test-user-mode: make perfect like build-userland

Multithreading and target selection.

userland/c/false.c

@@ -1,4 +1,5 @@
-/* Exit with status 1.
+/* Exit with status 1 like the POSIX false utility:
+ * http://pubs.opengroup.org/onlinepubs/9699919799/utilities/false.html
  *
  * Can be uesd to test that emulators forward the exit status properly.
  * https://github.com/cirosantilli/linux-kernel-module-cheat#gem5-syscall-emulation-exit-status

userland/c/infinite_loop.c

@@ -0,0 +1,29 @@
+/* Loop infinitely. Print an integer whenever a period is reached:
+ *
+ * ....
+ * ./infinite_loop [period]
+ * ....
+ */
+
+#include <inttypes.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(int argc, char **argv) {
+    uintmax_t i, j, period;
+    if (argc > 1) {
+        period = strtoumax(argv[1], NULL, 10);
+    } else {
+        period = 100000000;
+    }
+    i = 0;
+    j = 0;
+    while (1) {
+        i++;
+        if (i % period == 0) {
+            printf("%ju\n", j);
+            j++;
+        }
+    }
+}

userland/c/stderr.c

@@ -0,0 +1,7 @@
+/* Print hello to stderr. */
+
+#include <stdio.h>
+
+int main(void) {
+    fputs("hello\n", stderr);
+}

userland/cpp/bst_vs_heap.cpp

@@ -20,7 +20,7 @@ int main(int argc, char **argv) {
     if (argc > 1) {
         n = std::stoi(argv[1]);
     } else {
-        n = 1000;
+        n = 1;
     }
 
     // Action.