5e: fix _tos->pid / libthread bug

sys/src/cmd/5e/fns.h

@@ -35,3 +35,4 @@ void invalid(u32int);
 void fpatransfer(u32int);
 void fpaoperation(u32int);
 void fparegtransfer(u32int);
+void inittos(void);

sys/src/cmd/5e/proc.c

@@ -108,8 +108,16 @@ initstack(int argc, char **argv)
 		ap += len;
 	}
 	*(ulong *) vaddrnol(sp, 4) = 0;
+	inittos();
+}
 
-	((Tos *) vaddrnol(tos, sizeof(Tos)))->pid = getpid();
+void
+inittos(void)
+{
+	ulong tos;
+
+	tos = mach->utop - sizeof(Tos) * 2;
+	((Tos *) vaddrnol(tos, sizeof(Tos)))->pid = P->pid;
 }
 
 static int

sys/src/cmd/5e/sys.c

@@ -401,6 +401,7 @@ sysrfork(void)
 		P = p;
 		atexit(cleanup);
 		P->pid = getpid();
+		inittos();
 		addproc(P);
 	}
 	P->R[0] = rc;