Re: [PATCH v3] Fix gdbserver crash when doing ftrace commands after detach or process exit

[Antoine Tremblay <antoine dot tremblay at ericsson dot com>]

Antoine Tremblay writes:

> In this v3:
>   - Reworked the test to be more comprehensive.
>   - Removed uneeded .* before Connection timeout test  
>
> --
> This patch fixes a gdbserver crash that is triggered by the following
> sequence of events:
>
>  - A process with the in-process agent loaded is debugged under gdbserver.
>  - The process is detached or exits with or without stopping the trace before.
>  - Commands tstatus, enable/disable, ftrace, tstop, disconnect with fast
>  tracepoints are used.
>
> Using either of tstatus or enable/disable ends up sending the qtstatus
> packet to gdbserver.  During the handling of qtstatus, agent_loaded_p ()
> returns true, even though the process that once had the agent loaded is
> not present anymore.  We end up trying to read memory with
> current_thread == NULL, causing a segfault here:
>
>   gdb/gdbserver/linux-low.c:5560(linux_read_memory)[0x43583c]
>   gdb/gdbserver/target.c:153(read_inferior_memory)[0x415d78]
>   gdb/gdbserver/tracepoint.c:424(read_inferior_uinteger)[0x41c7fb]
>   gdb/gdbserver/tracepoint.c:6288(upload_fast_traceframes)[0x425558]
>   gdb/gdbserver/tracepoint.c:3645(cmd_qtstatus)[0x420dee]
>   gdb/gdbserver/tracepoint.c:4239(handle_tracepoint_query)[0x4222ab]
>   gdb/gdbserver/server.c:2543(handle_query)[0x411639]
>   gdb/gdbserver/server.c:3910(process_serial_event)[0x413f39]
>   gdb/gdbserver/server.c:4347(handle_serial_event)[0x415010]
>   gdb/gdbserver/event-loop.c:428(handle_file_event)[0x41bed7]
>   gdb/gdbserver/event-loop.c:184(process_event)[0x41b69e]
>   gdb/gdbserver/event-loop.c:547(start_event_loop)[0x41c41d]
>   gdb/gdbserver/server.c:3723(captured_main)[0x413a53]
>   gdb/gdbserver/server.c:3802(main)[0x413c2f]
>
> ftrace, tstop and quit need to be protected from current_thread == NULL in a
> similar manner.
>
> This patch adds a test called
> gdb.trace/ftrace-commands-after-detach-or-exit.exp.
>
> No regression on x86-linux { native-gdbserver , native-extended-gdbserver }
>
> gdb/gdbserver/ChangeLog:
>
> 	* tracepoint.c (cmd_qtdp): Check for current_thread == NULL.
> 	(cmd_qtenable_disable): Likewise.
> 	(cmd_qtstart): Likewise.
> 	(stop_tracing): Likewise.
> 	(cmd_qtstop): Likewise.
> 	(cmd_qtstatus): Likewise.
>
> gdb/testsuite/ChangeLog:
>
> 	* gdb.trace/ftrace-commands-after-detach-or-exit.c: New file.
> 	* gdb.trace/ftrace-commands-after-detach-or-exit.exp: New test.
> 	* lib/gdbserver-support.exp (gdb_target_cmd): Add support for connection
> 	timed out error.
> ---
>  gdb/gdbserver/tracepoint.c                         |  36 ++++-
>  .../ftrace-commands-after-detach-or-exit.c         |  25 ++++
>  .../ftrace-commands-after-detach-or-exit.exp       | 160 +++++++++++++++++++++
>  gdb/testsuite/lib/gdbserver-support.exp            |   4 +
>  4 files changed, 224 insertions(+), 1 deletion(-)
>  create mode 100644 gdb/testsuite/gdb.trace/ftrace-commands-after-detach-or-exit.c
>  create mode 100644 gdb/testsuite/gdb.trace/ftrace-commands-after-detach-or-exit.exp
>
> diff --git a/gdb/gdbserver/tracepoint.c b/gdb/gdbserver/tracepoint.c
> index c07e525..d80e0c98 100644
> --- a/gdb/gdbserver/tracepoint.c
> +++ b/gdb/gdbserver/tracepoint.c
> @@ -2488,6 +2488,13 @@ cmd_qtdp (char *own_buf)
>    char *actparm;
>    char *packet = own_buf;
>  
> +  /* Can't do this command without a pid attached.  */
> +  if (current_thread == NULL)
> +    {
> +      write_enn (packet);
> +      return;
> +    }
> +
>    packet += strlen ("QTDP:");
>  
>    /* A hyphen at the beginning marks a packet specifying actions for a
> @@ -2752,6 +2759,13 @@ cmd_qtenable_disable (char *own_buf, int enable)
>    ULONGEST num, addr;
>    struct tracepoint *tp;
>  
> +  /* Can't do this command without a pid attached.  */
> +  if (current_thread == NULL)
> +    {
> +      write_enn (packet);
> +      return;
> +    }
> +
>    packet += strlen (enable ? "QTEnable:" : "QTDisable:");
>    packet = unpack_varlen_hex (packet, &num);
>    ++packet; /* skip a colon */
> @@ -3202,6 +3216,13 @@ cmd_qtstart (char *packet)
>    struct tracepoint *tpoint, *prev_ftpoint, *prev_stpoint;
>    CORE_ADDR tpptr = 0, prev_tpptr = 0;
>  
> +  /* Can't do this command without a pid attached.  */
> +  if (current_thread == NULL)
> +    {
> +      write_enn (packet);
> +      return;
> +    }
> +
>    trace_debug ("Starting the trace");
>  
>    /* Pause all threads temporarily while we patch tracepoints.  */
> @@ -3420,6 +3441,12 @@ stop_tracing (void)
>        return;
>      }
>  
> +  if (current_thread == NULL)
> +    {
> +      trace_debug ("Current thread null, can't stop threads");
> +      return;
> +    }
> +
>    trace_debug ("Stopping the trace");
>  
>    /* Pause all threads before removing fast jumps from memory,
> @@ -3532,6 +3559,13 @@ flush_trace_buffer_handler (CORE_ADDR addr)
>  static void
>  cmd_qtstop (char *packet)
>  {
> +  /* Can't do this command without a pid attached.  */
> +  if (current_thread == NULL)
> +    {
> +      write_enn (packet);
> +      return;
> +    }
> +
>    stop_tracing ();
>    write_ok (packet);
>  }
> @@ -3650,7 +3684,7 @@ cmd_qtstatus (char *packet)
>    trace_debug ("Returning trace status as %d, stop reason %s",
>  	       tracing, tracing_stop_reason);
>  
> -  if (agent_loaded_p ())
> +  if (current_thread != NULL && agent_loaded_p ())
>      {
>        pause_all (1);
>  
> diff --git a/gdb/testsuite/gdb.trace/ftrace-commands-after-detach-or-exit.c b/gdb/testsuite/gdb.trace/ftrace-commands-after-detach-or-exit.c
> new file mode 100644
> index 0000000..9f93b9b
> --- /dev/null
> +++ b/gdb/testsuite/gdb.trace/ftrace-commands-after-detach-or-exit.c
> @@ -0,0 +1,25 @@
> +/* This testcase is part of GDB, the GNU debugger.
> +
> +   Copyright 2016 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 <http://www.gnu.org/licenses/>.  */
> +
> +#include "trace-common.h"
> +
> +int
> +main (void)
> +{
> +  FAST_TRACEPOINT_LABEL(set_point);
> +  return 0;
> +}
> diff --git a/gdb/testsuite/gdb.trace/ftrace-commands-after-detach-or-exit.exp b/gdb/testsuite/gdb.trace/ftrace-commands-after-detach-or-exit.exp
> new file mode 100644
> index 0000000..2034cf5
> --- /dev/null
> +++ b/gdb/testsuite/gdb.trace/ftrace-commands-after-detach-or-exit.exp
> @@ -0,0 +1,160 @@
> +# Copyright 2016 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 <http://www.gnu.org/licenses/>.
> +
> +# This test verifies that GDBServer does not crash with the following
> +# commands: tstatus, enable, disable, ftrace, tstop after a detach or run
> +# to end whether we stopped the trace before doing detach or run to end
> +# or not.
> +# This test also verifies that GDBServer does not crash on disconnect.
> +
> +load_lib "trace-support.exp"
> +
> +standard_testfile
> +set executable $testfile
> +set expfile $testfile.exp
> +
> +# Some targets have leading underscores on assembly symbols.
> +set options [list debug [gdb_target_symbol_prefix_flags]]
> +
> +# Check that the target supports trace.
> +if { [gdb_compile "$srcdir/$subdir/$srcfile" $binfile executable $options] != "" } {
> +    untested "Couldn't compile test program"
> +    return -1
> +}
> +
> +clean_restart ${testfile}
> +
> +if ![runto_main] {
> +    fail "Can't run to main to check for trace support"
> +    return -1
> +}
> +
> +if $use_gdb_stub {
> +    # This test is about testing commands after detaching from a process or
> +    # after letting a process exit, so it doesn't make sense to run it if the
> +    # target is stub-like.
> +    unsupported "This test is not supported for GDB stub targets."
> +    return -1
> +}
> +
> +if ![gdb_target_supports_trace] {
> +    unsupported "target does not support trace"
> +    return -1
> +}
> +
> +# Compile the test case with the in-process agent library.
> +set libipa [get_in_proc_agent]
> +set remote_libipa [gdb_load_shlib $libipa]
> +
> +lappend options shlib=$libipa
> +
> +if { [gdb_compile "$srcdir/$subdir/$srcfile" $binfile executable $options] != "" } {
> +    untested "Couldn't compile test program with in-process agent library"
> +    return -1
> +}
> +
> +clean_restart ${testfile}
> +
> +if ![runto_main] {
> +    fail "Can't run to main to check for trace support"
> +    return -1
> +}
> +
> +if { [gdb_test "info sharedlibrary" ".*${remote_libipa}.*" "IPA loaded"] != 0 } {
> +    untested "Could not find IPA lib loaded"
> +    return -1
> +}
> +
> +proc do_test {command detach_method tstop} {
> +    global executable binfile decimal gdbserver_reconnect_p
> +    set gdbserver_reconnect_p 1
> +    clean_restart ${executable}
> +
> +    if ![runto_main] {
> +	fail "Can't run to main."
> +	return -1
> +    }
> +
> +    gdb_test_no_output "set confirm off"
> +    gdb_test "ftrace set_point" "Fast tracepoint .*"
> +    gdb_test_no_output "tstart"
> +
> +    if {$tstop} {
> +	gdb_test_no_output "tstop"
> +    }
> +
> +    if {$detach_method == "detach"} {
> +	gdb_test "detach" "Detaching from program: $binfile, process $decimal"
> +    } elseif {$detach_method == "exit"} {
> +	gdb_continue_to_end
> +    }
> +
> +    switch $command {
> +	"tstatus" {
> +	    if {$detach_method == "exit" && $tstop == 0} {
> +		gdb_test "tstatus" "Trace is running on the target\..*"
> +	    } else {
> +		gdb_test "tstatus" "Trace stopped by a tstop command ()\..*"
> +	    }
> +	}
> +	"disable" {
> +	    if {!$tstop} {
> +		gdb_test "$command" "Target returns error code \'01\'\."
> +	    } else {
> +		gdb_test_no_output "$command"
> +	    }
> +	}
> +	"enable" {
> +	    if {!$tstop && $detach_method == "exit"} {
> +		gdb_test "$command" "Target returns error code \'01\'\."
> +	    } else {
> +		gdb_test_no_output "$command"
> +	    }
> +	}
> +	"ftrace" {
> +	    gdb_test "ftrace set_point" ".*Fast tracepoint \[0-9]+ at.*"
> +	}
> +	"tstop" {
> +	    gdb_test "tstop" "Target returns error code \'01\'\."
> +	}
> +    }
> +
> +    test_gdbserver_still_alive
> +}
> +
> +# Test if gdbserver is still alive by reconnecting to it.
> +proc test_gdbserver_still_alive { } {
> +    gdb_test "disconnect" "Ending remote debugging\\."
> +    set test "reconnect to GDBserver"
> +    if { [gdb_reconnect] == 0 } {
> +	pass $test
> +    } else {
> +	fail $test
> +	return 0
> +    }
> +}
> +
> +
> +foreach command {"tstatus" "disable" "enable" "ftrace" "tstop" } {
> +    foreach detach_method {"detach" "exit"} {
> +	foreach tstop {0 1} {
> +	    #Don't use tstop context if tstop is to be tested.
> +	    if {$command == "tstop" && $tstop} { } else {
> +		with_test_prefix "$command after $detach_method , tracing stopped: $tstop" {
> +		    do_test $command $detach_method $tstop
> +		}
> +	    }
> +	}
> +    }
> +}
> diff --git a/gdb/testsuite/lib/gdbserver-support.exp b/gdb/testsuite/lib/gdbserver-support.exp
> index 951afe5..9f65f60 100644
> --- a/gdb/testsuite/lib/gdbserver-support.exp
> +++ b/gdb/testsuite/lib/gdbserver-support.exp
> @@ -90,6 +90,10 @@ proc gdb_target_cmd { targetname serialport } {
>  	    -re "Timeout reading from remote system.*$gdb_prompt $" {
>  		verbose "Got timeout error from gdb."
>  	    }
> +	    -re "Connection timed out.*$gdb_prompt $" {
> +		verbose "Got timeout error from gdb."
> +	    }
> +
>  	    -notransfer -re "Remote debugging using .*\r\n> $" {
>  		# We got an unexpected prompt while creating the target.
>  		# Leave it there for the test to diagnose.

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