gdb pty problem [Was: emacs gud-interface is not updated after gdb command execution (maybe because of incomplete output from gdb)]

Wed Jun 1 12:51:00 GMT 2016

On 5/31/2016 5:41 AM, Corinna Vinschen wrote:
> Any chance you could bisect Cygwin to help finding the culprit?

The culprit is
commit 252a07b0ad3353abcd0fcd9b1b65ff977acd679e
Author: Takashi Yano <takashi.yano@nifty.ne.jp>
Date: Fri Apr 3 13:07:35 2015 +0900
 Cygwin hangs up if several keys are typed during outputting a lot of texts.
 * fhandler_tty.cc (fhandler_pty_slave::read): Change calculation of
 "readlen" not to use "bytes_in_pipe" value directly.
Reverting that commit fixes the problem. To test, compile and run the attached file.
$ gcc gdbstc.cc
$ ./a
1-inferior-tty-set /dev/pty3
2-gdb-set height 0
3-gdb-set non-stop 1
4-file-list-exec-source-files
5-file-list-exec-source-file
6-gdb-show prompt
7-stack-info-frame
8-thread-info
9-break-list
q
*** using gdb
=thread-group-added,id="i1"
~"GNU gdb (GDB) (Cygwin 7.10.1-1) 7.10.1\n"
~"Copyright (C) 2015 Free Software Foundation, Inc.\n"
~"License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>\nThis is free software: you are free to change and redistribute it.\nThere is NO WARRANTY, to the extent permitted by law. Type \"show copying\"\nand \"show warranty\" for details.\n"
~"This GDB was configured as \"i686-pc-cygwin\".\nType \"show configuration\" for configuration details."
~"\nFor bug reporting instructions, please see:\n"
~"<http://www.gnu.org/software/gdb/bugs/>.\n"
~"Find the GDB manual and other documentation resources online at:\n<http://www.gnu.org/software/gdb/documentation/>.\n"
~"For help, type \"help\".\n"
~"Type \"apropos word\" to search for commands related to \"word\".\n"
=cmd-param-changed,param="auto-load safe-path",value="/"
(gdb)
...
In bad cases (bug present), the program hangs and doesn't complete until the gdb process is killed from a different terminal. In good cases it runs to completion.
Ken
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#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pty.h>
#include <string.h>
#include <sys/wait.h>
void get_output (int fd);
int
main (int argc, const char **argv) 
{
 int master;
 pid_t pid;
 if ((pid = forkpty (&master, NULL, NULL, NULL)) < 0)
 {
 perror ("forkpty");
 exit (1);
 }
 /* child */
 if (pid == 0) 
 {
 const char *av[100];
 // putenv ("HOME=/tmp");
 int i = 0;
#ifdef STRACE_GDB
 av[i++] = "strace";
 av[i++] = "-o";
 av[i++] = "/tmp/strace.out";
#ifdef __CYGWIN__
 av[i++] = "--mask=all+paranoid";
#endif
#endif
 av[i++] = argv[1] ?: "gdb";
 fprintf (stderr, "*** using %s\n", av[0]);
 av[i++] = "-i=mi";
 av[i] = NULL;
 execvp (av[0], (char * const *) av);
 /* shouldn't get here */
 exit (1);
 }
 /* parent */
 const char *input[20];
 int i = 0;
 input[i++] = "1-inferior-tty-set /dev/pty3\n";
 input[i++] = "2-gdb-set height 0\n";
 input[i++] = "3-gdb-set non-stop 1\n";
 input[i++] = "4-file-list-exec-source-files\n";
 input[i++] = "5-file-list-exec-source-file\n";
 input[i++] = "6-gdb-show prompt\n";
 input[i++] = "7-stack-info-frame\n";
 input[i++] = "8-thread-info\n";
 input[i++] = "9-break-list\n";
 input[i++] = "q\n";
 input[i] = NULL;
 for (int i = 0; input[i]; ++i)
 {
 write (master, input[i], strlen (input[i]));
 // sleep (1);
 }
 get_output (master);
 wait (NULL);
}
void
get_output (int fd)
{
 char buf[4096];
 while (1)
 {
 int nread = read (fd, buf, sizeof (buf));
 if (nread > 0)
	write (STDOUT_FILENO, buf, nread);
 else
	{
	 printf ("No more output. nread %d\n", nread);
	 break;
	}
 }
}
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