baremetal: aarch64 semihosting exit

baremetal/arch/aarch64/semihost_exit.S

@@ -0,0 +1,20 @@
+.global main
+main:
+    /* 0x20026 == ADP_Stopped_ApplicationExit */
+    mov x1, #0x26
+    movk x1, #2, lsl #16
+    str x1, [sp,#0]
+
+    /* Exit status code. Host QEMU process exits with that status. */
+    mov x0, #0
+    str x0, [sp,#8]
+
+    /* x1 contains the address of parameter block.
+     * Any memory address could be used. */
+    mov x1, sp
+
+    /* SYS_EXIT */
+    mov w0, #0x18
+
+    /* Do the semihosting call on A64. */
+    hlt 0xf000

baremetal/arch/arm/semihost_exit.S

@@ -1,5 +1,8 @@
 .global main
 main:
+    /* SYS_EXIT */
     mov r0, #0x18
+    /* ADP_Stopped_ApplicationExit */
     ldr r1, =#0x20026
+    /* Do the semihosting call on A32. */
     svc 0x00123456