--- /dev/null
+Status: submitted for comments
+
+2004-11-12 Daniel Jacobowitz <dan@debian.org>
+
+ * linux-nat.c (my_waitpid): New function.
+ (linux_test_for_tracefork): Make more robust and verbose. Take
+ an ORIGINAL_PID argument and test for PTRACE_SETOPTIONS first.
+ (linux_supports_tracefork, linux_supports_tracevforkdone): Take a PID
+ argument. Update calls to linux_test_for_tracefork.
+ (linux_enable_event_reporting, child_follow_fork)
+ (child_insert_fork_catchpoint, child_insert_vfork_catchpoint)
+ (child_insert_exec_catchpoint): Update calls to
+ linux_supports_tracefork and linux_supports_tracevforkdone.
+
+Index: gdb-6.3/gdb/linux-nat.c
+===================================================================
+--- gdb-6.3.orig/gdb/linux-nat.c 2004-10-08 16:29:47.000000000 -0400
++++ gdb-6.3/gdb/linux-nat.c 2004-11-13 16:41:51.368720845 -0500
+@@ -150,18 +150,47 @@ linux_tracefork_child (void)
+ exit (0);
+ }
+
+-/* Determine if PTRACE_O_TRACEFORK can be used to follow fork events. We
++/* Wrapper function for waitpid which handles EINTR. */
++
++static int
++my_waitpid (int pid, int *status, int flags)
++{
++ int ret;
++ do
++ {
++ ret = waitpid (pid, status, flags);
++ }
++ while (ret == -1 && errno == EINTR);
++
++ return ret;
++}
++
++/* Determine if PTRACE_O_TRACEFORK can be used to follow fork events.
++
++ First, we try to enable fork tracing on ORIGINAL_PID. If this fails,
++ we know that the feature is not available. This may change the tracing
++ options for ORIGINAL_PID, but we'll be setting them shortly anyway.
++
++ However, if it succeeds, we don't know for sure that the feature is
++ available; old versions of PTRACE_SETOPTIONS ignored unknown options. We
+ create a child process, attach to it, use PTRACE_SETOPTIONS to enable
+- fork tracing, and let it fork. If the process exits, we assume that
+- we can't use TRACEFORK; if we get the fork notification, and we can
+- extract the new child's PID, then we assume that we can. */
++ fork tracing, and let it fork. If the process exits, we assume that we
++ can't use TRACEFORK; if we get the fork notification, and we can extract
++ the new child's PID, then we assume that we can. */
+
+ static void
+-linux_test_for_tracefork (void)
++linux_test_for_tracefork (int original_pid)
+ {
+ int child_pid, ret, status;
+ long second_pid;
+
++ linux_supports_tracefork_flag = 0;
++ linux_supports_tracevforkdone_flag = 0;
++
++ ret = ptrace (PTRACE_SETOPTIONS, original_pid, 0, PTRACE_O_TRACEFORK);
++ if (ret != 0)
++ return;
++
+ child_pid = fork ();
+ if (child_pid == -1)
+ perror_with_name ("linux_test_for_tracefork: fork");
+@@ -169,7 +198,7 @@ linux_test_for_tracefork (void)
+ if (child_pid == 0)
+ linux_tracefork_child ();
+
+- ret = waitpid (child_pid, &status, 0);
++ ret = my_waitpid (child_pid, &status, 0);
+ if (ret == -1)
+ perror_with_name ("linux_test_for_tracefork: waitpid");
+ else if (ret != child_pid)
+@@ -177,13 +206,23 @@ linux_test_for_tracefork (void)
+ if (! WIFSTOPPED (status))
+ error ("linux_test_for_tracefork: waitpid: unexpected status %d.", status);
+
+- linux_supports_tracefork_flag = 0;
+-
+ ret = ptrace (PTRACE_SETOPTIONS, child_pid, 0, PTRACE_O_TRACEFORK);
+ if (ret != 0)
+ {
+- ptrace (PTRACE_KILL, child_pid, 0, 0);
+- waitpid (child_pid, &status, 0);
++ ret = ptrace (PTRACE_KILL, child_pid, 0, 0);
++ if (ret != 0)
++ {
++ warning ("linux_test_for_tracefork: failed to kill child");
++ return;
++ }
++
++ ret = my_waitpid (child_pid, &status, 0);
++ if (ret != child_pid)
++ warning ("linux_test_for_tracefork: failed to wait for killed child");
++ else if (!WIFSIGNALED (status))
++ warning ("linux_test_for_tracefork: unexpected wait status 0x%x from "
++ "killed child", status);
++
+ return;
+ }
+
+@@ -192,8 +231,12 @@ linux_test_for_tracefork (void)
+ PTRACE_O_TRACEFORK | PTRACE_O_TRACEVFORKDONE);
+ linux_supports_tracevforkdone_flag = (ret == 0);
+
+- ptrace (PTRACE_CONT, child_pid, 0, 0);
+- ret = waitpid (child_pid, &status, 0);
++ ret = ptrace (PTRACE_CONT, child_pid, 0, 0);
++ if (ret != 0)
++ warning ("linux_test_for_tracefork: failed to resume child");
++
++ ret = my_waitpid (child_pid, &status, 0);
++
+ if (ret == child_pid && WIFSTOPPED (status)
+ && status >> 16 == PTRACE_EVENT_FORK)
+ {
+@@ -204,34 +247,38 @@ linux_test_for_tracefork (void)
+ int second_status;
+
+ linux_supports_tracefork_flag = 1;
+- waitpid (second_pid, &second_status, 0);
+- ptrace (PTRACE_DETACH, second_pid, 0, 0);
++ my_waitpid (second_pid, &second_status, 0);
++ ret = ptrace (PTRACE_KILL, second_pid, 0, 0);
++ if (ret != 0)
++ warning ("linux_test_for_tracefork: failed to kill second child");
+ }
+ }
++ else
++ warning ("linux_test_for_tracefork: unexpected result from waitpid "
++ "(%d, status 0x%x)", ret, status);
+
+- if (WIFSTOPPED (status))
+- {
+- ptrace (PTRACE_DETACH, child_pid, 0, 0);
+- waitpid (child_pid, &status, 0);
+- }
++ ret = ptrace (PTRACE_KILL, child_pid, 0, 0);
++ if (ret != 0)
++ warning ("linux_test_for_tracefork: failed to kill child");
++ my_waitpid (child_pid, &status, 0);
+ }
+
+ /* Return non-zero iff we have tracefork functionality available.
+ This function also sets linux_supports_tracefork_flag. */
+
+ static int
+-linux_supports_tracefork (void)
++linux_supports_tracefork (int pid)
+ {
+ if (linux_supports_tracefork_flag == -1)
+- linux_test_for_tracefork ();
++ linux_test_for_tracefork (pid);
+ return linux_supports_tracefork_flag;
+ }
+
+ static int
+-linux_supports_tracevforkdone (void)
++linux_supports_tracevforkdone (int pid)
+ {
+ if (linux_supports_tracefork_flag == -1)
+- linux_test_for_tracefork ();
++ linux_test_for_tracefork (pid);
+ return linux_supports_tracevforkdone_flag;
+ }
+
+@@ -242,12 +289,12 @@ linux_enable_event_reporting (ptid_t pti
+ int pid = ptid_get_pid (ptid);
+ int options;
+
+- if (! linux_supports_tracefork ())
++ if (! linux_supports_tracefork (pid))
+ return;
+
+ options = PTRACE_O_TRACEFORK | PTRACE_O_TRACEVFORK | PTRACE_O_TRACEEXEC
+ | PTRACE_O_TRACECLONE;
+- if (linux_supports_tracevforkdone ())
++ if (linux_supports_tracevforkdone (pid))
+ options |= PTRACE_O_TRACEVFORKDONE;
+
+ /* Do not enable PTRACE_O_TRACEEXIT until GDB is more prepared to support
+@@ -308,7 +355,8 @@ child_follow_fork (int follow_child)
+
+ if (has_vforked)
+ {
+- if (linux_supports_tracevforkdone ())
++ gdb_assert (linux_supports_tracefork_flag >= 0);
++ if (linux_supports_tracevforkdone (0))
+ {
+ int status;
+
+@@ -476,7 +524,7 @@ linux_handle_extended_wait (int pid, int
+ int
+ child_insert_fork_catchpoint (int pid)
+ {
+- if (! linux_supports_tracefork ())
++ if (! linux_supports_tracefork (pid))
+ error ("Your system does not support fork catchpoints.");
+
+ return 0;
+@@ -485,7 +533,7 @@ child_insert_fork_catchpoint (int pid)
+ int
+ child_insert_vfork_catchpoint (int pid)
+ {
+- if (!linux_supports_tracefork ())
++ if (!linux_supports_tracefork (pid))
+ error ("Your system does not support vfork catchpoints.");
+
+ return 0;
+@@ -494,7 +542,7 @@ child_insert_vfork_catchpoint (int pid)
+ int
+ child_insert_exec_catchpoint (int pid)
+ {
+- if (!linux_supports_tracefork ())
++ if (!linux_supports_tracefork (pid))
+ error ("Your system does not support exec catchpoints.");
+
+ return 0;
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