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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
Download Patch File Download Diff File Expand all files Collapse all files

22
gdb/fork-child.c
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@@ -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 ();