Add waitpid and execve

buildtest.c

@@ -34,10 +34,24 @@ int main(int argc, char* argv[]) {
   uint64_t pid = fork();
   // Print the pid in hex
   printhex(pid);
-
-  // Child process exits
-  if(pid == 0) return 0;
-  //TODO: wait on child to remove zombie process
+  // Child process
+  if (pid == 0) {
+    const char *progname = "/bin/sh";
+    const char *argv[4] = {
+        progname,
+        "-c",
+        "echo hi from sh",
+        0,
+    };
+    const char **envp = {0};
+    int32_t err = execve(progname, argv, envp);
+    // return with error code if execve fails
+    return err;
+  } 
+  int status; // Note: this is not JUST the exit code of the child
+  waitpid(pid, &status, 0);
+  print("Child wstatus: ");
+  printhex((uint64_t)status);
 
   // Test the read syscall
   #define INPUT_BUFFER_LEN 4096