Debugging ARM binary on Ubuntu Host using qemu ARM and GDB

Now lets try to create simple helloworld program,

$ vim helloworld.c

#include <stdio.h>

int main(int argc, char **argv) {
        int num = 0;
        printf("helloworld\n");
        printf("addition: %d\n", 3+2);
        return 0;
}

Above simple program prints helloworld and also prints addition of two numbers. We will compile this program using below command,

$ arm-linux-gnueabihf-gcc -o helloworld helloworld.c -static -g

here as you can see,

• Notice, here we used “arm-linux-gnueabihf-gcc” installed on Ubuntu machine instead of toolchain GCC, since to avoid library mismatches, we need to use the toolchain installed on Ubuntu and that too with -static option to be able to successfully debug with qemu-arm.
• we also have added “-static” since we will be running this program inside qemu, it seems there is no correct library versions matched between the toolchain we have used to compile helloworld and how qemu-arm works and also when we tried to run helloworld compiled without -static, our program got crashed always.
• The ending “-g” is used to add the debugging symbols which will be required for debugging with GDB.

Now we can run the program with qemu-arm as,

$ qemu-arm -L gcc-arm-none-eabi-10-2020-q4-major/lib -g 8090 ./helloworld

this command will wait for the debugger to connect on port 8090, here you can use any port.

$ arm-none-eabi-gdb

(gdb) file helloworld
Reading symbols from helloworld...

(gdb) target remote:8090
Remote debugging using :8090
0x0000816c in _start ()

(gdb) break main

(gdb) c
Continuing.

Breakpoint 1, main (argc=1, argv=0xfffef184) at helloworld_src/helloworld.c:6
6		int num = 0;

(gdb) c
Continuing.
[Inferior 1 (process 1) exited normally]

$ qemu-arm -L gcc-arm-none-eabi-10-2020-q4-major/lib -g 8090 ./helloworld
helloworld
addition: 5