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Re: [PATCH] Handle vfork in thread with follow-fork-mode child
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?
>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}
+}
--
2.14.5