binutils-gdb/gdb/testsuite/gdb.threads/vfork-follow-child-exit.exp
Tom de Vries b73715df01 [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:
2019-04-18  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:
2019-04-18  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.
2019-04-18 17:05:43 +01:00

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# 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}
}