Minimal bare metal project for Raspberry Pi 2 - https://williamdurand.fr/2021/01/23/bare-metal-raspberry-pi-2-programming/

boot.S

.section ".text.boot"

.globl _start
_start:
    # Setup the stack.
    mov sp, #0x8000

    bl kernel_main

halt:
    wfe
    b halt

.globl do_nothing
do_nothing:
    bx lr

kernel.c

#include <stdint.h>

#define GPFSEL4 0x3F200010
#define GPSET1 0x3F200020
#define GPCLR1 0x3F20002C

extern void do_nothing();

void kernel_main() {
  *(volatile uint32_t *)GPFSEL4 &= ~(7 << 21);
  *(volatile uint32_t *)GPFSEL4 |= 1 << 21;

  while (1) {
    *(volatile uint32_t *)GPSET1 = 1 << (47 - 32);

    for (uint32_t i = 0; i < 0x100000; i++) {
      do_nothing();
    }

    *(volatile uint32_t *)GPCLR1 = 1 << (47 - 32);

    for (uint32_t i = 0; i < 0x100000; i++) {
      do_nothing();
    }
  }
}

linker.ld

ENTRY(_start)

SECTIONS
{
    . = 0x8000;

    .text :
    {
        KEEP(*(.text.boot))
        *(.text*)
    }

    .rodata :
    {
        *(.rodata*)
        . = ALIGN(4K);
    }

    /DISCARD/ :
    {
        *(.comment)
    }
}

Makefile

default: all

CFLAGS = -mcpu=cortex-a7 -ffreestanding -nostdlib -fno-builtin -Wall -Wextra

all: kernel7.img

kernel7.img: kernel.elf
	arm-none-eabi-objcopy $< -O binary $@

kernel.elf: boot.o kernel.o
	arm-none-eabi-gcc $(CFLAGS) -T linker.ld -o $@ $^

boot.o: boot.S
	arm-none-eabi-gcc $(CFLAGS) -c $< -o $@

kernel.o: kernel.c
	arm-none-eabi-gcc $(CFLAGS) -c $< -o $@

clean:
	rm -f *.o *.img *.elf