x86_64 cpu: syscall instruction

kernel-src/arch/x86-64/cpu.c

@@ -0,0 +1,32 @@
+#include <arch/cpu.h>
+#include <arch/apic.h>
+#include <cpuid.h>
+#include <logging.h>
+
+#define CPUID_SYSCALL (1 << 11)
+#define EFER_SYSCALLENABLE 1
+
+void arch_syscall_entry();
+
+void cpu_initstate() {
+	arch_apic_initap();
+
+	// syscall instruction
+	unsigned int eax = 0,ebx = 0,ecx = 0,edx = 0;
+	__get_cpuid(0x80000001, &eax, &ebx, &ecx, &edx);
+
+	// TODO in the future, have an alternative way of handling syscalls
+	__assert(edx & CPUID_SYSCALL);
+	uint64_t efer = rdmsr(MSR_EFER);
+	efer |= EFER_SYSCALLENABLE;
+	wrmsr(MSR_EFER, efer);
+
+	uint64_t star = 0;
+	star |= (uint64_t)0x13 << 48;
+	star |= (uint64_t)0x08 << 32;
+
+	wrmsr(MSR_STAR, star);
+	wrmsr(MSR_LSTAR, (uint64_t)arch_syscall_entry);
+	wrmsr(MSR_CSTAR, 0); // no compatibility mode syscall handler
+	wrmsr(MSR_FMASK, 0x200); // disable interrupts on syscall
+}