Calling ARM assembly from C, GCC (bare metal)

Question

I am trying to do some bare-metal programming in ARM with GCC and testing on QEMU. Whenever I call into an ARM label from C, my program hangs. I have a simple example of code

Answer 1

If you assemble your asm code as Thumb, you need to mark the function as a Thumb function, so that the linker uses correct instruction when branching to it (e.g. BLX or BX to an address with the low bit set). This is done with the .thumb_func directive:

.global activate
.thumb_func
activate:
    b test

Another option is to explicitly ask the assembler to generate ARM code:

.code 32
.global activate
activate:
    b test

Check this article too, although remember that current processors don't need many workarounds that were necessary in ARMv4, so you probably shouldn't follow it blindly.