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Re: [PATCH] Handle vfork in thread with follow-fork-mode child
On 18-04-19 11:12, Pedro Alves wrote:
> On 4/18/19 9:02 AM, Tom de Vries wrote:
>> On 17-04-19 19:45, Pedro Alves wrote:
>>
>>> + inf->vfork_parent = NULL;
>>
>> I was checking this and found dereferences of inf->vfork_parent after it
>> was set to NULL here:
>> ...
>> else if (exec)
>> {
>> ...
>> resume_parent = inf->vfork_parent->pid;
>> ...
>> and here:
>> ...
>> else
>> {
>> ...
>> clone_program_space (pspace, inf->vfork_parent->pspace);
>> ...
>>
>> To confirm, I did another testrun with aborts at the start of the
>> blocks, and I found no regressions. So, either this is dead code, or we
>> need test-cases that trigger these paths.
>
> Indeed, I noticed this yesterday, fixed it & wrote the extra testing, but
> then had to leave for the day. Here is the updated patch with extra
> testing, which involved moving the body of the testcases to a procedure,
> and then testing with both "set detach-on-fork" "on" and "off".
>
> WDYT?
>
I've tested this both with native and native-gdbserver and found no
regressions.
I've also verified that both blocks mentioned above are triggered by the
new test-cases.
LGTM.
Thanks,
- Tom
> From 575fecd185d07cd0d2f9d9aed5325e7b09b675e0 Mon Sep 17 00:00:00 2001
> From: Pedro Alves <palves@redhat.com>
> Date: Thu, 18 Apr 2019 09:57:45 +0100
> Subject: [PATCH] [gdb] Handle vfork in thread with follow-fork-mode child
>
> When debugging any of the testcases added by this commit, which do a
> vfork in a thread with "set follow-fork-mode child" + "set
> detach-on-fork on", we run into this assertion:
>
> ...
> src/gdb/nat/x86-linux-dregs.c:146: internal-error: \
> void x86_linux_update_debug_registers(lwp_info*): \
> Assertion `lwp_is_stopped (lwp)' failed.
> ...
>
> The assert is caused by the following: the vfork-child exit or exec
> event is handled by handle_vfork_child_exec_or_exit, which calls
> target_detach to detach from the vfork parent. During target_detach
> we call linux_nat_target::detach, which:
>
> #1 - stops all the threads
> #2 - waits for all the threads to be stopped
> #3 - detaches all the threads
>
> However, during the second step we run into this code in
> stop_wait_callback:
>
> ...
> /* If this is a vfork parent, bail out, it is not going to report
> any SIGSTOP until the vfork is done with. */
> if (inf->vfork_child != NULL)
> return 0;
> ...
>
> and we don't wait for the threads to be stopped, which results in this
> assert in x86_linux_update_debug_registers triggering during the third
> step:
>
> ...
> gdb_assert (lwp_is_stopped (lwp));
> ...
>
> The fix is to reset the vfork parent's vfork_child field before
> calling target_detach in handle_vfork_child_exec_or_exit. There's
> already similar code for the other paths handled by
> handle_vfork_child_exec_or_exit, so this commit refactors the code a
> bit so that all paths share the same code.
>
> The new tests cover both a vfork child exiting, and a vfork child
> execing, since both cases would trigger the assertion.
>
> The new testcases also exercise following the vfork children with "set
> detach-on-fork off", since it doesn't seem to be tested anywhere.
>
> Tested on x86_64-linux, using native and native-gdbserver.
>
> gdb/ChangeLog:
> yyyy-mm-dd Tom de Vries <tdevries@suse.de>
> Pedro Alves <palves@redhat.com>
>
> PR gdb/24454
> * infrun.c (handle_vfork_child_exec_or_exit): Reset vfork parent's
> vfork_child field before calling target_detach.
>
> gdb/testsuite/ChangeLog:
> yyyy-mm-dd Tom de Vries <tdevries@suse.de>
> Pedro Alves <palves@redhat.com>
>
> PR gdb/24454
> * gdb.threads/vfork-follow-child-exec.c: New file.
> * gdb.threads/vfork-follow-child-exec.exp: New file.
> * gdb.threads/vfork-follow-child-exit.c: New file.
> * gdb.threads/vfork-follow-child-exit.exp: New file.
> ---
> gdb/infrun.c | 31 +++++-----
> .../gdb.threads/vfork-follow-child-exec.c | 66 ++++++++++++++++++++++
> .../gdb.threads/vfork-follow-child-exec.exp | 64 +++++++++++++++++++++
> .../gdb.threads/vfork-follow-child-exit.c | 52 +++++++++++++++++
> .../gdb.threads/vfork-follow-child-exit.exp | 60 ++++++++++++++++++++
> 5 files changed, 256 insertions(+), 17 deletions(-)
> create mode 100644 gdb/testsuite/gdb.threads/vfork-follow-child-exec.c
> create mode 100644 gdb/testsuite/gdb.threads/vfork-follow-child-exec.exp
> create mode 100644 gdb/testsuite/gdb.threads/vfork-follow-child-exit.c
> create mode 100644 gdb/testsuite/gdb.threads/vfork-follow-child-exit.exp
>
> diff --git a/gdb/infrun.c b/gdb/infrun.c
> index 37713b24fee..37df561de0b 100644
> --- a/gdb/infrun.c
> +++ b/gdb/infrun.c
> @@ -915,10 +915,14 @@ handle_vfork_child_exec_or_exit (int exec)
> int resume_parent = -1;
>
> /* This exec or exit marks the end of the shared memory region
> - between the parent and the child. If the user wanted to
> - detach from the parent, now is the time. */
> + between the parent and the child. Break the bonds. */
> + inferior *vfork_parent = inf->vfork_parent;
> + inf->vfork_parent->vfork_child = NULL;
> + inf->vfork_parent = NULL;
>
> - if (inf->vfork_parent->pending_detach)
> + /* If the user wanted to detach from the parent, now is the
> + time. */
> + if (vfork_parent->pending_detach)
> {
> struct thread_info *tp;
> struct program_space *pspace;
> @@ -926,7 +930,7 @@ handle_vfork_child_exec_or_exit (int exec)
>
> /* follow-fork child, detach-on-fork on. */
>
> - inf->vfork_parent->pending_detach = 0;
> + vfork_parent->pending_detach = 0;
>
> gdb::optional<scoped_restore_exited_inferior>
> maybe_restore_inferior;
> @@ -941,7 +945,7 @@ handle_vfork_child_exec_or_exit (int exec)
> maybe_restore_thread.emplace ();
>
> /* We're letting loose of the parent. */
> - tp = any_live_thread_of_inferior (inf->vfork_parent);
> + tp = any_live_thread_of_inferior (vfork_parent);
> switch_to_thread (tp);
>
> /* We're about to detach from the parent, which implicitly
> @@ -964,7 +968,7 @@ handle_vfork_child_exec_or_exit (int exec)
> if (print_inferior_events)
> {
> std::string pidstr
> - = target_pid_to_str (ptid_t (inf->vfork_parent->pid));
> + = target_pid_to_str (ptid_t (vfork_parent->pid));
>
> target_terminal::ours_for_output ();
>
> @@ -982,7 +986,7 @@ handle_vfork_child_exec_or_exit (int exec)
> }
> }
>
> - target_detach (inf->vfork_parent, 0);
> + target_detach (vfork_parent, 0);
>
> /* Put it back. */
> inf->pspace = pspace;
> @@ -997,10 +1001,7 @@ handle_vfork_child_exec_or_exit (int exec)
> inf->removable = 1;
> set_current_program_space (inf->pspace);
>
> - resume_parent = inf->vfork_parent->pid;
> -
> - /* Break the bonds. */
> - inf->vfork_parent->vfork_child = NULL;
> + resume_parent = vfork_parent->pid;
> }
> else
> {
> @@ -1030,17 +1031,13 @@ handle_vfork_child_exec_or_exit (int exec)
> set_current_program_space (pspace);
> inf->removable = 1;
> inf->symfile_flags = SYMFILE_NO_READ;
> - clone_program_space (pspace, inf->vfork_parent->pspace);
> + clone_program_space (pspace, vfork_parent->pspace);
> inf->pspace = pspace;
> inf->aspace = pspace->aspace;
>
> - resume_parent = inf->vfork_parent->pid;
> - /* Break the bonds. */
> - inf->vfork_parent->vfork_child = NULL;
> + resume_parent = vfork_parent->pid;
> }
>
> - inf->vfork_parent = NULL;
> -
> gdb_assert (current_program_space == inf->pspace);
>
> if (non_stop && resume_parent != -1)
> diff --git a/gdb/testsuite/gdb.threads/vfork-follow-child-exec.c b/gdb/testsuite/gdb.threads/vfork-follow-child-exec.c
> new file mode 100644
> index 00000000000..80632d1772f
> --- /dev/null
> +++ b/gdb/testsuite/gdb.threads/vfork-follow-child-exec.c
> @@ -0,0 +1,66 @@
> +/* This testcase is part of GDB, the GNU debugger.
> +
> + Copyright 2019 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 <stdio.h>
> +#include <unistd.h>
> +#include <pthread.h>
> +#include <string.h>
> +#include <stdlib.h>
> +
> +static char *program_name;
> +
> +static void *
> +f (void *arg)
> +{
> + int res = vfork ();
> +
> + if (res == -1)
> + {
> + perror ("vfork");
> + return NULL;
> + }
> + else if (res == 0)
> + {
> + /* Child. */
> + execl (program_name, program_name, "1", NULL);
> + perror ("exec");
> + abort ();
> + }
> + else
> + {
> + /* Parent. */
> + return NULL;
> + }
> +}
> +
> +int
> +main (int argc, char **argv)
> +{
> + pthread_t tid;
> +
> + if (argc > 1)
> + {
> + /* Getting here via execl. */
> + return 0;
> + }
> +
> + program_name = argv[0];
> +
> + pthread_create (&tid, NULL, f, NULL);
> + pthread_join (tid, NULL);
> + return 0;
> +}
> diff --git a/gdb/testsuite/gdb.threads/vfork-follow-child-exec.exp b/gdb/testsuite/gdb.threads/vfork-follow-child-exec.exp
> new file mode 100644
> index 00000000000..5a28715fa0d
> --- /dev/null
> +++ b/gdb/testsuite/gdb.threads/vfork-follow-child-exec.exp
> @@ -0,0 +1,64 @@
> +# Copyright (C) 2019 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/>. */
> +
> +# Test following a vfork child that execs, when the vfork parent is a
> +# threaded program, and it's a non-main thread that vforks.
> +
> +standard_testfile
> +
> +if {[build_executable "failed to prepare" $testfile $srcfile {debug pthreads}]} {
> + return -1
> +}
> +
> +# DETACH indicates whether "set detach-on-fork" is enabled. It is
> +# either "on" or "off".
> +
> +proc test_vfork {detach} {
> + global binfile
> +
> + clean_restart $binfile
> +
> + if ![runto_main] then {
> + fail "can't run to main"
> + return 0
> + }
> +
> + delete_breakpoints
> +
> + gdb_test_no_output "set follow-fork-mode child"
> + gdb_test_no_output "set detach-on-fork $detach"
> +
> + if {$detach == "off"} {
> + gdb_test "continue" \
> + [multi_line \
> + "Attaching after .* vfork to child .*" \
> + ".*New inferior 2 .*" \
> + ".* is executing new program: .*" \
> + ".*Inferior 2 .* exited normally.*"]
> + } else {
> + gdb_test "continue" \
> + [multi_line \
> + "Attaching after .* vfork to child .*" \
> + ".*New inferior 2 .*" \
> + ".*Detaching vfork parent process .* after child exec.*" \
> + ".*Inferior 1 .* detached.*" \
> + ".*is executing new program: .*" \
> + ".*Inferior 2 .*exited normally.*"]
> + }
> +}
> +
> +foreach_with_prefix detach-on-fork {"off" "on"} {
> + test_vfork ${detach-on-fork}
> +}
> diff --git a/gdb/testsuite/gdb.threads/vfork-follow-child-exit.c b/gdb/testsuite/gdb.threads/vfork-follow-child-exit.c
> new file mode 100644
> index 00000000000..6ae254cce96
> --- /dev/null
> +++ b/gdb/testsuite/gdb.threads/vfork-follow-child-exit.c
> @@ -0,0 +1,52 @@
> +/* This testcase is part of GDB, the GNU debugger.
> +
> + Copyright 2019 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 <stdio.h>
> +#include <unistd.h>
> +#include <pthread.h>
> +
> +static void *
> +f (void *arg)
> +{
> + int res = vfork ();
> +
> + if (res == -1)
> + {
> + perror ("vfork");
> + return NULL;
> + }
> + else if (res == 0)
> + {
> + /* Child. */
> + _exit (0);
> + }
> + else
> + {
> + /* Parent. */
> + return NULL;
> + }
> +}
> +
> +int
> +main (void)
> +{
> + pthread_t tid;
> +
> + pthread_create (&tid, NULL, f, NULL);
> + pthread_join (tid, NULL);
> + return 0;
> +}
> diff --git a/gdb/testsuite/gdb.threads/vfork-follow-child-exit.exp b/gdb/testsuite/gdb.threads/vfork-follow-child-exit.exp
> new file mode 100644
> index 00000000000..f07215d41c6
> --- /dev/null
> +++ b/gdb/testsuite/gdb.threads/vfork-follow-child-exit.exp
> @@ -0,0 +1,60 @@
> +# Copyright (C) 2019 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/>. */
> +
> +# Test following a vfork child that exits, when the vfork parent is a
> +# threaded program, and it's a non-main thread that vforks.
> +
> +standard_testfile
> +
> +if {[build_executable "failed to prepare" $testfile $srcfile {debug pthreads}]} {
> + return -1
> +}
> +
> +# DETACH indicates whether "set detach-on-fork" is enabled. It is
> +# either "on" or "off".
> +
> +proc test_vfork {detach} {
> + global binfile
> +
> + clean_restart $binfile
> +
> + if ![runto_main] then {
> + fail "can't run to main"
> + return 0
> + }
> +
> + gdb_test_no_output "set follow-fork-mode child"
> + gdb_test_no_output "set detach-on-fork $detach"
> +
> + if {$detach == "off"} {
> + gdb_test "continue" \
> + [multi_line \
> + "Attaching after .* vfork to child .*" \
> + ".*New inferior 2 .*" \
> + ".*Inferior 2 .*exited normally.*"]
> + } else {
> + gdb_test "continue" \
> + [multi_line \
> + "Attaching after .* vfork to child .*" \
> + ".*New inferior 2 .*" \
> + ".*Detaching vfork parent process .* after child exit.*" \
> + ".*Inferior 1 .* detached.*" \
> + ".*Inferior 2 .*exited normally.*"]
> + }
> +}
> +
> +foreach_with_prefix detach-on-fork {"off" "on"} {
> + test_vfork ${detach-on-fork}
> +}
>