Show current assembly instruction in GDB

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?

Answer 1

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

Answer 2

GDB Dashboard

https://github.com/cyrus-and/gdb-dashboard

This GDB configuration uses the official GDB Python API to show us whatever we want whenever GDB stops after for example next, much like TUI.

However I have found that this implementation is a more robust and configurable alternative to the built-in GDB TUI mode as explained at: gdb split view with code

For example, we can configure GDB Dashboard to show disassembly, source, registers and stack with:

dashboard -layout source assembly registers stack

Here is what it looks like if you enable all available views instead:

Related questions:

• Switching to assembly in gdb

Answer 3

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.

Answer 4

The command

x/i $pc

can be set to run all the time using the usual configuration mechanism.

Answer 5

You can switch to assembly layout in GDB:

(gdb) layout asm

See here for more information. The current assembly instruction will be shown in assembler window.

   ┌───────────────────────────────────────────────────────────────────────────┐
   │0x7ffff740d756 <__libc_start_main+214>  mov    0x39670b(%rip),%rax        #│
   │0x7ffff740d75d <__libc_start_main+221>  mov    0x8(%rsp),%rsi              │
   │0x7ffff740d762 <__libc_start_main+226>  mov    0x14(%rsp),%edi             │
   │0x7ffff740d766 <__libc_start_main+230>  mov    (%rax),%rdx                 │
   │0x7ffff740d769 <__libc_start_main+233>  callq  *0x18(%rsp)                 │
  >│0x7ffff740d76d <__libc_start_main+237>  mov    %eax,%edi                   │
   │0x7ffff740d76f <__libc_start_main+239>  callq  0x7ffff7427970 <exit>       │
   │0x7ffff740d774 <__libc_start_main+244>  xor    %edx,%edx                   │
   │0x7ffff740d776 <__libc_start_main+246>  jmpq   0x7ffff740d6b9 <__libc_start│
   │0x7ffff740d77b <__libc_start_main+251>  mov    0x39ca2e(%rip),%rax        #│
   │0x7ffff740d782 <__libc_start_main+258>  ror    $0x11,%rax                  │
   │0x7ffff740d786 <__libc_start_main+262>  xor    %fs:0x30,%rax               │
   │0x7ffff740d78f <__libc_start_main+271>  callq  *%rax                       │
   └───────────────────────────────────────────────────────────────────────────┘
multi-thre process 3718 In: __libc_start_main     Line: ??   PC: 0x7ffff740d76d
#3  0x00007ffff7466eb5 in _IO_do_write () from /lib/x86_64-linux-gnu/libc.so.6
#4  0x00007ffff74671ff in _IO_file_overflow ()
   from /lib/x86_64-linux-gnu/libc.so.6
#5  0x0000000000408756 in ?? ()
#6  0x0000000000403980 in ?? ()
#7  0x00007ffff740d76d in __libc_start_main ()
   from /lib/x86_64-linux-gnu/libc.so.6
(gdb)

Answer 6

There is a simple solution that consists in using stepi, which in turns moves forward by 1 asm instruction and shows the surrounding asm code.