcc.c:245
245 {
   0x000002cc <ResetISR+0>: 80 b5   push    {r7, lr}
=> 0x000002ce <ResetISR+2>: 82 b0   sub sp, #8
   0x000002d0 <ResetISR+4>: 00 af   add r7, sp, #0
(gdb) stepi
0x000002d0  245 {
   0x000002cc <ResetISR+0>: 80 b5   push    {r7, lr}
   0x000002ce <ResetISR+2>: 82 b0   sub sp, #8
=> 0x000002d0 <ResetISR+4>: 00 af   add r7, sp, #0



From within gdb press Ctrl x 2 and the screen will split into 3 parts.

First part will show you the normal code in high level language.

Second will show you the assembly equivalent and corresponding instruction Pointer.

Third will present you the normal gdb prompt to enter commands.






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