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Always switch fork child to the main UI

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The following scenario:

 - gdb started in normal CLI mode.

 - separate MI channel created with new-ui

 - inferior output redirected with the "set inferior-tty" command.

 - use -exec-run in the MI channel to run the inferior

is presently mishandled.

When we create the inferior, in fork-child.c, right after vfork, we'll
close all the file descriptors in the vfork child, and then dup the
tty to file descriptors 0/1/2, create a session, etc.  Note that when
we close all descriptors, we close the file descriptors behind
gdb_stdin/gdb_stdout/gdb_stderr of all secondary UIs...  So if
anything goes wrong in the child and it calls warning/error, it'll end
up writting to the current UI's stdout/stderr streams, which are
backed by file descriptors that have since been closed.  Because this
happens in a vfork region, the corresponding stdin/stdout/stderr in
the parent/gdb end up corrupted.

The fix is to switch to the main UI right after the vfork, so that
gdb_stdin/gdb_stdout/gdb_stderr are correctly mapped to
stdin/stdout/stderr (and thus to file descriptors 0/1/2), so this code
works as it has always worked.

(Technically, we're doing a lot of stuff we shouldn't be doing after a
vfork, while we should only be calling async-signal-safe functions.)

gdb/ChangeLog:
2016-06-21  Pedro Alves  <palves@redhat.com>

	* fork-child.c (fork_inferior): Switch the child to the main UI
	right after vfork.  Save/restore the current UI in the parent.
	Flush outputs of the main UI instead of the current UI.

gdb/testsuite/ChangeLog:
2016-06-21  Pedro Alves  <palves@redhat.com>

	* gdb.mi/mi-exec-run.exp: New file.
This commit is contained in:
Pedro Alves 2016-06-21 01:11:57 +01:00
parent ef274d26b5
commit 49940788ab
4 changed files with 188 additions and 2 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

6
gdb/ChangeLog
View file

@ -1,3 +1,9 @@
2016-06-21 Pedro Alves <palves@redhat.com>
* fork-child.c (fork_inferior): Switch the child to the main UI
right after vfork. Save/restore the current UI in the parent.
Flush outputs of the main UI instead of the current UI.
2016-06-21 Pedro Alves <palves@redhat.com>
* breakpoint.c (watchpoint_check): Send watchpoint-deleted output

22
gdb/fork-child.c
View file

@ -31,6 +31,7 @@
#include "gdbcmd.h"
#include "solib.h"
#include "filestuff.h"
#include "top.h"
#include <signal.h>
@ -141,6 +142,7 @@ fork_inferior (char *exec_file_arg, char *allargs, char **env,
struct inferior *inf;
int i;
int save_errno;
struct ui *save_ui;
/* If no exec file handed to us, get it from the exec-file command
-- with a good, common error message if none is specified. */
@ -275,6 +277,9 @@ fork_inferior (char *exec_file_arg, char *allargs, char **env,
restore it. */
save_our_env = environ;
/* Likewise the current UI. */
save_ui = current_ui;
/* Tell the terminal handling subsystem what tty we plan to run on;
it will just record the information for later. */
new_tty_prefork (inferior_io_terminal);
@ -282,8 +287,8 @@ fork_inferior (char *exec_file_arg, char *allargs, char **env,
/* It is generally good practice to flush any possible pending stdio
output prior to doing a fork, to avoid the possibility of both
the parent and child flushing the same data after the fork. */
gdb_flush (gdb_stdout);
gdb_flush (gdb_stderr);
gdb_flush (main_ui->m_gdb_stdout);
gdb_flush (main_ui->m_gdb_stderr);
/* If there's any initialization of the target layers that must
happen to prepare to handle the child we're about fork, do it
@ -312,6 +317,16 @@ fork_inferior (char *exec_file_arg, char *allargs, char **env,
if (pid == 0)
{
/* Switch to the main UI, so that gdb_std{in/out/err} in the
child are mapped to std{in/out/err}. This makes it possible
to use fprintf_unfiltered/warning/error/etc. in the child
from here on. */
current_ui = main_ui;
/* Close all file descriptors except those that gdb inherited
(usually 0/1/2), so they don't leak to the inferior. Note
that this closes the file descriptors of all secondary
UIs. */
close_most_fds ();
if (debug_fork)
@ -378,6 +393,9 @@ fork_inferior (char *exec_file_arg, char *allargs, char **env,
/* Restore our environment in case a vforked child clob'd it. */
environ = save_our_env;
/* Likewise the current UI. */
current_ui = save_ui;
if (!have_inferiors ())
init_thread_list ();

4
gdb/testsuite/ChangeLog
View file

@ -1,3 +1,7 @@
2016-06-21 Pedro Alves <palves@redhat.com>
* gdb.mi/mi-exec-run.exp: New file.
2016-06-21 Pedro Alves <palves@redhat.com>
* gdb.mi/mi-break.exp (test_breakpoint_commands): Always expect

158
gdb/testsuite/gdb.mi/mi-exec-run.exp Normal file
View file

@ -0,0 +1,158 @@
# 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/>.
# Test that -exec-run works as expected. Exercises various testing
# axes:
#
# - MI running on main UI vs separate UI.
#
# - inferior tty set to main tty vs separate tty.
#
# - forking the child failing and sending output to the right inferior
# terminal, vs the child not failing to start.
load_lib mi-support.exp
set MIFLAGS "-i=mi"
# The purpose of this testcase is to test the -exec-run command. If we
# cannot use it, then there is no point in running this testcase.
if [target_info exists use_gdb_stub] {
untested "cannot use -exec-run command"
return -1
}
standard_testfile mi-start.c
if { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug}] != "" } {
untested "could not build mi-exec-run"
return -1
}
# The test proper. INFTTY_MODE determines whether "set inferior-tty"
# is in effect. MI_MODE determines whether MI is run on the main UI,
# or as a separate UI. FORCE_FAIL is true when we want -exec-run to
# fail and cause inferior output be sent to the inferior tty.
proc test {inftty_mode mi_mode force_fail} {
global srcdir subdir binfile srcfile
global gdb_spawn_id gdb_main_spawn_id mi_spawn_id inferior_spawn_id
global decimal
mi_gdb_exit
set start_ops {}
if {$inftty_mode == "separate"} {
lappend start_ops "separate-inferior-tty"
}
if {$mi_mode == "separate"} {
lappend start_ops "separate-mi-tty"
}
if [eval mi_gdb_start $start_ops] {
return
}
if {$force_fail} {
# Disable the shell so that its the first exec that fails,
# instead of the shell starting and then failing with some
# unspecified output.
mi_gdb_test "-gdb-set startup-with-shell off" ".*"
set bin $binfile.nox
} else {
set bin $binfile
}
mi_delete_breakpoints
mi_gdb_reinitialize_dir $srcdir/$subdir
mi_gdb_reinitialize_dir $srcdir/$subdir
mi_gdb_load ${bin}
# Useful for debugging:
verbose -log "Channels:"
verbose -log " inferior_spawn_id=$inferior_spawn_id"
verbose -log " gdb_spawn_id=$gdb_spawn_id"
verbose -log " gdb_main_spawn_id=$gdb_main_spawn_id"
verbose -log " mi_spawn_id=$mi_spawn_id"
if {$force_fail} {
set saw_perm_error 0
set saw_mi_error 0
set test "run failure detected"
send_gdb "-exec-run --start\n"
while {1} {
gdb_expect {
-i "$inferior_spawn_id"
-re ".*Cannot exec.*Permission denied" {
set saw_perm_error 1
verbose -log "saw mi error"
}
-i "$gdb_spawn_id"
-re "\\^error,msg=\"During startup program exited with code 127" {
set saw_mi_error 1
verbose -log "saw mi error"
}
timeout {
fail "$test (timeout)"
break
}
-i "$gdb_main_spawn_id"
eof {
fail "$test (eof)"
break
}
}
if {$saw_perm_error && $saw_mi_error} {
pass $test
break
}
}
} else {
mi_run_cmd "--start"
mi_expect_stop "breakpoint-hit" "main" "" ".*$srcfile" "$decimal" \
{ "" "disp=\"del\"" } "breakpoint hit reported on mi"
if {$mi_mode == "separate"} {
# Check that the breakpoint hit is reported on the main
# UI/CLI. Note no prompt is expected.
switch_gdb_spawn_id $gdb_main_spawn_id
set test "breakpoint hit reported on console"
gdb_test_multiple "" $test {
-re "Temporary breakpoint .*, main \\(\\) at .*$srcfile:$decimal.*return 0;" {
pass $test
}
}
# Switch back to the MI UI.
global mi_spawn_id
switch_gdb_spawn_id $mi_spawn_id
}
}
}
# Create a not-executable copy of the program, in order to exercise
# vfork->exec failing.
gdb_remote_download host $binfile $binfile.nox
remote_spawn target "chmod \"a-x\" $binfile.nox"
foreach_with_prefix inferior-tty {"main" "separate"} {
foreach_with_prefix mi {"main" "separate"} {
foreach_with_prefix force-fail {0 1} {
test ${inferior-tty} ${mi} ${force-fail}
}
}
}