[PATCH] GDB/libiberty: Mingw32 remote debug hang on close
Maciej W. Rozycki
macro@codesourcery.com
Wed Dec 23 19:25:00 GMT 2009
Hello,
Noticed while debugging a remote target using pipes to communicate with a
debug stub both running on a Mingw32 host.
When a debug session is terminated from the GDB side, like with:
(gdb) kill
and the stub outputs any data to its stderr file descriptor (such as
diagnostic information) afterwards before it terminates, then both
programs hang.
I have tracked down the cause to be the parent pipe descriptor
corresponding to child's stderr having been left open while a wait() call
is made in the parent to await child's termination. Meanwhile the child
would keep producing diagnostic output to its stderr up till the
exhaustion of the pipe system buffer at which point the child would hang
as the parent busy with the wait() would not pay attention to its
corresponding descriptor anymore.
Here's a change that works for me. It makes sure the parent pipe
descriptors corresponding to child's stderr and stdout are closed before
the call to wait() is made, making any writes to these pipes in the child
fail straight away.
2009-12-23 Maciej W. Rozycki <macro@codesourcery.com>
libiberty/
* pex-common.c (pex_read_err): Set stderr_pipe to -1 if a
corresponding stream has been opened.
(pex_free): Close pipe file descriptors corresponding to child's
stdout and stderr before waiting.
Regression tested successfully with GDB testsuite the i386-mingw32 host
and the mips-sde-elf target, using QEMU as the remote system. OK to
apply?
Maciej
gdb-6.8.50-20091205-pex-free-0.patch
Index: libiberty/pex-common.c
===================================================================
--- libiberty/pex-common.c (revision 268718)
+++ libiberty/pex-common.c (working copy)
@@ -505,6 +505,7 @@ pex_read_err (struct pex_obj *obj, int b
if (o < 0 || o == STDIN_FILE_NO)
return NULL;
obj->read_err = obj->funcs->fdopenr (obj, o, binary);
+ obj->stderr_pipe = -1;
return obj->read_err;
}
@@ -597,8 +598,17 @@ pex_get_times (struct pex_obj *obj, int
void
pex_free (struct pex_obj *obj)
{
+ /* Close pipe file descriptors corresponding to child's stdout and
+ stderr so that the child does not hang trying to output anything
+ while we're waiting for it. */
if (obj->next_input >= 0 && obj->next_input != STDIN_FILE_NO)
obj->funcs->close (obj, obj->next_input);
+ if (obj->stderr_pipe >= 0 && obj->stderr_pipe != STDIN_FILE_NO)
+ obj->funcs->close (obj, obj->stderr_pipe);
+ if (obj->read_output != NULL)
+ fclose (obj->read_output);
+ if (obj->read_err != NULL)
+ fclose (obj->read_err);
/* If the caller forgot to wait for the children, we do it here, to
avoid zombies. */
@@ -619,10 +629,6 @@ pex_free (struct pex_obj *obj)
free (obj->status);
if (obj->time != NULL)
free (obj->time);
- if (obj->read_output != NULL)
- fclose (obj->read_output);
- if (obj->read_err != NULL)
- fclose (obj->read_err);
if (obj->remove_count > 0)
{
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