coreboot-kgpe-d16/src/cpu/x86/lapic/boot_cpu.c

#include <cpu/x86/msr.h>

static int boot_cpu(void)
{
	int bsp;
	msr_t msr;
	msr = rdmsr(0x1b);
	bsp = !!(msr.lo & (1 << 8));
	return bsp;
}