[PATCH]Fix that GDB will get hang on Windows when using pipe to get stdout and stderr from stub
Terry Guo
terry.guo@arm.com
Wed Jul 4 08:19:00 GMT 2012
Hi Eli,
> -----Original Message-----
> From: Eli Zaretskii [mailto:eliz@gnu.org]
> Sent: Thursday, June 28, 2012 12:54 AM
> To: Terry Guo
> Cc: gdb-patches@sourceware.org; Joey Ye; Matthew Gretton-Dann;
> palves@redhat.com; daniel.jacobowitz@gmail.com
> Subject: Re: [PATCH]Fix that GDB will get hang on Windows when using
> pipe to get stdout and stderr from stub
>
> > From: "Terry Guo" <terry.guo@arm.com>
> > Cc: <eliz@gnu.org>,
> > "Joey Ye" <Joey.Ye@arm.com>,
> > "Matthew Gretton-Dann" <Matthew.Gretton-Dann@arm.com>,
> > "'Pedro Alves'" <palves@redhat.com>,
> > <daniel.jacobowitz@gmail.com>
> > Date: Tue, 26 Jun 2012 09:13:14 +0800
> >
> > I noticed a cross-built MINGW arm-none-eabi GDB will get hang on
> Windows
> > when use pipe to get stderr and stdout from stub. The command used to
> start
> > stub in GDB is "target extended-remote |
> > stub-that-write-stderr-before-stdout". For my case, after send
> > "$vFlashDone#ea" to stub, GDB get hang. The GDB source show that GDB
> will
> > keep waiting for ACK message from stdout of stub, after send the
> packet.
> > Unfortunately my stub will write some kind of log information into
> stderr
> > and this action takes place before stub write ACK message to its
> stdout. So
> > the only pipe is occupied by stderr which is waiting for GDB to
> consume,
> > while GDB keep waiting for message from the stdout which hasn't pipe
> to use.
> > We finally end up with a deadlock on pipe between GDB/stderr/stdout.
> >
> > The following patch can avoid such deadlock by letting GDB also probe
> and
> > consume stderr when waiting for stdout. Please review and comment.
>
> I only read it superficially, but it looked fine to me.
>
> Thanks.
Thanks for your review. Here I updated my patch to make it more robust. No
changes on its functions. Please help to review again. Thanks.
The original patch is at:
http://sourceware.org/ml/gdb-patches/2012-06/msg00790.html
BR,
Terry
2012-07-04 Terry Guo <terry.guo@arm.com>
* defs.h (GDB_MI_MSG_WIDTH): New.
* ser_base (ser_base_read_error_fd): New function.
(do_ser_base_readchar): Poll error file descriptor as well as
standard output.
(generic_readchar): Refactor error handling.
diff --git a/gdb/defs.h b/gdb/defs.h
index 9531c5a..303721b 100644
--- a/gdb/defs.h
+++ b/gdb/defs.h
@@ -1214,6 +1214,9 @@ extern int use_windows;
#define ISATTY(FP) (isatty (fileno (FP)))
#endif
+/* A width that can achieve a better legibility for GDB MI mode. */
+#define GDB_MI_MSG_WIDTH 80
+
/* Ensure that V is aligned to an N byte boundary (B's assumed to be a
power of 2). Round up/down when necessary. Examples of correct
use include:
diff --git a/gdb/ser-base.c b/gdb/ser-base.c
index 368afa6..661c5a9 100644
--- a/gdb/ser-base.c
+++ b/gdb/ser-base.c
@@ -26,6 +26,7 @@
#include "gdb_select.h"
#include "gdb_string.h"
+#include "gdb_assert.h"
#include <sys/time.h>
#ifdef USE_WIN32API
#include <winsock2.h>
@@ -223,6 +224,64 @@ ser_base_wait_for (struct serial *scb, int timeout)
}
}
+/* Read any error output we might have. */
+
+void
+ser_base_read_error_fd (struct serial *scb, int close_fd)
+{
+ if (scb->error_fd != -1)
+ {
+ ssize_t s;
+ char buf[GDB_MI_MSG_WIDTH + 1];
+
+ for (;;)
+ {
+ char *current;
+ char *newline;
+ int to_read = GDB_MI_MSG_WIDTH;
+ int num_bytes = -1;
+
+ if (scb->ops->avail)
+ num_bytes = (scb->ops->avail)(scb, scb->error_fd);
+
+ if (num_bytes != -1)
+ to_read = (num_bytes < to_read) ? num_bytes : to_read;
+
+ if (to_read == 0)
+ break;
+
+ s = read (scb->error_fd, &buf, to_read);
+ if ((s == -1) || (s == 0 && !close_fd))
+ break;
+
+ if (s == 0 && close_fd)
+ {
+ /* End of file. */
+ close (scb->error_fd);
+ scb->error_fd = -1;
+ break;
+ }
+
+ /* In theory, embedded newlines are not a problem.
+ But for MI, we want each output line to have just
+ one newline for legibility. So output things
+ in newline chunks. */
+ gdb_assert (s > 0 && s <= GDB_MI_MSG_WIDTH);
+ buf[s] = '\0';
+ current = buf;
+ while ((newline = strstr (current, "\n")) != NULL)
+ {
+ *newline = '\0';
+ fputs_unfiltered (current, gdb_stderr);
+ fputs_unfiltered ("\n", gdb_stderr);
+ current = newline + 1;
+ }
+
+ fputs_unfiltered (current, gdb_stderr);
+ }
+ }
+}
+
/* Read a character with user-specified timeout. TIMEOUT is number of
seconds
to wait, or -1 to wait forever. Use timeout of 0 to effect a poll.
Returns
char if successful. Returns -2 if timeout expired, EOF if line dropped
@@ -273,6 +332,11 @@ do_ser_base_readchar (struct serial *scb, int timeout)
status = SERIAL_TIMEOUT;
break;
}
+
+ /* We also need to check and consume the stderr because it could
+ come before the stdout for some stubs. If we just sit and wait
+ for stdout, we would hit a deadlock for that case. */
+ ser_base_read_error_fd (scb, 0);
}
if (status < 0)
@@ -344,53 +408,7 @@ generic_readchar (struct serial *scb, int timeout,
}
}
/* Read any error output we might have. */
- if (scb->error_fd != -1)
- {
- ssize_t s;
- char buf[81];
-
- for (;;)
- {
- char *current;
- char *newline;
- int to_read = 80;
-
- int num_bytes = -1;
- if (scb->ops->avail)
- num_bytes = (scb->ops->avail)(scb, scb->error_fd);
- if (num_bytes != -1)
- to_read = (num_bytes < to_read) ? num_bytes : to_read;
-
- if (to_read == 0)
- break;
-
- s = read (scb->error_fd, &buf, to_read);
- if (s == -1)
- break;
- if (s == 0)
- {
- /* EOF */
- close (scb->error_fd);
- scb->error_fd = -1;
- break;
- }
-
- /* In theory, embedded newlines are not a problem.
- But for MI, we want each output line to have just
- one newline for legibility. So output things
- in newline chunks. */
- buf[s] = '\0';
- current = buf;
- while ((newline = strstr (current, "\n")) != NULL)
- {
- *newline = '\0';
- fputs_unfiltered (current, gdb_stderr);
- fputs_unfiltered ("\n", gdb_stderr);
- current = newline + 1;
- }
- fputs_unfiltered (current, gdb_stderr);
- }
- }
+ ser_base_read_error_fd (scb, 1);
reschedule (scb);
return ch;
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