How do I write a given address to a register using inline assembly

Question

I have the following statement:

asm volatile("ldr r0, =0x10000");

Instead of writing 0x10000 I want to write a parameter so it will look like this:

uint32_t addr = 0x20000;
asm volatile("ldr r0, =addr");

how can I manage to do it?

i am using ARM processor.

I want to do this:

At the end I want to do this:

asm volatile("ldr r0, =0x10000");
asm volatile("ldr r0, [r0]");
asm volatile("mov sp, r0");

same for pc

thanks.

Answer 1

gcc is quite capable of generating those instructions so you can do:

void** p = 0x10000;
register void* sp asm("sp") = *p;
__asm__ __volatile__("" : : "r" (sp) : "memory");

Note it's dangerous to mess with sp so make sure you know what you are doing.

To load pc you will indeed need to use a mov such as:

void** p = 0x10000;
__asm__ __volatile__("mov pc, %0" : : "r" (*p) : "memory");
__builtin_unreachable();