[PATCH 4/4] Add conditionally enabled PTRACE_SEIZE support

Denys Vlasenko dvlasenk at redhat.com
Fri Sep 2 14:18:13 UTC 2011


> Patch 4: Add conditionally enabled SEIZE support.


diff -d -urpN strace.4/defs.h strace.5/defs.h
--- strace.4/defs.h	2011-09-02 11:23:45.242545628 +0200
+++ strace.5/defs.h	2011-09-02 14:48:08.945064165 +0200
@@ -383,6 +383,23 @@ extern int mp_ioctl(int f, int c, void *
 # if !HAVE_DECL_PTRACE_EVENT_EXIT
 #  define PTRACE_EVENT_EXIT	6
 # endif
+
+/* Experimental code using PTRACE_SEIZE can be enabled here: */
+//# define USE_SEIZE 1
+
+# ifdef USE_SEIZE
+#  undef PTRACE_SEIZE
+#  define PTRACE_SEIZE		0x4206
+#  undef PTRACE_INTERRUPT
+#  define PTRACE_INTERRUPT	0x4207
+#  undef PTRACE_LISTEN
+#  define PTRACE_LISTEN		0x4208
+#  undef PTRACE_SEIZE_DEVEL
+#  define PTRACE_SEIZE_DEVEL	0x80000000
+#  undef PTRACE_EVENT_STOP
+#  define PTRACE_EVENT_STOP	7
+# endif
+
 #endif /* LINUX */
 
 #if !defined __GNUC__
diff -d -urpN strace.4/strace.c strace.5/strace.c
--- strace.4/strace.c	2011-09-02 16:06:21.864293092 +0200
+++ strace.5/strace.c	2011-09-02 15:13:34.464884693 +0200
@@ -101,6 +101,14 @@ static int iflag = 0, interactive = 0, p
  */
 static bool daemonized_tracer = 0;
 
+#ifdef USE_SEIZE
+static int post_attach_sigstop = TCB_IGNORE_ONE_SIGSTOP;
+# define use_seize (post_attach_sigstop == 0)
+#else
+# define post_attach_sigstop TCB_IGNORE_ONE_SIGSTOP
+# define use_seize 0
+#endif
+
 /* Sometimes we want to print only succeeding syscalls. */
 int not_failing_only = 0;
 
@@ -290,6 +298,23 @@ foobar()
 # define fork()         vfork()
 #endif
 
+#ifdef USE_SEIZE
+static int
+ptrace_attach_or_seize(int pid)
+{
+	int r;
+	if (!use_seize)
+		return ptrace(PTRACE_ATTACH, pid, 0, 0);
+	r = ptrace(PTRACE_SEIZE, pid, 0, PTRACE_SEIZE_DEVEL);
+	if (r)
+		return r;
+	r = ptrace(PTRACE_INTERRUPT, pid, 0, 0);
+	return r;
+}
+#else
+# define ptrace_attach_or_seize(pid) ptrace(PTRACE_ATTACH, (pid), 0, 0)
+#endif
+
 static void
 set_cloexec_flag(int fd)
 {
@@ -480,7 +505,7 @@ startup_attach(void)
 					if (tid <= 0)
 						continue;
 					++ntid;
-					if (ptrace(PTRACE_ATTACH, tid, (char *) 1, 0) < 0) {
+					if (ptrace_attach_or_seize(tid) < 0) {
 						++nerr;
 						if (debug)
 							fprintf(stderr, "attach to pid %d failed\n", tid);
@@ -491,7 +516,7 @@ startup_attach(void)
 					cur_tcp = tcp;
 					if (tid != tcp->pid)
 						cur_tcp = alloctcb(tid);
-					cur_tcp->flags |= TCB_ATTACHED | TCB_STARTUP | TCB_IGNORE_ONE_SIGSTOP;
+					cur_tcp->flags |= TCB_ATTACHED | TCB_STARTUP | post_attach_sigstop;
 				}
 				closedir(dir);
 				if (interactive) {
@@ -523,12 +548,12 @@ startup_attach(void)
 			} /* if (opendir worked) */
 		} /* if (-f) */
 # endif /* LINUX */
-		if (ptrace(PTRACE_ATTACH, tcp->pid, (char *) 1, 0) < 0) {
+		if (ptrace_attach_or_seize(tcp->pid) < 0) {
 			perror("attach: ptrace(PTRACE_ATTACH, ...)");
 			droptcb(tcp);
 			continue;
 		}
-		tcp->flags |= TCB_STARTUP | TCB_IGNORE_ONE_SIGSTOP;
+		tcp->flags |= TCB_STARTUP | post_attach_sigstop;
 		if (debug)
 			fprintf(stderr, "attach to pid %d (main) succeeded\n", tcp->pid);
 
@@ -644,12 +669,10 @@ startup_child(char **argv)
 		kill(pid, SIGSTOP);
 # endif
 #else /* !USE_PROCFS */
-		if (!daemonized_tracer) {
+		if (!daemonized_tracer && !use_seize) {
 			if (ptrace(PTRACE_TRACEME, 0, (char *) 1, 0) < 0) {
 				perror_msg_and_die("ptrace(PTRACE_TRACEME, ...)");
 			}
-			if (debug)
-				kill(pid, SIGSTOP);
 		}
 
 		if (username != NULL) {
@@ -713,9 +736,32 @@ startup_child(char **argv)
 	/* We are the tracer */
 
 	if (!daemonized_tracer) {
+///
+		if (use_seize) {
+			if (!strace_vforked) {
+				/* Wait until child stopped itself */
+				int status;
+				while (waitpid(pid, &status, WSTOPPED) < 0) {
+					if (errno == EINTR)
+						continue;
+					perror_msg_and_die("waitpid");
+				}
+				if (!WIFSTOPPED(status) || WSTOPSIG(status) != SIGSTOP) {
+					kill(pid, SIGKILL);
+					perror_msg_and_die("Unexpected wait status %x", status);
+				}
+fprintf(stderr, "Pid %d stopped, attaching\n", pid);
+			}
+			if (ptrace_attach_or_seize(pid)) {
+				kill(pid, SIGKILL);
+				perror_msg_and_die("Can't attach to %d", pid);
+			}
+			if (!strace_vforked)
+				kill(pid, SIGCONT);
+		}
 		tcp = alloctcb(pid);
 		if (!strace_vforked)
-			tcp->flags |= TCB_STARTUP | TCB_IGNORE_ONE_SIGSTOP;
+			tcp->flags |= TCB_STARTUP | post_attach_sigstop;
 		else
 			tcp->flags |= TCB_STARTUP;
 	}
@@ -943,6 +989,55 @@ test_ptrace_setoptions_for_all(void)
 	error_msg("Test for PTRACE_O_TRACESYSGOOD failed, "
 		  "giving up using this feature.");
 }
+
+# ifdef USE_SEIZE
+static void
+test_ptrace_seize(void)
+{
+	int pid;
+
+	pid = fork();
+	if (pid < 0)
+		perror_msg_and_die("fork");
+
+	if (pid == 0) {
+		pause();
+		_exit(0);
+	}
+
+	/* PTRACE_SEIZE, unlike ATTACH, doesn't force tracee to trap.  After
+	 * attaching tracee continues to run unless a trap condition occurs.
+	 * PTRACE_SEIZE doesn't affect signal or group stop state.
+	 */
+	if (ptrace(PTRACE_SEIZE, pid, 0, PTRACE_SEIZE_DEVEL) == 0) {
+		post_attach_sigstop = 0; /* this sets use_seize to 1 */
+	}
+else fprintf(stderr, "PTRACE_SEIZE doesn't work\n");
+
+	kill(pid, SIGKILL);
+
+	while (1) {
+		int status, tracee_pid;
+
+		errno = 0;
+		tracee_pid = waitpid(pid, &status, 0);
+		if (tracee_pid <= 0) {
+			if (errno == EINTR)
+				continue;
+			perror_msg_and_die("%s: unexpected wait result %d",
+					 __func__, tracee_pid);
+		}
+		if (WIFSIGNALED(status)) {
+			return;
+		}
+		error_msg_and_die("%s: unexpected wait status %x",
+				__func__, status);
+	}
+}
+# else /* !USE_SEIZE */
+#  define test_ptrace_seize() ((void)0)
+# endif
+
 #endif
 
 int
@@ -1143,6 +1238,7 @@ main(int argc, char *argv[])
 	if (followfork)
 		test_ptrace_setoptions_followfork();
 	test_ptrace_setoptions_for_all();
+	test_ptrace_seize();
 #endif
 
 	/* Check if they want to redirect the output. */
@@ -1687,7 +1783,7 @@ detach(struct tcb *tcp, int sig)
 #define PTRACE_DETACH PTRACE_SUNDETACH
 #endif
 	/*
-	 * We did PTRACE_ATTACH but possibly didn't see the expected SIGSTOP.
+	 * We attached but possibly didn't see the expected SIGSTOP.
 	 * We must catch exactly one as otherwise the detached process
 	 * would be left stopped (process state T).
 	 */
@@ -2421,7 +2517,7 @@ trace()
 				   child so that we know how to do clearbpt
 				   in the child.  */
 				tcp = alloctcb(pid);
-				tcp->flags |= TCB_ATTACHED | TCB_STARTUP | TCB_IGNORE_ONE_SIGSTOP;
+				tcp->flags |= TCB_ATTACHED | TCB_STARTUP | post_attach_sigstop;
 				if (!qflag)
 					fprintf(stderr, "Process %d attached\n",
 						pid);
@@ -2540,8 +2636,12 @@ trace()
 		}
 
 		if (sig != syscall_trap_sig) {
+			siginfo_t si;
+			int stopped;
+
 			if (sig == SIGSTOP &&
 					(tcp->flags & TCB_SIGTRAPPED)) {
+//TODO: testcase.
 				/*
 				 * Trapped attempt to block SIGTRAP
 				 * Hope we are back in control now.
@@ -2549,9 +2649,14 @@ trace()
 				tcp->flags &= ~(TCB_INSYSCALL | TCB_SIGTRAPPED);
 				goto restart_tracee_with_sig_0;
 			}
+
+			/* Nonzero (true) if tracee is stopped by signal
+			 * (as opposed to "tracee received signal").
+			 */
+			stopped = ptrace(PTRACE_GETSIGINFO, pid, 0, &si);
+
 			if (cflag != CFLAG_ONLY_STATS
 			    && (qual_flags[sig] & QUAL_SIGNAL)) {
-				siginfo_t si;
 #if defined(PT_CR_IPSR) && defined(PT_CR_IIP)
 				long pc = 0;
 				long psr = 0;
@@ -2568,7 +2673,7 @@ trace()
 # define PC_FORMAT_ARG	/* nothing */
 #endif
 				printleader(tcp);
-				if (ptrace(PTRACE_GETSIGINFO, pid, 0, &si) == 0) {
+				if (!stopped) {
 					tprints("--- ");
 					printsiginfo(&si, verbose(tcp));
 					tprintf(" (%s)" PC_FORMAT_STR " ---",
@@ -2581,6 +2686,26 @@ trace()
 						PC_FORMAT_ARG);
 				printtrailer();
 			}
+			if (!stopped)
+				/* It's signal-delivery-stop. Inject the signal */
+				goto restart_tracee;
+
+			/* It's group-stop */
+#ifdef USE_SEIZE
+			if (use_seize) {
+				/*
+				 * This ends ptrace-stop, but does *not* end group-stop.
+				 * This makes stopping signals work properly on straced process
+				 * (that is, process really stops. It used to continue to run).
+				 */
+				if (ptrace_restart(PTRACE_LISTEN, tcp, 0) < 0) {
+					cleanup();
+					return -1;
+				}
+				continue;
+			}
+			/* We don't have PTRACE_LISTEN support... */
+#endif
 			goto restart_tracee;
 		}
 
diff -d -urpN strace.4/util.c strace.5/util.c
--- strace.4/util.c	2011-09-02 11:42:19.753317922 +0200
+++ strace.5/util.c	2011-09-02 11:42:25.706451203 +0200
@@ -224,6 +224,10 @@ ptrace_restart(int op, struct tcb *tcp, 
 		msg = "CONT";
 	if (op == PTRACE_DETACH)
 		msg = "DETACH";
+#ifdef PTRACE_LISTEN
+	if (op == PTRACE_LISTEN)
+		msg = "LISTEN";
+#endif
 	perror_msg("ptrace(PTRACE_%s,1,%d)", msg, sig);
 	return -1;
 }






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