From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 27809 invoked by alias); 13 Nov 2004 22:25:16 -0000 Mailing-List: contact gdb-patches-help@sources.redhat.com; run by ezmlm Precedence: bulk List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sources.redhat.com Received: (qmail 27718 invoked from network); 13 Nov 2004 22:25:10 -0000 Received: from unknown (HELO nevyn.them.org) (66.93.172.17) by sourceware.org with SMTP; 13 Nov 2004 22:25:10 -0000 Received: from drow by nevyn.them.org with local (Exim 4.34 #1 (Debian)) id 1CT6KQ-0008Of-HZ for ; Sat, 13 Nov 2004 17:25:06 -0500 Date: Sat, 13 Nov 2004 22:25:00 -0000 From: Daniel Jacobowitz To: gdb-patches@sources.redhat.com Subject: Re: [rfc] Fix linux_test_for_tracefork for newer kernels Message-ID: <20041113222506.GA32180@nevyn.them.org> Mail-Followup-To: gdb-patches@sources.redhat.com References: <20041112225940.GA15711@nevyn.them.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20041112225940.GA15711@nevyn.them.org> User-Agent: Mutt/1.5.5.1+cvs20040105i X-SW-Source: 2004-11/txt/msg00291.txt.bz2 On Fri, Nov 12, 2004 at 05:59:41PM -0500, Daniel Jacobowitz wrote: > This patch makes the run-time test for fork tracing a little more robust. > In particular, it fixes two things: > - If the test failed in an unexpected way, then two stopped processes > could be left around. > - Waitpid can be interrupted by EINTR. Kernel 2.6.10-rc1 has some > changes to wait and signal processing, which cause the SIGCHLD > to be received before wait returns. I don't think there's any > actual bug here, since reissuing the wait works fine. > > These changes let my testsuite runs finish without leaving hordes of stopped > processes around. I won't check it in yet, since I haven't tested it on a > system where this runtime check should fail; in the meantime, I'm just > posting it for comments. Hopefully I got it right this time! Now I've tested it in a couple of other systems. Here's a revised version, with a spurious warning fixed, and one additional improvement: on most systems lacking the support, we don't need to fork for the runtime test. This fixes some problems in user-mode-linux, which does the most disgusting things with ptrace I have ever encountered. Wow! Barring comments, I'll check this in in a few days. -- Daniel Jacobowitz 2004-11-12 Daniel Jacobowitz * 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;