http://sourceware.org/ml/gdb-patches/2012-03/msg00170.html Subject: [patch 2/3] attach-fail-reasons: Say more than ptrace: Operation not permitted. Hi, There is a common question on #gdb and also already described: http://sourceware.org/gdb/wiki/FAQ 16. Getting an internal error or other error while attaching to processes on GNU/Linux -> Try setenforce 0 (SELinux) or echo 0 >/proc/sys/kernel/yama/ptrace_scope (ptrace scope) to disable system security protections. and here is a patch to give some explanations. More reasons can be given later, this is a container for them and it contains some useful ones already. No regressions on {x86_64,x86_64-m32,i686}-fedora17-linux-gnu and with non-extended gdbserver. The testcase does not test gdbserver, somehow it is a bit difficult without having shell on target. Attaching to process 27480 ptrace: Operation not permitted. (gdb) _ -> Attaching to process 27480 warning: process 27480 is already traced by process 29011 ptrace: Operation not permitted. (gdb) _ Thanks, Jan gdb/ 2012-03-06 Jan Kratochvil * common/linux-procfs.c (linux_proc_get_int): New, from linux_proc_get_tgid. (linux_proc_get_tgid): Only call linux_proc_get_int. (linux_proc_get_tracerpid): New. (linux_proc_pid_has_state): New, from linux_proc_pid_is_zombie. (linux_proc_pid_is_stopped, linux_proc_pid_is_zombie): Only call linux_proc_pid_has_state. * common/linux-procfs.h (linux_proc_get_tracerpid): New declaration. * common/linux-ptrace.c: Include linux-procfs.h. (linux_ptrace_attach_warnings): New. * common/linux-ptrace.h (linux_ptrace_attach_warnings): New declaration. * linux-nat.c: Include exceptions.h and linux-ptrace.h. (linux_nat_attach): New variable ex. Wrap to_attach by TRY_CATCH and call linux_ptrace_attach_warnings. gdb/gdbserver/ 2012-03-06 Jan Kratochvil * linux-low.c (linux_attach_lwp_1): Call linux_ptrace_attach_warnings. gdb/testsuite/ 2012-03-06 Jan Kratochvil * gdb.base/attach-twice.c: New files. * gdb.base/attach-twice.exp: New files. Index: gdb-7.4.50.20120120/gdb/common/linux-procfs.c =================================================================== --- gdb-7.4.50.20120120.orig/gdb/common/linux-procfs.c 2012-03-06 07:34:00.000000000 +0100 +++ gdb-7.4.50.20120120/gdb/common/linux-procfs.c 2012-03-06 07:34:17.586816449 +0100 @@ -28,67 +28,54 @@ /* Return the TGID of LWPID from /proc/pid/status. Returns -1 if not found. */ -int -linux_proc_get_tgid (int lwpid) +static int +linux_proc_get_int (int lwpid, const char *field) { + size_t field_len = strlen (field); FILE *status_file; char buf[100]; - int tgid = -1; + int retval = -1; snprintf (buf, sizeof (buf), "/proc/%d/status", (int) lwpid); status_file = fopen (buf, "r"); - if (status_file != NULL) + if (status_file == NULL) { - while (fgets (buf, sizeof (buf), status_file)) - { - if (strncmp (buf, "Tgid:", 5) == 0) - { - tgid = strtoul (buf + strlen ("Tgid:"), NULL, 10); - break; - } - } - - fclose (status_file); + warning (_("unable to open /proc file '%s'"), buf); + return -1; } - return tgid; + while (fgets (buf, sizeof (buf), status_file)) + if (strncmp (buf, field, field_len) == 0 && buf[field_len] == ':') + { + retval = strtol (&buf[field_len + 1], NULL, 10); + break; + } + + fclose (status_file); + return retval; } -/* Detect `T (stopped)' in `/proc/PID/status'. - Other states including `T (tracing stop)' are reported as false. */ +/* Return the TGID of LWPID from /proc/pid/status. Returns -1 if not + found. */ int -linux_proc_pid_is_stopped (pid_t pid) +linux_proc_get_tgid (int lwpid) { - FILE *status_file; - char buf[100]; - int retval = 0; + return linux_proc_get_int (lwpid, "Tgid"); +} - snprintf (buf, sizeof (buf), "/proc/%d/status", (int) pid); - status_file = fopen (buf, "r"); - if (status_file != NULL) - { - int have_state = 0; +/* See linux-procfs.h. */ - while (fgets (buf, sizeof (buf), status_file)) - { - if (strncmp (buf, "State:", 6) == 0) - { - have_state = 1; - break; - } - } - if (have_state && strstr (buf, "T (stopped)") != NULL) - retval = 1; - fclose (status_file); - } - return retval; +pid_t +linux_proc_get_tracerpid (int lwpid) +{ + return linux_proc_get_int (lwpid, "TracerPid"); } -/* See linux-procfs.h declaration. */ +/* Return non-zero if 'State' of /proc/PID/status contains STATE. */ -int -linux_proc_pid_is_zombie (pid_t pid) +static int +linux_proc_pid_has_state (pid_t pid, const char *state) { char buffer[100]; FILE *procfile; @@ -110,8 +97,24 @@ linux_proc_pid_is_zombie (pid_t pid) have_state = 1; break; } - retval = (have_state - && strcmp (buffer, "State:\tZ (zombie)\n") == 0); + retval = (have_state && strstr (buffer, state) != NULL); fclose (procfile); return retval; } + +/* Detect `T (stopped)' in `/proc/PID/status'. + Other states including `T (tracing stop)' are reported as false. */ + +int +linux_proc_pid_is_stopped (pid_t pid) +{ + return linux_proc_pid_has_state (pid, "T (stopped)"); +} + +/* See linux-procfs.h declaration. */ + +int +linux_proc_pid_is_zombie (pid_t pid) +{ + return linux_proc_pid_has_state (pid, "Z (zombie)"); +} Index: gdb-7.4.50.20120120/gdb/common/linux-procfs.h =================================================================== --- gdb-7.4.50.20120120.orig/gdb/common/linux-procfs.h 2012-03-06 07:34:00.000000000 +0100 +++ gdb-7.4.50.20120120/gdb/common/linux-procfs.h 2012-03-06 07:34:17.586816449 +0100 @@ -26,6 +26,11 @@ extern int linux_proc_get_tgid (int lwpid); +/* Return the TracerPid of LWPID from /proc/pid/status. Returns -1 if not + found. */ + +extern pid_t linux_proc_get_tracerpid (int lwpid); + /* Detect `T (stopped)' in `/proc/PID/status'. Other states including `T (tracing stop)' are reported as false. */ Index: gdb-7.4.50.20120120/gdb/common/linux-ptrace.c =================================================================== --- gdb-7.4.50.20120120.orig/gdb/common/linux-ptrace.c 2012-03-06 07:34:00.000000000 +0100 +++ gdb-7.4.50.20120120/gdb/common/linux-ptrace.c 2012-03-06 07:34:17.586816449 +0100 @@ -24,3 +24,21 @@ #endif #include "linux-ptrace.h" +#include "linux-procfs.h" + +/* Print all possible reasons we could fail to attach PID. */ + +void +linux_ptrace_attach_warnings (pid_t pid) +{ + pid_t tracerpid; + + tracerpid = linux_proc_get_tracerpid (pid); + if (tracerpid > 0) + warning (_("process %d is already traced by process %d"), (int) pid, + (int) tracerpid); + + if (linux_proc_pid_is_zombie (pid)) + warning (_("process %d is a zombie - the process has already terminated"), + (int) pid); +} Index: gdb-7.4.50.20120120/gdb/common/linux-ptrace.h =================================================================== --- gdb-7.4.50.20120120.orig/gdb/common/linux-ptrace.h 2012-01-04 09:17:18.000000000 +0100 +++ gdb-7.4.50.20120120/gdb/common/linux-ptrace.h 2012-03-06 07:34:17.586816449 +0100 @@ -65,4 +65,6 @@ #define __WALL 0x40000000 /* Wait for any child. */ #endif +extern void linux_ptrace_attach_warnings (pid_t pid); + #endif /* COMMON_LINUX_PTRACE_H */ Index: gdb-7.4.50.20120120/gdb/gdbserver/linux-low.c =================================================================== --- gdb-7.4.50.20120120.orig/gdb/gdbserver/linux-low.c 2012-03-06 07:34:00.000000000 +0100 +++ gdb-7.4.50.20120120/gdb/gdbserver/linux-low.c 2012-03-06 07:34:17.587816446 +0100 @@ -632,6 +632,7 @@ linux_attach_lwp_1 (unsigned long lwpid, } /* If we fail to attach to a process, report an error. */ + linux_ptrace_attach_warnings (lwpid); error ("Cannot attach to lwp %ld: %s (%d)\n", lwpid, strerror (errno), errno); } Index: gdb-7.4.50.20120120/gdb/linux-nat.c =================================================================== --- gdb-7.4.50.20120120.orig/gdb/linux-nat.c 2012-03-06 07:34:00.000000000 +0100 +++ gdb-7.4.50.20120120/gdb/linux-nat.c 2012-03-06 07:34:29.860775803 +0100 @@ -59,6 +59,8 @@ #include "solib.h" #include "linux-osdata.h" #include "cli/cli-utils.h" +#include "exceptions.h" +#include "linux-ptrace.h" #ifndef SPUFS_MAGIC #define SPUFS_MAGIC 0x23c9b64e @@ -1613,11 +1615,22 @@ linux_nat_attach (struct target_ops *ops struct lwp_info *lp; int status; ptid_t ptid; + volatile struct gdb_exception ex; /* Make sure we report all signals during attach. */ linux_nat_pass_signals (0, NULL); - linux_ops->to_attach (ops, args, from_tty); + TRY_CATCH (ex, RETURN_MASK_ERROR) + { + linux_ops->to_attach (ops, args, from_tty); + } + if (ex.reason < 0) + { + pid_t pid = parse_pid_to_attach (args); + + linux_ptrace_attach_warnings (pid); + throw_exception (ex); + } /* The ptrace base target adds the main thread with (pid,0,0) format. Decorate it with lwp info. */ Index: gdb-7.4.50.20120120/gdb/testsuite/gdb.base/attach-twice.c =================================================================== --- /dev/null 1970-01-01 00:00:00.000000000 +0000 +++ gdb-7.4.50.20120120/gdb/testsuite/gdb.base/attach-twice.c 2012-03-06 07:34:17.589816440 +0100 @@ -0,0 +1,42 @@ +/* This testcase is part of GDB, the GNU debugger. + + Copyright 2011-2012 Free Software Foundation, Inc. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see . */ + +#include +#include +#include +#include + +int +main (void) +{ + long l; + + switch (fork ()) + { + case -1: + perror ("fork"); + exit (1); + case 0: + errno = 0; + ptrace (PTRACE_ATTACH, getppid (), NULL, NULL); + if (errno != 0) + perror ("PTRACE_ATTACH"); + break; + } + sleep (600); + return 0; +} Index: gdb-7.4.50.20120120/gdb/testsuite/gdb.base/attach-twice.exp =================================================================== --- /dev/null 1970-01-01 00:00:00.000000000 +0000 +++ gdb-7.4.50.20120120/gdb/testsuite/gdb.base/attach-twice.exp 2012-03-06 07:34:17.589816440 +0100 @@ -0,0 +1,52 @@ +# Copyright (C) 2012 Free Software Foundation, Inc. +# +# This program is free software; you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation; either version 3 of the License, or +# (at your option) any later version. +# +# This program is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. +# +# You should have received a copy of the GNU General Public License +# along with this program. If not, see . + +# Manipulation with PID on target is not supported. +if [is_remote target] then { + return 0 +} + +set testfile attach-twice +set executable ${testfile} +set binfile ${objdir}/${subdir}/${executable} + +if { [prepare_for_testing ${testfile}.exp $executable] } { + return -1 +} + +set testpid [eval exec $binfile &] +exec sleep 2 + +set parentpid 0 + +set test "attach" +gdb_test_multiple "attach $testpid" $test { + -re "Attaching to program: \[^\r\n\]*, process $testpid\r\n.*warning: process $testpid is already traced by process (\[0-9\]+)\r\n.*ptrace: Operation not permitted\\.\r\n$gdb_prompt $" { + set parentpid $expect_out(1,string) + pass $test + } + -re "Attaching to program: \[^\r\n\]*, process $testpid\r\n.*ptrace: Operation not permitted\\.\r\n$gdb_prompt $" { + fail $test + } + -re "\r\n$gdb_prompt $" { + xfail $test + } +} + +eval exec ps xfw +if {$parentpid != 0} { + eval exec kill -9 $parentpid +} +eval exec kill -9 $testpid