[Qemu-discuss] How to GDB step debug a dynamically linked executable in QEMU user mode?

[Ciro Santilli]

https://stackoverflow.com/questions/51310756/how-to-gdb-step-debug-a-dynamically-linked-executable-in-qemu-user-mode

For example for ARM, if I compile statically, all works fine:

    sudo apt-get install gdb-multiarch gcc-arm-linux-gnueabihf qemu-user
    printf '
    #include <stdio.h>
    #include <stdlib.h>

    int main() {
        puts("hello world");
        return EXIT_SUCCESS;
    }
    ' >  hello_world.c
    arm-linux-gnueabihf-gcc -ggdb3 -static -o hello_world hello_world.c
    qemu-arm -L /usr/arm-linux-gnueabihf -g 1234 ./hello_world

On another terminal:

    gdb-multiarch -q --nh \
      -ex 'set architecture arm' \
      -ex 'set sysroot /usr/arm-linux-gnueabihf' \
      -ex 'file hello_world' \
      -ex 'target remote localhost:1234' \
      -ex 'break main' \
      -ex continue \
    ;

This leaves me at `main`, and I can see the source and step debug as usual.

However, if I remove the `-static`, and keep everything else unchanged, my
breakpoint never gets hit, and the program runs until completion:

    The target architecture is assumed to be arm
    Reading symbols from hello_world...done.
    Remote debugging using localhost:1234
    Reading symbols from
/usr/arm-linux-gnueabihf/lib/ld-linux-armhf.so.3...(no debugging symbols
found)...done.
    0xff7b3b80 in ?? () from
/usr/arm-linux-gnueabihf/lib/ld-linux-armhf.so.3
    Breakpoint 1 at 0x50c: file hello_world.c, line 5.
    Continuing.
    [Inferior 1 (Remote target) exited normally]

The executable itself does work fine however:

    qemu-arm -L /usr/arm-linux-gnueabihf ./hello_world

prints:

    hello world

I have seen:
https://stackoverflow.com/questions/20590155/how-to-single-step-arm-assembler-in-gdb-on-qemu
but it didn't cover the case of dynamically linked executables specifically.

Tested on Ubuntu 18.04, gdb-multiarch 8.1-0ubuntu3, gcc-arm-linux-gnueabihf
4:7.3.0-3ubuntu2, qemu-user 1:2.11+dfsg-1ubuntu7.3.