GCC/objdump: Generating compilable/buildable assembly (interspersed with C/C++) source?

Question

This is close to Using GCC to produce readable assembly?, but my context here is avr-gcc (and correspondingly, avr-objdump) for Atmel (though, I guess it would apply across the GCC board).

The thing is, I have a project of multiple .c and .cpp files; which ultimately get compiled into an executable, with the same name as the 'master' .cpp file. In this process, I can obtain assembly listing in two ways:

I can instruct gcc to emit assembly listing source (see Linux Assembly and Disassembly an Introduction) using the -S switch; in this case, I get a file, with contents like:

...
loop:
  push r14
  push r15
  push r16
  push r17
  push r28
  push r29
/* prologue: function /
/ frame size = 0 */
  ldi r24,lo8(13)
  ldi r22,lo8(1)
  call digitalWrite
  rjmp .L2
.L3:
  ldi r24,lo8(MyObj)
  ldi r25,hi8(MyObj)
  call _ZN16MYOBJ7connectEv
.L2:
  ldi r24,lo8(MyObj)
  ldi r25,hi8(MyObj)
  call _ZN16MYOBJ11isConnectedEv
...

(Haven't tried it yet; but I guess this code is compilable/buildable....)

I can inspect the final executable with, and instruct, objdump to emit assembly listing source using the -S switch; in this case, I get a file, with contents like:

...
0000066a <init>:
void init()
{
        // this needs to be called before setup() or some functions won't
        // work there
        sei();
     66a:       78 94           sei
     66c:       83 b7           in      r24, 0x33       ; 51
     66e:       84 60           ori     r24, 0x04       ; 4
     670:       83 bf           out     0x33, r24       ; 51
...
000006be <loop>:
     6be:       ef 92           push    r14
     6c0:       ff 92           push    r15
     6c2:       0f 93           push    r16
     6c4:       1f 93           push    r17
     6c6:       cf 93           push    r28
     6c8:       df 93           push    r29
     6ca:       8d e0           ldi     r24, 0x0D       ; 13
     6cc:       61 e0           ldi     r22, 0x01       ; 1
     6ce:       0e 94 23 02     call    0x446   ; 0x446 
     6d2:       04 c0           rjmp    .+8             ; 0x6dc 
     6d4:       8d ef           ldi     r24, 0xFD       ; 253
     6d6:       94 e0           ldi     r25, 0x04       ; 4
     6d8:       0e 94 25 06     call    0xc4a   ; 0xc4a <_ZN16MYOBJ7connectEv>
     6dc:       8d ef           ldi     r24, 0xFD       ; 253
     6de:       94 e0           ldi     r25, 0x04       ; 4
     6e0:       0e 94 21 06     call    0xc42   ; 0xc42 <_ZN16MYOBJ11isConnectedEv>
...

(I did try to build this code, and it did fail - it reads the 'line numbers' as labels)

Obviously, both listings (for the loop function, at least) represent the same assembly code; except:

The gcc one (should) compile -- the objdump one does not
The objdump one contains listings of all referred functions, which could be defined in files other than the 'master' (e.g., digitalWrite) -- the gcc one does not
The objdump one contains original C/C++ source lines 'interspersed' with assembly (but only occasionally, and seemingly only for C files?) -- the gcc one does not

So, is there a way to obtain an assembly listing that would be 'compilable', however with all in-linked functions, and where source C/C++ code is (possibly, where appropriate) interspersed as comments (so they don't interfere with compilation of assembly file)? (short of writing a parser for the output of objdump, that is :))

Spudd86 Spudd86 · Accepted Answer · 2011-08-04T18:35:45

Add the option -fverbose-asm to your gcc command line up there. (This is in the gcc manual, but it's documented under 'Code Gen Options')

GCC/objdump: Generating compilable/buildable assembly (interspersed with C/C++) source?

3 Answers