Add initial Darwin ARM64 context switching support

arm64-ucontext.h

@@ -0,0 +1,30 @@
+#define	setcontext(u)	_setmcontext(&(u)->mc)
+#define	getcontext(u)	_getmcontext(&(u)->mc)
+typedef struct mcontext mcontext_t;
+typedef struct ucontext ucontext_t;
+struct mcontext
+{
+    ulong gpr[10];   /* x19-x28 */
+    ulong fp;        /* x29 */
+    ulong lr;        /* x30 */
+    ulong sp;        /* stack pointer */
+    ulong x0;        /* return value / first argument */
+    ulong x1;        /* second argument */
+    ulong fpr[8];    /* d8-d15 */
+};
+
+struct ucontext
+{
+	struct {
+		void *ss_sp;
+		uint ss_size;
+	} uc_stack;
+	sigset_t uc_sigmask;
+	mcontext_t mc;
+};
+
+void makecontext(ucontext_t*, void(*)(void), int, ...);
+int swapcontext(ucontext_t*, const ucontext_t*);
+int _getmcontext(mcontext_t*);
+void _setmcontext(const mcontext_t*);
+

asm.S

@@ -13,7 +13,11 @@
 #endif
 
 #if defined(__APPLE__)
-#if defined(__i386__)
+#if defined(__aarch64__) || defined(__arm64__)
+#define NEEDARM64CONTEXT 1
+#define SET __setmcontext
+#define GET __getmcontext
+#elif defined(__i386__)
 #define NEEDX86CONTEXT 1
 #define SET _setmcontext
 #define GET _getmcontext
@@ -46,6 +50,77 @@
 #define GET getmcontext
 #endif
 
+#ifdef NEEDARM64CONTEXT
+
+.text
+.p2align 2
+
+.globl GET
+GET:
+    /* Save callee-saved general-purpose registers */
+    stp x19, x20, [x0, #0]
+    stp x21, x22, [x0, #16]
+    stp x23, x24, [x0, #32]
+    stp x25, x26, [x0, #48]
+    stp x27, x28, [x0, #64]
+
+    /* Save frame pointer and link register */
+    stp x29, x30, [x0, #80]
+
+    /* Save stack pointer */
+    mov x9, sp
+    str x9, [x0, #96]
+
+    /* Return 1 when this context is restored */
+    mov x9, #1
+    str x9, [x0, #104]
+    str x1, [x0, #112]
+
+    /* Save callee-saved floating-point registers */
+    stp d8, d9, [x0, #120]
+    stp d10, d11, [x0, #136]
+    stp d12, d13, [x0, #152]
+    stp d14, d15, [x0, #168]
+
+    /* First getcontext call returns 0 */
+    mov w0, #0
+    ret
+
+
+.globl SET
+SET:
+    /* x0 points to mcontext */
+    mov x9, x0
+
+    /* Restore general-purpose registers */
+    ldp x19, x20, [x9, #0]
+    ldp x21, x22, [x9, #16]
+    ldp x23, x24, [x9, #32]
+    ldp x25, x26, [x9, #48]
+    ldp x27, x28, [x9, #64]
+
+    /* Restore frame pointer and return address */
+    ldp x29, x30, [x9, #80]
+
+    /* Restore stack pointer */
+    ldr x10, [x9, #96]
+
+    /* Restore floating-point registers */
+    ldp d8, d9, [x9, #120]
+    ldp d10, d11, [x9, #136]
+    ldp d12, d13, [x9, #152]
+    ldp d14, d15, [x9, #168]
+
+    mov sp, x10
+
+    /* Restore return value / task arguments */
+    ldr x0, [x9, #104]
+    ldr x1, [x9, #112]
+
+    ret
+
+#endif
+
 #ifdef NEEDX86CONTEXT
 .globl SET
 SET:

context.c

@@ -3,7 +3,10 @@
 #include "taskimpl.h"
 
 #if defined(__APPLE__)
-#if defined(__i386__)
+#if defined(__aarch64__) || defined(__arm64__)
+#define NEEDARM64MAKECONTEXT
+#define NEEDSWAPCONTEXT
+#elif defined(__i386__)
 #define NEEDX86MAKECONTEXT
 #define NEEDSWAPCONTEXT
 #elif defined(__x86_64__)
@@ -40,6 +43,37 @@
 #define	NEEDMIPSMAKECONTEXT
 #endif
 
+#ifdef NEEDARM64MAKECONTEXT
+
+void
+makecontext(ucontext_t *ucp, void (*func)(void), int argc, ...)
+{
+    uintptr_t sp;
+    va_list arg;
+
+    if(argc != 2){
+        fprint(2, "makecontext: expected 2 arguments\n");
+        abort();
+    }
+
+    sp = (uintptr_t)ucp->uc_stack.ss_sp
+        + ucp->uc_stack.ss_size;
+
+    sp &= ~(uintptr_t)0xF;
+
+    memset(&ucp->mc, 0, sizeof ucp->mc);
+
+    ucp->mc.sp = (ulong)sp;
+    ucp->mc.lr = (ulong)(uintptr_t)func;
+
+    va_start(arg, argc);
+    ucp->mc.x0 = va_arg(arg, uint);
+    ucp->mc.x1 = va_arg(arg, uint);
+    va_end(arg);
+}
+
+#endif
+
 #ifdef NEEDPOWERMAKECONTEXT
 void
 makecontext(ucontext_t *ucp, void (*func)(void), int argc, ...)

taskimpl.h

@@ -127,6 +127,8 @@ extern	void		makecontext(ucontext_t*, void(*)(), int, ...);
 #		include "386-ucontext.h"
 #	elif defined(__x86_64__)
 #		include "amd64-ucontext.h"
+#	elif defined(__aarch64__) || defined (__arm64__)
+#		include "arm64-ucontext.h"
 #	else
 #		include "power-ucontext.h"
 #	endif