Properly handle real SIGTRAPs.

* defs.h (ptrace_setoptions): Variable renamed to ptrace_setoptions_followfork.
* process.c (internal_fork): Ditto.
* strace.c (ptrace_setoptions_for_all): New variable.
(SYSCALLTRAP): New variable.
(error_msg_and_die): New function.
(test_ptrace_setoptions_for_all): New function.
(main): Call test_ptrace_setoptions_for_all() at init.
(handle_ptrace_event): Handle PTRACE_EVENT_EXEC (by ignoring it).
(trace): Check events and set ptrace options without -f too.
Check WSTOPSIG(status) not for SIGTRAP, but for SYSCALLTRAP.

defs.h

@@ -504,7 +504,7 @@ typedef enum {
 extern struct tcb **tcbtab;
 extern int *qual_flags;
 extern int debug, followfork;
-extern unsigned int ptrace_setoptions;
+extern unsigned int ptrace_setoptions_followfork;
 extern int dtime, xflag, qflag;
 extern cflag_t cflag;
 extern int acolumn;

process.c

@@ -915,7 +915,7 @@ Process %u resumed (parent %d ready)\n",
 int
 internal_fork(struct tcb *tcp)
 {
-	if ((ptrace_setoptions
+	if ((ptrace_setoptions_followfork
 	    & (PTRACE_O_TRACECLONE | PTRACE_O_TRACEFORK | PTRACE_O_TRACEVFORK))
 	   == (PTRACE_O_TRACECLONE | PTRACE_O_TRACEFORK | PTRACE_O_TRACEVFORK))
 		return 0;

strace.c

@@ -33,6 +33,7 @@
 #include "defs.h"
 
 #include <sys/types.h>
+#include <stdarg.h>
 #include <signal.h>
 #include <errno.h>
 #include <sys/param.h>
@@ -83,7 +84,10 @@ extern char *optarg;
 
 
 int debug = 0, followfork = 0;
-unsigned int ptrace_setoptions = 0;
+unsigned int ptrace_setoptions_followfork = 0;
+static unsigned int ptrace_setoptions_for_all = 0;
+/* Which WSTOPSIG(status) value marks syscall traps? */
+static unsigned int SYSCALLTRAP = SIGTRAP;
 int dtime = 0, xflag = 0, qflag = 0;
 cflag_t cflag = CFLAG_NONE;
 static int iflag = 0, interactive = 0, pflag_seen = 0, rflag = 0, tflag = 0;
@@ -211,6 +215,31 @@ usage: strace [-CdDffhiqrtttTvVxxy] [-a column] [-e expr] ... [-o file]\n\
 	exit(exitval);
 }
 
+static void error_msg_and_die(const char *fmt, ...)
+#if defined __GNUC__
+	__attribute__ ((noreturn, format(printf, 1, 2)))
+#endif
+;
+static void error_msg_and_die(const char *fmt, ...)
+{
+	char *msg;
+	va_list p;
+
+	va_start(p, fmt);
+	msg = NULL;
+	vasprintf(&msg, fmt, p);
+	if (msg) {
+		fprintf(stderr, "%s: %s\n", progname, msg);
+		free(msg);
+	}
+	va_end(p);
+
+	/* TODO? cflag = 0; -- or else cleanup() may print summary */
+	cleanup();
+	fflush(NULL);
+	_exit(1);
+}
+
 #ifdef SVR4
 #ifdef MIPS
 void
@@ -702,7 +731,7 @@ startup_child (char **argv)
  * and then see which options are supported by the kernel.
  */
 static int
-test_ptrace_setoptions(void)
+test_ptrace_setoptions_followfork(void)
 {
 	int pid, expected_grandchild = 0, found_grandchild = 0;
 	const unsigned int test_options = PTRACE_O_TRACECLONE |
@@ -727,7 +756,7 @@ test_ptrace_setoptions(void)
 				continue;
 			else if (errno == ECHILD)
 				break;
-			perror("test_ptrace_setoptions");
+			perror("test_ptrace_setoptions_followfork");
 			return -1;
 		}
 		if (tracee_pid != pid) {
@@ -761,9 +790,91 @@ test_ptrace_setoptions(void)
 		}
 	}
 	if (expected_grandchild && expected_grandchild == found_grandchild)
-		ptrace_setoptions |= test_options;
+		ptrace_setoptions_followfork |= test_options;
 	return 0;
 }
+
+/*
+ * Test whether the kernel support PTRACE_O_TRACESYSGOOD.
+ * First fork a new child, call ptrace(PTRACE_SETOPTIONS) on it,
+ * and then see whether it will stop with (SIGTRAP | 0x80).
+ *
+ * Use of this option enables correct handling of user-generated SIGTRAPs,
+ * and SIGTRAPs generated by special instructions such as int3 on x86:
+ * _start:	.globl	_start
+ *		int3
+ *		movl	$42, %ebx
+ *		movl	$1, %eax
+ *		int	$0x80
+ * (compile with: "gcc -nostartfiles -nostdlib -o int3 int3.S")
+ */
+static void
+test_ptrace_setoptions_for_all(void)
+{
+	const unsigned int test_options = PTRACE_O_TRACESYSGOOD | PTRACE_O_TRACEEXEC;
+	int pid;
+	int it_worked = 0;
+
+	pid = fork();
+	if (pid < 0)
+		error_msg_and_die("fork failed");
+
+	if (pid == 0) {
+		pid = getpid();
+		if (ptrace(PTRACE_TRACEME, 0L, 0L, 0L) < 0)
+			/* "parent, something is deeply wrong!" */
+			kill(pid, SIGKILL);
+		kill(pid, SIGSTOP);
+		_exit(0); /* parent should see entry into this syscall */
+	}
+
+	while (1) {
+		int status, tracee_pid;
+
+		errno = 0;
+		tracee_pid = wait(&status);
+		if (tracee_pid <= 0) {
+			if (errno == EINTR)
+				continue;
+			kill(pid, SIGKILL);
+			error_msg_and_die("%s: unexpected wait result %d", __func__, tracee_pid);
+		}
+		if (WIFEXITED(status))
+			break;
+		if (!WIFSTOPPED(status)) {
+			kill(pid, SIGKILL);
+			error_msg_and_die("%s: unexpected wait status %x", __func__, status);
+		}
+		if (WSTOPSIG(status) == SIGSTOP) {
+			/*
+			 * We don't check "options aren't accepted" error.
+			 * If it happens, we'll never get (SIGTRAP | 0x80),
+			 * and thus will decide to not use the option.
+			 * IOW: the outcome of the test will be correct.
+			 */
+			ptrace(PTRACE_SETOPTIONS, pid, 0L, test_options);
+		}
+		if (WSTOPSIG(status) == (SIGTRAP | 0x80)) {
+			it_worked = 1;
+		}
+		if (ptrace(PTRACE_SYSCALL, pid, 0L, 0L) < 0) {
+			kill(pid, SIGKILL);
+			error_msg_and_die("PTRACE_SYSCALL doesn't work");
+		}
+	}
+
+	if (it_worked) {
+		SYSCALLTRAP = (SIGTRAP | 0x80);
+		ptrace_setoptions_for_all = test_options;
+		if (debug)
+			fprintf(stderr, "ptrace_setoptions_for_all = %#x\n",
+				ptrace_setoptions_for_all);
+		return;
+	}
+
+	fprintf(stderr,
+		"Test for PTRACE_O_TRACESYSGOOD failed, giving up using this feature.\n");
+}
 #endif
 
 int
@@ -977,16 +1088,17 @@ main(int argc, char *argv[])
 
 #ifdef LINUX
 	if (followfork) {
-		if (test_ptrace_setoptions() < 0) {
+		if (test_ptrace_setoptions_followfork() < 0) {
 			fprintf(stderr,
 				"Test for options supported by PTRACE_SETOPTIONS "
 				"failed, giving up using this feature.\n");
-			ptrace_setoptions = 0;
+			ptrace_setoptions_followfork = 0;
 		}
 		if (debug)
-			fprintf(stderr, "ptrace_setoptions = %#x\n",
+			fprintf(stderr, "ptrace_setoptions_followfork = %#x\n",
-				ptrace_setoptions);
+				ptrace_setoptions_followfork);
 	}
+	test_ptrace_setoptions_for_all();
 #endif
 
 	/* Check if they want to redirect the output. */
@@ -1751,7 +1863,7 @@ int sig;
 				break;
 			}
 			error = ptrace_restart(PTRACE_CONT, tcp,
-					WSTOPSIG(status) == SIGTRAP ? 0
+					WSTOPSIG(status) == SYSCALLTRAP ? 0
 					: WSTOPSIG(status));
 			if (error < 0)
 				break;
@@ -2408,6 +2520,11 @@ handle_ptrace_event(int status, struct tcb *tcp)
 		}
 		return handle_new_child(tcp, childpid, 0);
 	}
+	if (status >> 16 == PTRACE_EVENT_EXEC) {
+		if (debug)
+			fprintf(stderr, "PTRACE_EVENT_EXEC on pid %d (ignored)\n", tcp->pid);
+		return 0;
+	}
 	return 1;
 }
 #endif
@@ -2597,7 +2714,7 @@ Process %d attached (waiting for parent)\n",
 			fprintf(stderr, "pid %u stopped, [%s]\n",
 				pid, signame(WSTOPSIG(status)));
 
-		if (ptrace_setoptions && (status >> 16)) {
+		if (status >> 16) {
 			if (handle_ptrace_event(status, tcp) != 1)
 				goto tracing;
 		}
@@ -2630,16 +2747,24 @@ Process %d attached (waiting for parent)\n",
 				}
 			}
 #ifdef LINUX
-			if (followfork && (tcp->parent == NULL) && ptrace_setoptions)
+			int options = ptrace_setoptions_for_all;
-				if (ptrace(PTRACE_SETOPTIONS, tcp->pid,
+			if (followfork && (tcp->parent == NULL))
-					   NULL, ptrace_setoptions) < 0 &&
+				options |= ptrace_setoptions_followfork;
-				    errno != ESRCH)
+			if (options) {
-					ptrace_setoptions = 0;
+				if (debug)
+					fprintf(stderr, "setting opts %x on pid %d\n", options, tcp->pid);
+				if (ptrace(PTRACE_SETOPTIONS, tcp->pid, NULL, options) < 0) {
+					if (errno != ESRCH) {
+						/* Should never happen, really */
+						error_msg_and_die("PTRACE_SETOPTIONS");
+					}
+				}
+			}
 #endif
 			goto tracing;
 		}
 
-		if (WSTOPSIG(status) != SIGTRAP) {
+		if (WSTOPSIG(status) != SYSCALLTRAP) {
 			if (WSTOPSIG(status) == SIGSTOP &&
 					(tcp->flags & TCB_SIGTRAPPED)) {
 				/*