Interleave disassembly + source with avr-objdump

Question

I have a C program for the attiny85, that I want to disassemble and display with interleaved source code.

Here's my program: test.c

#include <avr/io.h>
int main() {
 for(int i=0; i<100; i++) {
 PORTB=i;
 }
}

Here's how I compile it: avr-gcc -g -O0 -mmcu=attiny85 -o test.elf test.c

Finally, I generate the disassembly with interleaved source-code with the command: avr-objdump -S -D test.elf

The disassembly of the text section shows the following disassembly without interleaved source code:

00000030 <main>:
 30: cf 93 push r28
 32: df 93 push r29
 34: 00 d0 rcall .+0 ; 0x36 <main+0x6>
 36: cd b7 in r28, 0x3d ; 61
 38: de b7 in r29, 0x3e ; 62
 3a: 1a 82 std Y+2, r1 ; 0x02
 3c: 19 82 std Y+1, r1 ; 0x01
 3e: 0a c0 rjmp .+20 ; 0x54 <__SREG__+0x15>
 40: 88 e3 ldi r24, 0x38 ; 56
 42: 90 e0 ldi r25, 0x00 ; 0
 44: 29 81 ldd r18, Y+1 ; 0x01
 46: fc 01 movw r30, r24
 48: 20 83 st Z, r18
 4a: 89 81 ldd r24, Y+1 ; 0x01
 4c: 9a 81 ldd r25, Y+2 ; 0x02
 4e: 01 96 adiw r24, 0x01 ; 1
 50: 9a 83 std Y+2, r25 ; 0x02
 52: 89 83 std Y+1, r24 ; 0x01
 54: 89 81 ldd r24, Y+1 ; 0x01
 56: 9a 81 ldd r25, Y+2 ; 0x02
 58: 84 36 cpi r24, 0x64 ; 100
 5a: 91 05 cpc r25, r1
 5c: 8c f3 brlt .-30 ; 0x40 <__SREG__+0x1>
 5e: 80 e0 ldi r24, 0x00 ; 0
 60: 90 e0 ldi r25, 0x00 ; 0
 62: 0f 90 pop r0
 64: 0f 90 pop r0
 66: df 91 pop r29
 68: cf 91 pop r28
 6a: 08 95 ret

The disassembly makes somewhat sense, only that I miss the interleaved source code.

Interestingly enough, the output also includes a stab section, where I also find the main segment disassembled:

#include <avr/io.h>
int main() {
 30: 20 00 .word 0x0020 ; ????
 32: 00 00 nop
 34: 80 00 .word 0x0080 ; ????
 36: 00 00 nop
 38: 00 00 nop
 for(int i=0; i<100; i++) {
 3a: 00 00 nop
 3c: 40 00 .word 0x0040 ; ????
 3e: 00 00 nop
 PORTB=i;
 40: 80 00 .word 0x0080 ; ????
 42: 00 00 nop
 44: 00 00 nop
 46: 00 00 nop
 48: 5a 00 .word 0x005a ; ????
 for(int i=0; i<100; i++) {
 4a: 00 00 nop
 4c: 80 00 .word 0x0080 ; ????
 4e: 00 00 nop
 50: 00 00 nop
 52: 00 00 nop
 54: 91 00 .word 0x0091 ; ????
 56: 00 00 nop
 58: 80 00 .word 0x0080 ; ????
 5a: 00 00 nop
 5c: 00 00 nop
 5e: 00 00 nop
 60: b7 00 .word 0x00b7 ; ????
 }
}

Now the output includes source code, but the disassembly is wrong.

How do I get an output were both is correct: the disassembled instructions and the interleaved source-code?

(avr-gcc (GCC) 9.3.0. Interleave Assembly and Source for avr-objdump does not seem to have the problem, although he's using the same compiler flags...)

Answer 1

The .stabs section contains debugging info, not actual code. There is no point in trying to "disassemble" it. The -D option of avr-objdump means "disassemble everything, whether or not you believe it's machine code". Not what you want. For your purpose, -S should be enough.

I do not know why your main() is displayed without source code. I tried your exact same program with the exact same commands and I do see the source interleaved with the assembly. I am using avr-gcc 5.4.0 and avr-objdump 2.26.20160125 as shipped on Ubuntu Eoan.

• Timo: Thanks. Indeed, if I downgrade the compiler to 5.4.0 it works as well. I'll try to pinpoint the version that introduced the problem and report a bug once I'm able to reproduce it in a clean environment.