gdb misses breakpoint and stops one line after

Question

I am trying to debug a simple assembly language program in gdb and setting a breakpoint at the _start label(line 5), but when I run it, the program stops one line after on line 6, not on line 5.

I cannot find the reason for this behaviour on google or from my searches on the Raspbian bug database.

To repeat the steps below, run the program on a Raspberry Pi 3 running Raspbian 8.0 Jessie and gdb version 7.7.1

1 @filename: P2_1.s -- program adds contents of two registers together.
2 
3 .text
4 .global _start
5 _start:  MOV R1, #0x25     @storing 25 hex in R1
6          MOV R2, #0x34     @storing 34 hex in R2
7          ADD R3, R2, R1    @adding R1 and R2
8 HERE:   B   HERE           @infinite loop
9 .end    

Compile and link including debug symbols like this:

$ as -g -o P2_1.o P2_1.s; ld -o P2_1 P2_1.o

Then run gdb like this:

$ gdb P2_1

Then in gdb add a breakpoint at the _start label like this:

(gdb) break _start
Breakpoint 1 at 0x10058: file P2_1.s, line 6.

The breakpoint is added to line 6 not line 5. When you run it, it should stop at line 5, but it doesnt. It stops at line 6.

Is this normal behaviour of gdb or is it a bug?

Answer 1

This is not an actual solution to this question and I really do not think this question belong here. But here is what forum says.

1. http://sourceware.org/ml/gdb-patches/2012-08/msg00148.html

This is a pretty old post which says the similar issue reported by you.

2. Also there is a stackquestion as well here

https://stackoverflow.com/questions/11702143/why-does-gdb-stop-at-a-different-line-than-i-b-shows-while-returning-from-func

But interesting its something new for me as well. As far as people reported this issue has been there till 7.4 version.