[PATCH/v2 1/2] Test how PTRACE_SETOPTIONS support works

[Wang Chao]

Currently only test fork related options. Fork a child that uses
PTRACE_TRACEME at startup and then does a fork so strace can test
how the PTRACE_SETOPTIONS support works before it handles any real
tracee. Since PTRACE_O_TRACECLONE/*FORK were introduced to kernel
at the same time, so this test seems enough for these 3 options.

* defs.h [LINUX]: Define PTRACE_O_TRACECLONE et al macros here;
  Variable declaration.
* strace.c [LINUX](test_ptrace_setoptions): New function for testing
  whether kernel supports PTRACE_O_CLONE/*FORK, the result is stored
  in the new variable for later use.
  (main): Call that function if followfork option is set.

Signed-off-by: Wang Chao <wang.chao at cn.fujitsu.com>
---
 defs.h   |   26 ++++++++++++++++++++
 strace.c |   81 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 107 insertions(+), 0 deletions(-)

diff --git a/defs.h b/defs.h
index fc7e362..eee4710 100644
--- a/defs.h
+++ b/defs.h
@@ -308,6 +308,31 @@ extern int mp_ioctl (int f, int c, void *a, int s);
 #define PR_FAULTED      S_CORE
 #endif
 
+#ifdef LINUX
+# ifndef PTRACE_SETOPTIONS
+#  define PTRACE_SETOPTIONS	0x4200
+# endif
+# ifndef PTRACE_O_TRACEFORK
+#  define PTRACE_O_TRACEFORK	0x00000002
+# endif
+# ifndef PTRACE_O_TRACEVFORK
+#  define PTRACE_O_TRACEVFORK	0x00000004
+# endif
+# ifndef PTRACE_O_TRACECLONE
+#  define PTRACE_O_TRACECLONE	0x00000008
+# endif
+
+# ifndef PTRACE_EVENT_FORK
+#  define PTRACE_EVENT_FORK	1
+# endif
+# ifndef PTRACE_EVENT_VFORK
+#  define PTRACE_EVENT_VFORK	2
+# endif
+# ifndef PTRACE_EVENT_CLONE
+#  define PTRACE_EVENT_CLONE	3
+# endif
+#endif /* LINUX */
+
 /* Trace Control Block */
 struct tcb {
 	short flags;		/* See below for TCB_ values */
@@ -470,6 +495,7 @@ typedef enum {
 extern struct tcb **tcbtab;
 extern int *qual_flags;
 extern int debug, followfork;
+extern unsigned int ptrace_setoptions;
 extern int dtime, xflag, qflag;
 extern cflag_t cflag;
 extern int acolumn;
diff --git a/strace.c b/strace.c
index 497b8d1..09aedac 100644
--- a/strace.c
+++ b/strace.c
@@ -83,6 +83,7 @@ extern char *optarg;
 
 
 int debug = 0, followfork = 0;
+unsigned int ptrace_setoptions = 0;
 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;
@@ -686,6 +687,77 @@ startup_child (char **argv)
 #endif /* USE_PROCFS */
 }
 
+#ifdef LINUX
+/*
+ * Test whether kernel support PTRACE_O_TRACECLONE et al options.
+ * First fork a new child, call ptrace with PTRACE_SETOPTIONS on it,
+ * and then see which options are supported on this kernel.
+ */
+static int
+test_ptrace_setoptions(void)
+{
+	int pid;
+
+	if ((pid = fork()) < 0)
+		return -1;
+	else if (pid == 0) {
+		if (ptrace(PTRACE_TRACEME, 0, (char *)1, 0) < 0) {
+			_exit(1);
+		}
+		kill(getpid(), SIGSTOP);
+		if ((pid = fork()) < 0) {
+			_exit(1);
+		}
+		_exit(0);
+	}
+	else {
+		int status, tracee_pid, error;
+		int no_child = 0;
+		while (1) {
+			tracee_pid = wait4(-1, &status, 0, NULL);
+			error = errno;
+			if (tracee_pid == -1) {
+				switch (error) {
+				case EINTR:
+					continue;
+				case ECHILD:
+					no_child = 1;
+					break;
+				default:
+					errno = error;
+					perror("test_ptrace_setoptions");
+					return -1;
+				}
+			}
+			if (no_child)
+				break;
+			if (tracee_pid != pid) {
+				if (ptrace(PTRACE_CONT, tracee_pid, 0, 0) < 0 &&
+				    errno != ESRCH)
+					kill(tracee_pid, SIGKILL);
+			}
+			else if (WIFSTOPPED(status)) {
+				if (status >> 16 == PTRACE_EVENT_FORK)
+					ptrace_setoptions |= (PTRACE_O_TRACEVFORK |
+							      PTRACE_O_TRACECLONE |
+							      PTRACE_O_TRACEFORK);
+				if (WSTOPSIG(status) == SIGSTOP) {
+					if (ptrace(PTRACE_SETOPTIONS, pid, NULL,
+						   PTRACE_O_TRACEFORK) < 0) {
+						kill(pid, SIGKILL);
+						return -1;
+					}
+				}
+				if (ptrace(PTRACE_SYSCALL, pid, 0, 0) < 0 &&
+				    errno != ESRCH)
+					kill(pid, SIGKILL);
+			}
+		}
+	}
+	return 0;
+}
+#endif
+
 int
 main(int argc, char *argv[])
 {
@@ -914,6 +986,15 @@ main(int argc, char *argv[])
 		interactive = 0;
 		qflag = 1;
 	}
+
+#ifdef LINUX
+	if (followfork && test_ptrace_setoptions() < 0) {
+		fprintf(stderr, "Test for options supported by PTRACE_SETOPTIONS\
+			failed, give up using this feature\n");
+		ptrace_setoptions = 0;
+	}
+#endif
+
 	/* Valid states here:
 	   optind < argc	pflag_seen	outfname	interactive
 	   1			0		0		1
-- 
1.6.5.2