kernel: archctl syscall

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

@@ -0,0 +1,28 @@
+#include <kernel/syscalls.h>
+#include <arch/msr.h>
+#include <errno.h>
+
+#define ARCH_CTL_GSBASE 0
+#define ARCH_CTL_FSBASE 1
+
+syscallret_t syscall_archctl(context_t *context, int func, void *arg) {
+	syscallret_t ret = {
+		.errno = 0,
+		.ret = 0
+	};
+
+	switch (func) {
+		case ARCH_CTL_GSBASE:
+			// kernelgsbase because it will be switched out to user
+			wrmsr(MSR_KERNELGSBASE, (uint64_t)arg);
+			break;
+		case ARCH_CTL_FSBASE:
+			wrmsr(MSR_FSBASE, (uint64_t)arg);
+			break;
+		default:
+			ret.errno = EINVAL;
+			break;
+	}
+
+	return ret;
+}

kernel-src/arch/x86-64/syscall.asm

@@ -5,6 +5,7 @@ extern syscall_openat
 extern syscall_read
 extern syscall_seek
 extern syscall_close
+extern syscall_archctl
 syscalltab:
 dq syscall_print
 dq syscall_mmap
@@ -12,7 +13,8 @@ dq syscall_openat
 dq syscall_read
 dq syscall_seek
 dq syscall_close
-syscallcount equ 6
+dq syscall_archctl
+syscallcount equ 7
 section .text
 global arch_syscall_entry
 ; on entry: