getopt: clean up error reporting

getopt can print a whole bunch of error messages, and when used
standalone (from gnulib) it uses fprintf to do that.  But fprintf is a
cancellation point and getopt isn't, and also applying fprintf to a
stream in wide-character mode is not allowed.

glibc has an internal function called __fxprintf that writes a narrow
format string to a stream regardless of mode, but it only handles
ASCII format strings, and it's still a cancellation point.  getopt's
messages are translated, so they might not be ASCII.  So getopt has an
error message to an asprintf buffer, monkeys with internal flag bits
on stderr to disable cancellation, and then calls
__fxprintf(stderr, "%s", buffer).  There isn't even a helper function,
the code is duplicated every time.

This patch fixes __fxprintf to handle arbitrary multibyte format
strings, and adds a variant __fxprintf_nocancel that does the same
thing but also isn't a cancellation point.  (It still _works_ by
monkeying with internal flag bits on the FILE, but that's not really a
layering violation for code in stdio-common.)  All of the #ifdef _LIBC
blocks can then be reduced to their standalone versions with a little
help from some macros at the top of the file.

I also wrote a test case to verify that getopt really isn't a
cancellation point, and I'm glad I did, because it found two bugs, one
of which wasn't even to do with cancellation (see previous patch).

	* stdio-common/fxprintf.c (__fxprintf_nocancel): New function.
	(locked_vfxprintf): New helper function. Handle arbitrary
	multibyte strings, not just ASCII.
	* include/stdio.h: Declare __fxprintf_nocancel.

	* posix/getopt.c: When _LIBC is defined, define fprintf to
	__fxprintf_nocancel, flockfile to _IO_flockfile, and
	funlockfile to _IO_funlockfile.  When neither _LIBC nor
	_POSIX_THREAD_SAFE_FUNCTIONS is defined, define flockfile and
	funlockfile as no-ops.  (_getopt_internal_r): Remove all
	internal #ifdef _LIBC blocks; the standalone error-printing
	code can now be used for libc as well.  Add an
	flockfile/funlockfile pair around one case where the error
	message is printed in several chunks.  Don't use fputc.

	* posix/tst-getopt-cancel.c: New test.
	* posix/Makefile: Run it.

1 files changed, 284 insertions, 0 deletions

diff --git a/posix/tst-getopt-cancel.c b/posix/tst-getopt-cancel.c
new file mode 100644
index 0000000..594596a
--- /dev/null
+++ b/posix/tst-getopt-cancel.c
@@ -0,0 +1,284 @@
+/* Copyright (C) 2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* fprintf is a cancellation point, but getopt is not supposed to be a
+   cancellation point, even when it prints error messages.  */
+
+/* Note: getopt.h must be included first in this file, so we get the
+   GNU getopt rather than the POSIX one.  */
+#include <getopt.h>
+
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <fcntl.h>
+#include <pthread.h>
+#include <unistd.h>
+
+#include <support/support.h>
+#include <support/temp_file.h>
+#include <support/xthread.h>
+
+static bool
+check_stderr (bool expect_errmsg, FILE *stderr_trapped)
+{
+  static char *lineptr = 0;
+  static size_t linesz = 0;
+
+  bool got_errmsg = false;
+  rewind (stderr_trapped);
+  while (getline (&lineptr, &linesz, stderr_trapped) > 0)
+    {
+      got_errmsg = true;
+      fputs (lineptr, stdout);
+    }
+  rewind (stderr_trapped);
+  ftruncate (fileno (stderr_trapped), 0);
+  return got_errmsg == expect_errmsg;
+}
+
+struct test_short
+{
+  const char *label;
+  const char *opts;
+  const char *const argv[8];
+  int argc;
+  bool expect_errmsg;
+};
+
+struct test_long
+{
+  const char *label;
+  const char *opts;
+  const struct option longopts[4];
+  const char *const argv[8];
+  int argc;
+  bool expect_errmsg;
+};
+
+#define DEFINE_TEST_DRIVER(test_type, getopt_call)			\
+  struct test_type##_tdata						\
+  {									\
+    pthread_mutex_t *sync;						\
+    const struct test_type *tcase;					\
+    bool ok;								\
+  };									\
+									\
+  static void *								\
+  test_type##_threadproc (void *data)					\
+  {									\
+    struct test_type##_tdata *tdata = data;				\
+    const struct test_type *tc = tdata->tcase;				\
+									\
+    xpthread_mutex_lock (tdata->sync);					\
+    xpthread_mutex_unlock (tdata->sync);				\
+									\
+    /* At this point, this thread has a cancellation pending.		\
+       We should still be able to get all the way through a getopt	\
+       loop without being cancelled.					\
+       Setting optind to 0 forces getopt to reinitialize itself.  */	\
+    optind = 0;								\
+    opterr = 1;								\
+    optopt = 0;								\
+    while (getopt_call != -1)						\
+      ;									\
+    tdata->ok = true;							\
+									\
+    pthread_testcancel();						\
+    return 0;								\
+  }									\
+									\
+  static bool								\
+  do_##test_type (const struct test_type *tcase, FILE *stderr_trapped)	\
+  {									\
+    pthread_mutex_t sync;						\
+    struct test_type##_tdata tdata;					\
+									\
+    printf("begin: %s\n", tcase->label);				\
+									\
+    xpthread_mutex_init (&sync, 0);					\
+    xpthread_mutex_lock (&sync);					\
+									\
+    tdata.sync = &sync;							\
+    tdata.tcase = tcase;						\
+    tdata.ok = false;							\
+									\
+    pthread_t thr = xpthread_create (0, test_type##_threadproc,		\
+				     (void *)&tdata);			\
+    xpthread_cancel (thr);						\
+    xpthread_mutex_unlock (&sync);					\
+    void *rv = xpthread_join (thr);					\
+									\
+    xpthread_mutex_destroy (&sync);					\
+									\
+    bool ok = true;							\
+    if (!check_stderr (tcase->expect_errmsg, stderr_trapped))		\
+      {									\
+	ok = false;							\
+	printf("FAIL: %s: stderr not as expected\n", tcase->label);	\
+      }									\
+    if (!tdata.ok)							\
+      {									\
+	ok = false;							\
+	printf("FAIL: %s: did not complete loop\n", tcase->label);	\
+      }									\
+    if (rv != PTHREAD_CANCELED)						\
+      {									\
+	ok = false;							\
+	printf("FAIL: %s: thread was not cancelled\n", tcase->label);	\
+      }									\
+    if (ok)								\
+      printf ("pass: %s\n", tcase->label);				\
+    return ok;								\
+  }
+
+DEFINE_TEST_DRIVER (test_short,
+		    getopt (tc->argc, (char *const *)tc->argv, tc->opts))
+DEFINE_TEST_DRIVER (test_long,
+		    getopt_long (tc->argc, (char *const *)tc->argv,
+				 tc->opts, tc->longopts, 0))
+
+/* Caution: all option strings must begin with a '+' or '-' so that
+   getopt does not attempt to permute the argument vector (which is in
+   read-only memory).  */
+const struct test_short tests_short[] = {
+  { "no errors",
+    "+ab:c", { "program", "-ac", "-b", "x", 0 }, 4, false },
+  { "invalid option",
+    "+ab:c", { "program", "-d", 0 },		 2, true },
+  { "missing argument",
+    "+ab:c", { "program", "-b", 0 },		 2, true },
+  { 0 }
+};
+
+const struct test_long tests_long[] = {
+  { "no errors (long)",
+    "+ab:c", { { "alpha",   no_argument,       0, 'a' },
+	       { "bravo",   required_argument, 0, 'b' },
+	       { "charlie", no_argument,       0, 'c' },
+	       { 0 } },
+    { "program", "-a", "--charlie", "--bravo=x", 0 }, 4, false },
+
+  { "invalid option (long)",
+    "+ab:c", { { "alpha",   no_argument,       0, 'a' },
+	       { "bravo",   required_argument, 0, 'b' },
+	       { "charlie", no_argument,       0, 'c' },
+	       { 0 } },
+    { "program", "-a", "--charlie", "--dingo", 0 }, 4, true },
+
+  { "unwanted argument",
+    "+ab:c", { { "alpha",   no_argument,       0, 'a' },
+	       { "bravo",   required_argument, 0, 'b' },
+	       { "charlie", no_argument,       0, 'c' },
+	       { 0 } },
+    { "program", "-a", "--charlie=dingo", "--bravo=x", 0 }, 4, true },
+
+  { "missing argument",
+    "+ab:c", { { "alpha",   no_argument,       0, 'a' },
+	       { "bravo",   required_argument, 0, 'b' },
+	       { "charlie", no_argument,       0, 'c' },
+	       { 0 } },
+    { "program", "-a", "--charlie", "--bravo", 0 }, 4, true },
+
+  { "ambiguous options",
+    "+uvw", { { "veni", no_argument, 0, 'u' },
+	      { "vedi", no_argument, 0, 'v' },
+	      { "veci", no_argument, 0, 'w' } },
+    { "program", "--ve", 0 }, 2, true },
+
+  { "no errors (long W)",
+    "+ab:cW;", { { "alpha",   no_argument,	 0, 'a' },
+		 { "bravo",   required_argument, 0, 'b' },
+		 { "charlie", no_argument,	 0, 'c' },
+		 { 0 } },
+    { "program", "-a", "-W", "charlie", "-W", "bravo=x", 0 }, 6, false },
+
+  { "missing argument (W itself)",
+    "+ab:cW;", { { "alpha",   no_argument,	 0, 'a' },
+		 { "bravo",   required_argument, 0, 'b' },
+		 { "charlie", no_argument,	 0, 'c' },
+		 { 0 } },
+    { "program", "-a", "-W", "charlie", "-W", 0 }, 5, true },
+
+  { "missing argument (W longopt)",
+    "+ab:cW;", { { "alpha",   no_argument,	 0, 'a' },
+		 { "bravo",   required_argument, 0, 'b' },
+		 { "charlie", no_argument,	 0, 'c' },
+		 { 0 } },
+    { "program", "-a", "-W", "charlie", "-W", "bravo", 0 }, 6, true },
+
+  { "unwanted argument (W longopt)",
+    "+ab:cW;", { { "alpha",   no_argument,	 0, 'a' },
+		 { "bravo",   required_argument, 0, 'b' },
+		 { "charlie", no_argument,	 0, 'c' },
+		 { 0 } },
+    { "program", "-a", "-W", "charlie=dingo", "-W", "bravo=x", 0 }, 6, true },
+
+  { "ambiguous options (W)",
+    "+uvwW;", { { "veni", no_argument, 0, 'u' },
+		{ "vedi", no_argument, 0, 'v' },
+		{ "veci", no_argument, 0, 'w' } },
+    { "program", "-W", "ve", 0 }, 3, true },
+
+  { 0 }
+};
+
+static int
+do_test (void)
+{
+  int stderr_trap = create_temp_file ("stderr", 0);
+  if (stderr_trap < 0)
+    {
+      perror ("create_temp_file");
+      return 1;
+    }
+  FILE *stderr_trapped = fdopen(stderr_trap, "r+");
+  if (!stderr_trapped)
+    {
+      perror ("fdopen");
+      return 1;
+    }
+  int old_stderr = dup (fileno (stderr));
+  if (old_stderr < 0)
+    {
+      perror ("dup");
+      return 1;
+    }
+  if (dup2 (stderr_trap, 2) < 0)
+    {
+      perror ("dup2");
+      return 1;
+    }
+  rewind (stderr);
+
+  bool success = true;
+
+  for (const struct test_short *tcase = tests_short; tcase->label; tcase++)
+    success = do_test_short (tcase, stderr_trapped) && success;
+
+  for (const struct test_long *tcase = tests_long; tcase->label; tcase++)
+    success = do_test_long (tcase, stderr_trapped) && success;
+
+  dup2 (old_stderr, 2);
+  close (old_stderr);
+  fclose (stderr_trapped);
+
+  return success ? 0 : 1;
+}
+
+#include <support/test-driver.c>