In this post, we will emulate a baremetal program for Cortex-M on Ubuntu PC.

Installation

We will need

  1. QEMU emulator for ARM
  2. GDB

Fortunately both of them are available through Ubuntu software repository.

Install them using the following command:

sudo apt install qemu-system-arm
sudo apt install gdb-arm-none-eabi

Emulation

We will use QEMU for emulation. GDB is used to control and inspect QEMU.

Launch QEMU

qemu-system-arm -monitor stdio -machine lm3s811evb -cpu cortex-m3 -s -S -kernel startup.elf
  • -monitor stdio
    Access QEMU HMI monitor from terminal
  • -machine lm3s811evb -cpu cortex-m3
    Select machine lm3s811evb and CPU cortex-m3
  • -s
    Start GDB server on localhost:1234
  • -S
    Don’t start execution. This is used so we can start and control execution from GDB
  • -kernel startup.elf
    The executable file to execute

Launch GDB client

arm-none-eabi-gdb startup.elf

You should now be in GDB interactive console.

Connect to QEMU

Lets connect to GDB server hosted by QEMU from the GDB client

target remote localhost:1234
load

Run the program

continue

Inspect

Press <Ctrl-c> to stop execution.

Check registers

In lines 13, 14 and 16, we update registers r1, r0 and r2 respectively. They should hold values 0x20000000, 10 and 10 respectively.

info reg r0 r1 r2

Should print:

r0 0x20000000 536870912
r1 0xa 10
r2 0xa 10

Check memory

We write value 10 to memory address 0x20000000. Lets check if that worked correctly:

x/4wx 0x20000000

0x20000000: 0x0000000a 0x00000000 0x00000000 0x00000000