first usable version of kernel and commands

After an year of hard work, this is a first "usable" version of Jehanne.

qa/kern/noexecmem.c

@@ -0,0 +1,100 @@
+#include <u.h>
+#include <libc.h>
+#define RET 0xc3
+
+int success;
+int cases;
+
+void
+handler(void *v, char *s)
+{
+	success++;
+	exits("PASS");
+}
+
+void
+callinsn(char *name, char *buf)
+{
+	void (*f)(void);
+	if (notify(handler)){
+		fprint(2, "%r\n");
+		exits("notify fails");
+	}
+
+
+	f = (void *)buf;
+	f();
+	print("FAIL %s\n", name);
+	exits("FAIL");
+}
+
+void
+writeptr(char *name, void *ptr)
+{
+	if (notify(handler)){
+		fprint(2, "%r\n");
+		exits("notify fails");
+	}
+
+	*(uintptr_t*)ptr = 0xdeadbeef;
+	print("FAIL %s\n", name);
+	exits("FAIL");
+}
+
+void
+main(void)
+{
+	char *str = "hello world";
+	char stk[128];
+	char *mem;
+
+	switch(rfork(RFMEM|RFPROC)){
+	case -1:
+		sysfatal("rfork");
+	case 0:
+		stk[0] = RET;
+		callinsn("exec stack", stk);
+	default:
+		cases++;
+		waitpid();
+	}
+
+	switch(rfork(RFMEM|RFPROC)){
+	case -1:
+		sysfatal("rfork");
+	case 0:
+		mem = malloc(128);
+		mem[0] = RET;
+		callinsn("exec heap", mem);
+	default:
+		cases++;
+		waitpid();
+	}
+
+	switch(rfork(RFMEM|RFPROC)){
+	case -1:
+		sysfatal("rfork");
+	case 0:
+		writeptr("write code", (void*)&main);
+	default:
+		cases++;
+		waitpid();
+	}
+
+	switch(rfork(RFMEM|RFPROC)){
+	case -1:
+		sysfatal("rfork");
+	case 0:
+		writeptr("write rodata", (void*)str);
+	default:
+		cases++;
+		waitpid();
+	}
+
+	if(success == cases){
+		print("PASS\n");
+		exits("PASS");
+	}
+	print("FAIL\n");
+	exits("FAIL");
+}