+2010-02-22 Joel E. Denny <jdenny@ces.clemson.edu>
+
+ portability: fix several issues with M4 subprocess.
+
+ M4's output pipe was not being drained upon fatal errors during
+ scan_skel. As a result, broken-pipe messages from M4 were seen
+ on at least AIX, HP-UX, Solaris, and RHEL4, and this caused a
+ failure in the test suite. The problem was that, on platforms
+ where the default disposition for SIGPIPE is ignore instead of
+ terminate, M4 sometimes saw fwrite fail with errno=EPIPE and
+ then reported it. However, there's some sort of race condition,
+ because the new test group occasionally succeeded.
+ Reported by Albert Chin at
+ <http://lists.gnu.org/archive/html/bug-bison/2010-02/msg00004.html>.
+
+ There were also problems with the test suite livelocking on
+ Tru64 5.1b. Reported by Didier Godefroy at
+ <http://lists.gnu.org/archive/html/bug-bison/2009-05/msg00005.html>.
+ Switching to create_pipe_bidi suggested by Akim Demaille.
+
+ To attempt to solve both of these problems, switch to gnulib's
+ create_pipe_bidi and register M4 process as a slave. Along the
+ way, clean up file name conflict handling, which was affected by
+ the broken-pipe problem before the switch.
+ * NEWS (2.4.2): Document.
+ * THANKS (Didier Godefroy): Add.
+ * bootstrap.conf (gnulib_modules): Add pipe.
+ * gnulib: Update to latest to make sure we have all the latest
+ fixes.
+ * lib/Makefile.am (libbison_a_SOURCES): Remove subpipe.h and
+ subpipe.c.
+ * po/POTFILES.in (lib/subpipe.c): Remove.
+ * src/files.c (compute_output_file_names): Update invocations
+ of output_file_name_check.
+ (output_file_name_check): In the case that the grammar file
+ would be overwritten, use complain instead of fatal, but replace
+ the output file name with /dev/null. Use the /dev/null solution
+ for the case of two conflicting output files as well because it
+ seems safer in case Bison one day tries to open both files at
+ the same time.
+ * src/files.h (output_file_name_check): Update prototype.
+ * src/output.c (output_skeleton): Use create_pipe_bidi and
+ wait_subprocess. Assert that scan_skel completely drains the
+ pipe.
+ * src/scan-skel.l (at_directive_perform): Update
+ output_file_name_check invocation.
+ * tests/output.at (AT_CHECK_CONFLICTING_OUTPUT): Check that the
+ grammar file actually isn't overwritten.
+ (Conflicting output files: -o foo.y): Update expected output.
+ * tests/skeletons.at (Fatal errors but M4 continues producing
+ output): New test group.
+
2010-02-04 Joel E. Denny <jdenny@ces.clemson.edu>
Update POTFILES.
* Changes in version 2.4.2 (????-??-??):
-** Some portability problems in the testsuite that resulted in failures
- on at least Solaris 2.7 have been fixed.
+** Some portability problems that resulted in failures and livelocks
+ in the test suite on some versions of at least Solaris, AIX, HP-UX,
+ RHEL4, and Tru64 have been fixed. As part of those fixes, fatal
+ Bison errors no longer cause M4 to report a broken pipe on the
+ affected platforms.
** `%prec IDENTIFIER' requires IDENTIFIER to be defined separately.
Derek M. Jones derek@knosof.co.uk
Di-an Jan dianj@freeshell.org
Dick Streefland dick.streefland@altium.nl
+Didier Godefroy dg@ulysium.net
Enrico Scholz enrico.scholz@informatik.tu-chemnitz.de
Eric Blake ebb9@byu.net
Evgeny Stambulchik fnevgeny@plasma-gate.weizmann.ac.il
announce-gen argmatch assert config-h c-strcase configmake dirname
error extensions fopen-safer gendocs getopt-gnu gettext
git-version-gen hash inttypes javacomp-script javaexec-script
- maintainer-makefile malloc mbswidth obstack quote quotearg stdbool
- stpcpy strerror strtoul strverscmp unistd unistd-safer unlocked-io
- update-copyright unsetenv verify warnings xalloc xalloc-die xstrndup
+ maintainer-makefile malloc mbswidth obstack pipe quote quotearg
+ stdbool stpcpy strerror strtoul strverscmp unistd unistd-safer
+ unlocked-io update-copyright unsetenv verify warnings xalloc
+ xalloc-die xstrndup
'
# Additional xgettext options to use. Use "\\\newline" to break lines.
-Subproject commit 102c411be0dfd9ac6aa0bb6450415e87bf0842ca
+Subproject commit 9d0ad652de159d08e5f679842f8a2a5658196361
.deps
Makefile
Makefile.in
+alloca.h
+alloca.in.h
argmatch.c
argmatch.h
basename-lgpl.c
basename.c
+binary-io.h
bitrotate.h
c-ctype.c
c-ctype.h
c-strcasecmp.c
c-strncasecmp.c
charset.alias
+cloexec.c
+cloexec.h
config.charset
config.h
config.hin
dirname-lgpl.c
dirname.c
dirname.h
+dup-safer-flag.c
dup-safer.c
dup2.c
errno.h
error.h
exitfail.c
exitfail.h
+fatal-signal.c
+fatal-signal.h
fcntl.c
fcntl.h
fcntl.in.h
+fd-safer-flag.c
fd-safer.c
fopen-safer.c
fopen.c
+getdtablesize.c
getopt.c
getopt.h
getopt.in.h
memchr.valgrind
obstack.c
obstack.h
+open.c
pipe-safer.c
+pipe.c
+pipe.h
+pipe2-safer.c
+pipe2.c
quote.c
quote.h
quotearg.c
quotearg.h
+rawmemchr.c
+rawmemchr.valgrind
ref-add.sed
ref-add.sin
ref-del.sed
ref-del.sin
+sched.h
+sched.in.h
+sig-handler.h
+sigaction.c
+signal.h
+signal.in.h
+sigprocmask.c
+spawn.h
+spawn.in.h
+spawn_faction_addclose.c
+spawn_faction_adddup2.c
+spawn_faction_addopen.c
+spawn_faction_destroy.c
+spawn_faction_init.c
+spawn_int.h
+spawnattr_destroy.c
+spawnattr_init.c
+spawnattr_setflags.c
+spawnattr_setsigmask.c
+spawni.c
+spawnp.c
stamp-h1
+stat.c
stdbool.h
stdbool.in.h
stdbool_.h
stdlib.in.h
stdlib_.h
stpcpy.c
+strchrnul.c
+strchrnul.valgrind
streq.h
strerror.c
string.h
strtoul.c
strverscmp.c
strverscmp.h
+sys
+sys_stat.h
+sys_stat.in.h
+sys_wait.h
+sys_wait.in.h
+time.h
+time.in.h
unistd--.h
unistd-safer.h
unistd.h
unlocked-io.h
unsetenv.c
verify.h
+w32spawn.h
+wait-process.c
+wait-process.h
wchar.h
wchar.in.h
wchar_.h
/.deps
/Makefile
/Makefile.in
+/alloca.h
+/alloca.in.h
/argmatch.c
/argmatch.h
/basename-lgpl.c
/basename.c
+/binary-io.h
/bitrotate.h
/c-ctype.c
/c-ctype.h
/c-strcasecmp.c
/c-strncasecmp.c
/charset.alias
+/cloexec.c
+/cloexec.h
/config.charset
/config.h
/config.hin
/dirname-lgpl.c
/dirname.c
/dirname.h
+/dup-safer-flag.c
/dup-safer.c
/dup2.c
/errno.h
/error.h
/exitfail.c
/exitfail.h
+/fatal-signal.c
+/fatal-signal.h
/fcntl.c
/fcntl.h
/fcntl.in.h
+/fd-safer-flag.c
/fd-safer.c
/fopen-safer.c
/fopen.c
+/getdtablesize.c
/getopt.c
/getopt.h
/getopt.in.h
/memchr.valgrind
/obstack.c
/obstack.h
+/open.c
/pipe-safer.c
+/pipe.c
+/pipe.h
+/pipe2-safer.c
+/pipe2.c
/quote.c
/quote.h
/quotearg.c
/quotearg.h
+/rawmemchr.c
+/rawmemchr.valgrind
/ref-add.sed
/ref-add.sin
/ref-del.sed
/ref-del.sin
+/sched.h
+/sched.in.h
+/sig-handler.h
+/sigaction.c
+/signal.h
+/signal.in.h
+/sigprocmask.c
+/spawn.h
+/spawn.in.h
+/spawn_faction_addclose.c
+/spawn_faction_adddup2.c
+/spawn_faction_addopen.c
+/spawn_faction_destroy.c
+/spawn_faction_init.c
+/spawn_int.h
+/spawnattr_destroy.c
+/spawnattr_init.c
+/spawnattr_setflags.c
+/spawnattr_setsigmask.c
+/spawni.c
+/spawnp.c
/stamp-h1
+/stat.c
/stdbool.h
/stdbool.in.h
/stdbool_.h
/stdlib.in.h
/stdlib_.h
/stpcpy.c
+/strchrnul.c
+/strchrnul.valgrind
/streq.h
/strerror.c
/string.h
/strtoul.c
/strverscmp.c
/strverscmp.h
+/sys
+/sys_stat.h
+/sys_stat.in.h
+/sys_wait.h
+/sys_wait.in.h
+/time.h
+/time.in.h
/unistd--.h
/unistd-safer.h
/unistd.h
/unlocked-io.h
/unsetenv.c
/verify.h
+/w32spawn.h
+/wait-process.c
+/wait-process.h
/wchar.h
/wchar.in.h
/wchar_.h
# Non-gnulib sources in Bison's internal library.
libbison_a_SOURCES += \
get-errno.h get-errno.c \
- subpipe.h subpipe.c \
$(bitsets_sources) $(additional_bitsets_sources) $(timevars_sources)
# The Yacc compatibility library.
+++ /dev/null
-/* Subprocesses with pipes.
-
- Copyright (C) 2002, 2004-2006, 2009-2010 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/>. */
-
-/* Written by Paul Eggert <eggert@twinsun.com>
- and Florian Krohm <florian@edamail.fishkill.ibm.com>. */
-
-#include <config.h>
-
-#include "subpipe.h"
-
-#include <errno.h>
-
-#include <signal.h>
-#if ! defined SIGCHLD && defined SIGCLD
-# define SIGCHLD SIGCLD
-#endif
-
-#include <stdlib.h>
-
-#include <unistd.h>
-#ifndef STDIN_FILENO
-# define STDIN_FILENO 0
-#endif
-#ifndef STDOUT_FILENO
-# define STDOUT_FILENO 1
-#endif
-#if ! HAVE_DUP2 && ! defined dup2
-# include <fcntl.h>
-# define dup2(f, t) (close (t), fcntl (f, F_DUPFD, t))
-#endif
-
-#if HAVE_SYS_WAIT_H
-# include <sys/wait.h>
-#endif
-#ifndef WEXITSTATUS
-# define WEXITSTATUS(stat_val) ((unsigned int) (stat_val) >> 8)
-#endif
-#ifndef WIFEXITED
-# define WIFEXITED(stat_val) (((stat_val) & 255) == 0)
-#endif
-
-#if HAVE_VFORK_H
-# include <vfork.h>
-#endif
-#if ! HAVE_WORKING_VFORK
-# define vfork fork
-#endif
-
-#include "error.h"
-#include "unistd-safer.h"
-
-#include "gettext.h"
-#define _(Msgid) gettext (Msgid)
-
-#ifndef __attribute__
-/* This feature is available in gcc versions 2.5 and later. */
-# if ! defined __GNUC__ || __GNUC__ < 2 || \
-(__GNUC__ == 2 && __GNUC_MINOR__ < 5) || __STRICT_ANSI__
-# define __attribute__(Spec) /* empty */
-# endif
-#endif
-
-#ifndef ATTRIBUTE_UNUSED
-# define ATTRIBUTE_UNUSED __attribute__ ((__unused__))
-#endif
-
-
-/* Initialize this module. */
-
-void
-init_subpipe (void)
-{
-#ifdef SIGCHLD
- /* System V fork+wait does not work if SIGCHLD is ignored. */
- signal (SIGCHLD, SIG_DFL);
-#endif
-}
-
-
-/* Create a subprocess that is run as a filter. ARGV is the
- NULL-terminated argument vector for the subprocess. Store read and
- write file descriptors for communication with the subprocess into
- FD[0] and FD[1]: input meant for the process can be written into
- FD[0], and output from the process can be read from FD[1]. Return
- the subprocess id.
-
- To avoid deadlock, the invoker must not let incoming data pile up
- in FD[1] while writing data to FD[0]. */
-
-pid_t
-create_subpipe (char const * const *argv, int fd[2])
-{
- int pipe_fd[2];
- int child_fd[2];
- pid_t pid;
-
- if (pipe_safer (child_fd) != 0 || pipe_safer (pipe_fd) != 0)
- error (EXIT_FAILURE, errno, "pipe");
- fd[0] = child_fd[1];
- fd[1] = pipe_fd[0];
- child_fd[1] = pipe_fd[1];
-
- pid = vfork ();
- if (pid < 0)
- error (EXIT_FAILURE, errno, "fork");
-
- if (! pid)
- {
- /* Child. */
- close (fd[0]);
- close (fd[1]);
- dup2 (child_fd[0], STDIN_FILENO);
- close (child_fd[0]);
- dup2 (child_fd[1], STDOUT_FILENO);
- close (child_fd[1]);
-
- /* The cast to (char **) rather than (char * const *) is needed
- for portability to older hosts with a nonstandard prototype
- for execvp. */
- execvp (argv[0], (char **) argv);
-
- _exit (errno == ENOENT ? 127 : 126);
- }
-
- /* Parent. */
- close (child_fd[0]);
- close (child_fd[1]);
- return pid;
-}
-
-
-/* Wait for the subprocess to exit. */
-
-void
-reap_subpipe (pid_t pid, char const *program)
-{
-#if HAVE_WAITPID || defined waitpid
- int wstatus;
- if (waitpid (pid, &wstatus, 0) < 0)
- error (EXIT_FAILURE, errno, "waitpid");
- else
- {
- int status = WIFEXITED (wstatus) ? WEXITSTATUS (wstatus) : -1;
- if (status)
- error (EXIT_FAILURE, 0,
- _(status == 126
- ? "subsidiary program `%s' could not be invoked"
- : status == 127
- ? "subsidiary program `%s' not found"
- : status < 0
- ? "subsidiary program `%s' failed"
- : "subsidiary program `%s' failed (exit status %d)"),
- program, status);
- }
-#endif
-}
-
-void
-end_of_output_subpipe (pid_t pid ATTRIBUTE_UNUSED,
- int fd[2] ATTRIBUTE_UNUSED)
-{
-}
+++ /dev/null
-/* Subprocesses with pipes.
- Copyright (C) 2002, 2004-2005, 2009-2010 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/>. */
-
-/* Written by Paul Eggert <eggert@twinsun.com>
- and Florian Krohm <florian@edamail.fishkill.ibm.com>. */
-
-#if HAVE_SYS_TYPES_H
-# include <sys/types.h>
-#endif
-
-void init_subpipe (void);
-pid_t create_subpipe (char const * const *, int[2]);
-void end_of_output_subpipe (pid_t, int[2]);
-void reap_subpipe (pid_t, char const *);
00gnulib.m4
absolute-header.m4
+alloca.m4
argmatch.m4
assert.m4
+cloexec.m4
config-h.m4
dirname.m4
dos.m4
error.m4
exitfail.m4
extensions.m4
+fatal-signal.m4
fcntl-o.m4
fcntl.m4
fcntl_h.m4
fopen.m4
+getdtablesize.m4
getopt.m4
getpagesize.m4
gettext.m4
mbswidth.m4
memchr.m4
mmap-anon.m4
+mode_t.m4
multiarch.m4
nls.m4
+open.m4
+pipe.m4
+pipe2.m4
po.m4
+posix_spawn.m4
progtest.m4
quote.m4
quotearg.m4
+rawmemchr.m4
+sched_h.m4
setenv.m4
+sig_atomic_t.m4
+sigaction.m4
+signal_h.m4
+signalblocking.m4
+spawn_h.m4
+stat.m4
stdbool.m4
stddef_h.m4
stdint.m4
stdio_h.m4
stdlib_h.m4
stpcpy.m4
+strchrnul.m4
strerror.m4
string_h.m4
strndup.m4
strtol.m4
strtoul.m4
strverscmp.m4
+sys_stat_h.m4
+sys_wait_h.m4
threadlib.m4
+time_h.m4
unistd-safer.m4
unistd_h.m4
unlocked-io.m4
+wait-process.m4
warn-on-use.m4
warning.m4
warnings.m4
/00gnulib.m4
/absolute-header.m4
+/alloca.m4
/argmatch.m4
/assert.m4
+/cloexec.m4
/config-h.m4
/dirname.m4
/dos.m4
/error.m4
/exitfail.m4
/extensions.m4
+/fatal-signal.m4
/fcntl-o.m4
/fcntl.m4
/fcntl_h.m4
/fopen.m4
+/getdtablesize.m4
/getopt.m4
/getpagesize.m4
/gettext.m4
/mbswidth.m4
/memchr.m4
/mmap-anon.m4
+/mode_t.m4
/multiarch.m4
/nls.m4
+/open.m4
+/pipe.m4
+/pipe2.m4
/po.m4
+/posix_spawn.m4
/progtest.m4
/quote.m4
/quotearg.m4
+/rawmemchr.m4
+/sched_h.m4
/setenv.m4
+/sig_atomic_t.m4
+/sigaction.m4
+/signal_h.m4
+/signalblocking.m4
+/spawn_h.m4
+/stat.m4
/stdbool.m4
/stddef_h.m4
/stdint.m4
/stdio_h.m4
/stdlib_h.m4
/stpcpy.m4
+/strchrnul.m4
/strerror.m4
/string_h.m4
/strndup.m4
/strtol.m4
/strtoul.m4
/strverscmp.m4
+/sys_stat_h.m4
+/sys_wait_h.m4
/threadlib.m4
+/time_h.m4
/unistd-safer.m4
/unistd_h.m4
/unlocked-io.m4
+/wait-process.m4
/warn-on-use.m4
/warning.m4
/warnings.m4
lib/getopt.c
lib/obstack.c
lib/quotearg.c
-lib/subpipe.c
lib/timevar.c
lib/xalloc-die.c
{
if (! spec_graph_file)
spec_graph_file = concat2 (all_but_tab_ext, ".dot");
- output_file_name_check (spec_graph_file);
+ output_file_name_check (&spec_graph_file);
}
if (xml_flag)
{
if (! spec_xml_file)
spec_xml_file = concat2 (all_but_tab_ext, ".xml");
- output_file_name_check (spec_xml_file);
+ output_file_name_check (&spec_xml_file);
}
if (report_flag)
{
if (!spec_verbose_file)
spec_verbose_file = concat2 (all_but_tab_ext, OUTPUT_EXT);
- output_file_name_check (spec_verbose_file);
+ output_file_name_check (&spec_verbose_file);
}
free (all_but_tab_ext);
}
void
-output_file_name_check (char const *file_name)
+output_file_name_check (char **file_name)
{
- if (0 == strcmp (file_name, grammar_file))
- fatal (_("refusing to overwrite the input file %s"), quote (file_name));
- {
- int i;
- for (i = 0; i < file_names_count; i++)
- if (0 == strcmp (file_names[i], file_name))
- warn (_("conflicting outputs to file %s"), quote (file_name));
- }
- file_names = xnrealloc (file_names, ++file_names_count, sizeof *file_names);
- file_names[file_names_count-1] = xstrdup (file_name);
+ bool conflict = false;
+ if (0 == strcmp (*file_name, grammar_file))
+ {
+ complain (_("refusing to overwrite the input file %s"),
+ quote (*file_name));
+ conflict = true;
+ }
+ else
+ {
+ int i;
+ for (i = 0; i < file_names_count; i++)
+ if (0 == strcmp (file_names[i], *file_name))
+ {
+ warn (_("conflicting outputs to file %s"),
+ quote (*file_name));
+ conflict = true;
+ }
+ }
+ if (conflict)
+ {
+ free (*file_name);
+ *file_name = strdup ("/dev/null");
+ }
+ else
+ {
+ file_names = xnrealloc (file_names, ++file_names_count,
+ sizeof *file_names);
+ file_names[file_names_count-1] = xstrdup (*file_name);
+ }
}
void
void compute_output_file_names (void);
void output_file_names_free (void);
-void output_file_name_check (char const *file_name);
+void output_file_name_check (char **file_name);
FILE *xfopen (const char *name, const char *mode);
void xfclose (FILE *ptr);
#include <configmake.h>
#include <error.h>
#include <get-errno.h>
+#include <pipe.h>
#include <quotearg.h>
-#include <subpipe.h>
#include <timevar.h>
+#include <wait-process.h>
#include "complain.h"
#include "files.h"
assert (i <= ARRAY_CARDINALITY (argv));
}
- init_subpipe ();
- pid = create_subpipe (argv, filter_fd);
+ /* The ugly cast is because gnulib gets the const-ness wrong. */
+ pid = create_pipe_bidi ("m4", m4, (char **)(void*)argv, false, true,
+ true, filter_fd);
free (full_m4sugar);
free (full_m4bison);
free (full_skeleton);
- out = fdopen (filter_fd[0], "w");
+ out = fdopen (filter_fd[1], "w");
if (! out)
error (EXIT_FAILURE, get_errno (),
"fdopen");
/* Read and process m4's output. */
timevar_push (TV_M4);
- end_of_output_subpipe (pid, filter_fd);
- in = fdopen (filter_fd[1], "r");
+ in = fdopen (filter_fd[0], "r");
if (! in)
error (EXIT_FAILURE, get_errno (),
"fdopen");
scan_skel (in);
+ /* scan_skel should have read all of M4's output. Otherwise, when we
+ close the pipe, we risk letting M4 report a broken-pipe to the
+ Bison user. */
+ aver (feof (in));
xfclose (in);
- reap_subpipe (pid, m4);
+ wait_subprocess (pid, "m4", false, false, true, true, NULL);
timevar_pop (TV_M4);
}
"@@" { obstack_1grow (&obstack_for_string, '@'); }
"@{" { obstack_1grow (&obstack_for_string, '['); }
"@}" { obstack_1grow (&obstack_for_string, ']'); }
- "@`" /* Emtpy. Useful for starting an argument
+ "@`" /* Empty. Useful for starting an argument
that begins with whitespace. */
@\n /* Empty. */
yylex_destroy ();
}
-static
-void at_directive_perform (int at_directive_argc,
- char *at_directive_argv[],
- char **outnamep, int *out_linenop)
+static void
+at_directive_perform (int at_directive_argc,
+ char *at_directive_argv[],
+ char **outnamep, int *out_linenop)
{
if (0 == strcmp (at_directive_argv[0], "@basename"))
{
xfclose (yyout);
}
*outnamep = xstrdup (at_directive_argv[1]);
- output_file_name_check (*outnamep);
+ output_file_name_check (outnamep);
yyout = xfopen (*outnamep, "w");
*out_linenop = 1;
}
foo: {};
]])
+[cp ]$1[ expout]
AT_BISON_CHECK([$3 $1], $5, [], [$4])
+AT_CHECK([[cat $1]], [[0]], [expout])
AT_CLEANUP
])
])
AT_CHECK_CONFLICTING_OUTPUT([foo.y], [], [-o foo.y],
-[foo.y: fatal error: refusing to overwrite the input file `foo.y'
+[foo.y: refusing to overwrite the input file `foo.y'
], 1)
]])
AT_CLEANUP
+
+
+## ------------------------------------------------ ##
+## Fatal errors but M4 continues producing output. ##
+## ------------------------------------------------ ##
+
+# At one time, if Bison encountered a fatal error during M4 processing,
+# Bison failed to drain M4's output pipe. The result was a SIGPIPE.
+# On some platforms, the default disposition for SIGPIPE is terminate,
+# which was fine. On others, it's ignore, which caused M4 to report
+# the broken pipe to the user, but we don't want to bother the user with
+# that.
+
+# There is a race condition somewhere. That is, before the associated
+# fix, running this test group many times in a row would occasionally
+# produce a pass among all the failures.
+
+AT_SETUP([[Fatal errors but M4 continues producing output]])
+
+AT_DATA([[gen-skel.pl]],
+[[use warnings;
+use strict;
+my $M4 = "m4";
+my $DNL = "d"."nl";
+print "${M4}_divert_push(0)$DNL\n";
+print '@output(@,@)', "\n";
+(print "garbage"x10, "\n") for (1..1000);
+print "${M4}_divert_pop(0)\n";
+]])
+AT_CHECK([[perl gen-skel.pl > skel.c || exit 77]])
+
+AT_DATA([[input.y]],
+[[%skeleton "./skel.c"
+%%
+start: ;
+]])
+
+AT_BISON_CHECK([[input.y]], [[1]], [[]],
+[[input.y: fatal error: too many arguments for @output directive in skeleton
+]])
+
+AT_CLEANUP