GDB and opcodes

Question

Coming from a Windows environment, when I do kernel debugging or even in user mode for that matter, I can see the disassembled code in a way that is quite detailed, for example:

80526db2 6824020000      push    224h
80526db7 6808a14d80      push    offset nt!ObWatchHandles+0x8dc (804da108)
80526dbc e81f030100      call    nt!_SEH_prolog (805370e0)
80526dc1 a140a05480      mov     eax,dword ptr [nt!__security_cookie (8054a040)]

The first number is the address quite obviously but the second represent the opcode bytes and that is lacking on GDB or at least, I don't know how to get a similar result.

I usually will do something like this:

(gdb): display /i $pc

But all I get is something like this:

x/i $pc 0x21c4c: pop %eax

I can see what the code bytes are which is sometimes a bit of an issue for me. Is there something I can do with display that could help?

Edit: GDB in question is 6.3.50 on Mac OS X 10.8.3.

Answer 1

I think disassemble /r should give you what you are looking for:

(gdb) help disass
Disassemble a specified section of memory.
Default is the function surrounding the pc of the selected frame.
With a /m modifier, source lines are included (if available).
With a /r modifier, raw instructions in hex are included.
With a single argument, the function surrounding that address is dumped.
Two arguments (separated by a comma) are taken as a range of memory to dump,
  in the form of "start,end", or "start,+length".
(gdb) disass /r main
Dump of assembler code for function main:
   0x004004f8 <+0>:      55     push   %ebp
   0x004004f9 <+1>:      48     dec    %eax
   0x004004fa <+2>:      89 e5  mov    %esp,%ebp
   0x004004fc <+4>:      48     dec    %eax
   0x004004fd <+5>:      83 ec 10       sub    $0x10,%esp
   0x00400500 <+8>:      89 7d fc       mov    %edi,-0x4(%ebp)
   0x00400503 <+11>:     48     dec    %eax
   0x00400504 <+12>:     89 75 f0       mov    %esi,-0x10(%ebp)
   0x00400507 <+15>:     bf 0c 06 40 00 mov    $0x40060c,%edi
   0x0040050c <+20>:     b8 00 00 00 00 mov    $0x0,%eax
   0x00400511 <+25>:     e8 0a ff ff ff call   0x400420
   0x00400516 <+30>:     bf 00 00 00 00 mov    $0x0,%edi
   0x0040051b <+35>:     e8 10 ff ff ff call   0x400430
End of assembler dump.
(gdb) 

GDB disassemble command documentation

Answer 2

If you use lldb, you can use the -b option to disassemble to get the same effect:

(lldb) disassemble -b -p
Sketch`main + 46 at SKTMain.m:17:
-> 0x10001aa0e:  48 89 c7              movq   %rax, %rdi
   0x10001aa11:  b0 00                 movb   $0, %al
   0x10001aa13:  e8 f2 48 00 00        callq  0x10001f30a               ; symbol stub for: NSLog
   0x10001aa18:  48 8d 35 99 fa 00 00  leaq   64153(%rip), %rsi         ; @Sketch`.str3