Add test submission to check consistent CPU pinning

Ideally we should check that the submission is pinned to the CPU
core that we set, but that information is not as easily available.

Author: eldering

example_problems/hello/submissions/wrong_answer/test-cpu-pinning.c

@@ -0,0 +1,72 @@
+/*
+ * This code forks 10 children and checks that those run on the same
+ * CPU core as the parent. Since we're normally doing CPU pinning,
+ * this should be true and the program generates a WRONG-ANWSER.
+ * If there's a mismatch the program will trigger a RUNTIME-ERROR.
+ *
+ * @EXPECTED_RESULTS@: WRONG-ANSWER
+ */
+
+#include <errno.h>
+#include <unistd.h>
+#include <sched.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/wait.h>
+
+extern int errno;
+
+int main()
+{
+	unsigned int parent_cpu, cpu;
+	getcpu(&parent_cpu, NULL);
+	printf("Parent on CPU %d\n", parent_cpu);
+	fflush(NULL);
+
+	for(int i=0; i<10; i++) {
+		if ( fork()==0 ) {
+			// We're in the child
+			getcpu(&cpu, NULL);
+			printf("Child %d on CPU %d\n", i, cpu);
+			fflush(NULL);
+			if ( cpu!=parent_cpu ) {
+				printf("CPU MISMATCH!\n");
+				fflush(NULL);
+				return 1;
+			}
+			return 0;
+		}
+	}
+
+	// Wait for all our children
+	do {
+		pid_t pid;
+		int status;
+		pid = wait(&status);
+		if ( pid==-1 ) {
+			if ( errno==ECHILD ) {
+				printf("Done waiting for all children\n");
+			} else {
+				printf("Error in wait: %s\n", strerror(errno));
+			}
+			fflush(NULL);
+			break;
+		}
+		if ( pid>0 ) {
+			if ( !WIFEXITED(status) ) {
+				printf("Child pid %d terminated abnormally\n", (int)pid);
+				fflush(NULL);
+				return 1;
+			}
+			if ( WEXITSTATUS(status)!=0 ) {
+				printf("Child pid %d terminated with exit status %d\n",
+				       (int)pid, (int)WEXITSTATUS(status));
+				return 1;
+			}
+			printf("Child pid %d terminated\n", (int)pid);
+			fflush(NULL);
+		}
+	} while ( 1 );
+
+	return 0;
+}