failed xen attempt, refactor timer, failed svc attempt, aarch64 use gicv3

baremetal/arch/aarch64/svc.c

@@ -0,0 +1,28 @@
+#include <stdio.h>
+#include <inttypes.h>
+
+#include "common_aarch64.h"
+
+/* Masks each of the 4 exception types: Synchronous, System error,
+ * IRQ and FIQ.
+ */
+SYSREG_READ_WRITE(uint32_t, daif)
+
+/* Determines if we use SP0 or SPx. Default: SP0.
+ * See also: https://stackoverflow.com/questions/29393677/armv8-exception-vector-significance-of-el0-sp
+ */
+SYSREG_READ_WRITE(uint32_t, spsel)
+
+/* Jump to this SP if spsel == SPx. */
+SYSREG_READ_WRITE(uint64_t, sp_el1)
+
+int main(void) {
+    printf("daif 0x%" PRIx32 "\n", sysreg_daif_read());
+    printf("spsel 0x%" PRIx32 "\n", sysreg_spsel_read());
+    /* TODO this breaks execution because reading system registers that end
+     * in ELx "trap", leading into an exception on the upper EL.
+     */
+    /*printf("sp_el1 0x%" PRIx64 "\n", sysreg_sp_el1_read());*/
+    /*SVC(0);*/
+    return 0;
+}