Various tweaks to make things run on Mac OS.

The main change is the use of pthread to implement ffork.

src/libthread/getpid.c

@@ -1,8 +1,7 @@
 #include "threadimpl.h"
-#include <unistd.h>
-
+extern int getfforkid(void);
 int
 _threadgetpid(void)
 {
-	return getpid();
+	return getfforkid();
 }

src/libthread/label.h

@@ -17,6 +17,21 @@ struct Label
 	ulong si;
 	ulong di;
 };
+#elif defined(__APPLE__)
+struct Label
+{
+	ulong	pc;		/* lr */
+	ulong	cr;		/* mfcr */
+	ulong	ctr;		/* mfcr */
+	ulong	xer;		/* mfcr */
+	ulong	sp;		/* callee saved: r1 */
+	ulong	toc;		/* callee saved: r2 */
+	ulong	gpr[19];	/* callee saved: r13-r31 */
+// XXX: currently do not save vector registers or floating-point state
+//	ulong	pad;
+//	uvlong	fpr[18];	/* callee saved: f14-f31 */
+//	ulong	vr[4*12];	/* callee saved: v20-v31, 256-bits each */
+};
 #else
 #error "Unknown or unsupported architecture"
 #endif

src/libthread/trend.c

@@ -25,7 +25,7 @@ threadmain(int argc, char **argv)
 	c[1] = chancreate(sizeof(ulong), 1);
 	c[2] = c[0];
 
-	threadcreate(pingpong, c, 16384);
+	proccreate(pingpong, c, 16384);
 	threadcreate(pingpong, c+1, 16384);
 	sendul(c[0], atoi(argv[1]));
 }