ptrace: add demo tool to test overwriting syscall number

apps/test-ptrace-syscall.c

@@ -0,0 +1,69 @@
+#include <errno.h>
+#include <string.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <getopt.h>
+#include <signal.h>
+#include <sys/ptrace.h>
+#include <sys/wait.h>
+#include <sys/signal.h>
+#include <sys/signal_defs.h>
+#include <sys/sysfunc.h>
+#include <sys/utsname.h>
+#include <sys/time.h>
+#include <sys/socket.h>
+#include <sys/uregs.h>
+#include <syscall_nums.h>
+
+int main(int argc, char * argv[]) {
+	pid_t p = fork();
+	if (!p) {
+		if (ptrace(PTRACE_TRACEME, 0, NULL, NULL) < 0) {
+			fprintf(stderr, "%s: ptrace: %s\n", argv[0], strerror(errno));
+			return 1;
+		}
+		execvp(argv[optind], &argv[optind]);
+		return 1;
+	}
+
+	while (1) {
+		int status = 0;
+		pid_t res = waitpid(p, &status, WSTOPPED);
+
+		if (res < 0) {
+			fprintf(stderr, "%s: waitpid: %s\n", argv[0], strerror(errno));
+		} else {
+			if (WIFSTOPPED(status)) {
+				if (WSTOPSIG(status) == SIGTRAP) {
+					struct URegs regs;
+					ptrace(PTRACE_GETREGS, p, NULL, &regs);
+
+					/* Event type */
+					int event = (status >> 16) & 0xFF;
+					switch (event) {
+						case PTRACE_EVENT_SYSCALL_ENTER:
+							if (uregs_syscall_num(&regs) == SYS_SLEEP) {
+								fprintf(stderr, "%s: sleep called, rewriting to yield\n", argv[0]);
+								uregs_syscall_num(&regs) = SYS_YIELD;
+								ptrace(PTRACE_SETREGS, p, NULL, &regs);
+							}
+							break;
+						default:
+							break;
+					}
+					ptrace(PTRACE_CONT, p, NULL, NULL);
+				} else {
+					ptrace(PTRACE_CONT, p, NULL, (void*)(uintptr_t)WSTOPSIG(status));
+				}
+			} else if (WIFSIGNALED(status)) {
+				return 0;
+			} else if (WIFEXITED(status)) {
+				return 0;
+			}
+		}
+	}
+
+	return 0;
+}
+