libio: Add new test tst-vtables

Message ID E1fVHBq-0000rg-DX@mid.deneb.enyo.de
State New
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  • libio: Add new test tst-vtables
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Commit Message

Florian Weimer June 19, 2018, 2 p.m.
2018-06-19  Florian Weimer  <fweimer@redhat.com>

	* libio/tst-vtables.c: New file.
	* libio/Makefile (tests-internal): Add tst-vtables.

Comments

Florian Weimer June 26, 2018, 10:37 a.m. | #1
Here is what I committed.

Florian
Subject: [PATCH COMMITTED] libio: Add tst-vtables, tst-vtables-interposed
To: libc-alpha@sourceware.org

2018-06-26  Florian Weimer  <fweimer@redhat.com>

	* libio/Makefile (tests-internal): Add tst-vtables,
	tst-vtables-interposed.
	* libio/tst-vtables.c: New file.
	* libio/tst-vtables-common.c: Likewise.
	* libio/tst-vtables-interposed.c: Likewise.

diff --git a/libio/Makefile b/libio/Makefile
index cbe14a8e25..64d283e512 100644
--- a/libio/Makefile
+++ b/libio/Makefile
@@ -66,6 +66,8 @@ tests = tst_swprintf tst_wprintf tst_swscanf tst_wscanf tst_getwc tst_putwc   \
 	tst-fwrite-error tst-ftell-partial-wide tst-ftell-active-handler \
 	tst-ftell-append tst-fputws tst-bz22415 tst-fgetc-after-eof
 
+tests-internal = tst-vtables tst-vtables-interposed
+
 ifeq (yes,$(build-shared))
 # Add test-fopenloc only if shared library is enabled since it depends on
 # shared localedata objects.
diff --git a/libio/tst-vtables-common.c b/libio/tst-vtables-common.c
new file mode 100644
index 0000000000..5e31012069
--- /dev/null
+++ b/libio/tst-vtables-common.c
@@ -0,0 +1,513 @@
+/* Test for libio vtables and their validation.  Common code.
+   Copyright (C) 2018 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/>.  */
+
+/* This test provides some coverage for how various stdio functions
+   use the vtables in FILE * objects.  The focus is mostly on which
+   functions call which methods, not so much on validating data
+   processing.  An initial series of tests check that custom vtables
+   do not work without activation through _IO_init.
+
+   Note: libio vtables are deprecated feature.  Do not use this test
+   as a documentation source for writing custom vtables.  See
+   fopencookie for a different way of creating custom stdio
+   streams.  */
+
+#include <stdbool.h>
+#include <string.h>
+#include <support/capture_subprocess.h>
+#include <support/check.h>
+#include <support/namespace.h>
+#include <support/support.h>
+#include <support/test-driver.h>
+#include <support/xunistd.h>
+
+#include "libioP.h"
+
+/* Data shared between the test subprocess and the test driver in the
+   parent.  Note that *shared is reset at the start of the check_call
+   function.  */
+struct shared
+{
+  /* Expected file pointer for method calls.  */
+  FILE *fp;
+
+  /* If true, assume that a call to _IO_init is needed to enable
+     custom vtables.  */
+  bool initially_disabled;
+
+  /* Requested return value for the methods which have one.  */
+  int return_value;
+
+  /* A value (usually a character) recorded by some of the methods
+     below.  */
+  int value;
+
+  /* Likewise, for some data.  */
+  char buffer[16];
+  size_t buffer_length;
+
+  /* Total number of method calls.  */
+  unsigned int calls;
+
+  /* Individual method call counts.  */
+  unsigned int calls_finish;
+  unsigned int calls_overflow;
+  unsigned int calls_underflow;
+  unsigned int calls_uflow;
+  unsigned int calls_pbackfail;
+  unsigned int calls_xsputn;
+  unsigned int calls_xsgetn;
+  unsigned int calls_seekoff;
+  unsigned int calls_seekpos;
+  unsigned int calls_setbuf;
+  unsigned int calls_sync;
+  unsigned int calls_doallocate;
+  unsigned int calls_read;
+  unsigned int calls_write;
+  unsigned int calls_seek;
+  unsigned int calls_close;
+  unsigned int calls_stat;
+  unsigned int calls_showmanyc;
+  unsigned int calls_imbue;
+} *shared;
+
+/* Method implementations which increment the counters in *shared.  */
+
+static void
+log_method (FILE *fp, const char *name)
+{
+  if (test_verbose > 0)
+    printf ("info: %s (%p) called\n", name, fp);
+}
+
+static void
+method_finish (FILE *fp, int dummy)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_finish;
+}
+
+static int
+method_overflow (FILE *fp, int ch)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_overflow;
+  shared->value = ch;
+  return shared->return_value;
+}
+
+static int
+method_underflow (FILE *fp)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_underflow;
+  return shared->return_value;
+}
+
+static int
+method_uflow (FILE *fp)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_uflow;
+  return shared->return_value;
+}
+
+static int
+method_pbackfail (FILE *fp, int ch)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_pbackfail;
+  shared->value = ch;
+  return shared->return_value;
+}
+
+static size_t
+method_xsputn (FILE *fp, const void *data, size_t n)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_xsputn;
+
+  size_t to_copy = n;
+  if (n > sizeof (shared->buffer))
+    to_copy = sizeof (shared->buffer);
+  memcpy (shared->buffer, data, to_copy);
+  shared->buffer_length = to_copy;
+  return to_copy;
+}
+
+static size_t
+method_xsgetn (FILE *fp, void *data, size_t n)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_xsgetn;
+  return 0;
+}
+
+static off64_t
+method_seekoff (FILE *fp, off64_t offset, int dir, int mode)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_seekoff;
+  return shared->return_value;
+}
+
+static off64_t
+method_seekpos (FILE *fp, off64_t offset, int mode)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_seekpos;
+  return shared->return_value;
+}
+
+static FILE *
+method_setbuf (FILE *fp, char *buffer, ssize_t length)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_setbuf;
+  return fp;
+}
+
+static int
+method_sync (FILE *fp)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_sync;
+  return shared->return_value;
+}
+
+static int
+method_doallocate (FILE *fp)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_doallocate;
+  return shared->return_value;
+}
+
+static ssize_t
+method_read (FILE *fp, void *data, ssize_t length)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_read;
+  return shared->return_value;
+}
+
+static ssize_t
+method_write (FILE *fp, const void *data, ssize_t length)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_write;
+  return shared->return_value;
+}
+
+static off64_t
+method_seek (FILE *fp, off64_t offset, int mode)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_seek;
+  return shared->return_value;
+}
+
+static int
+method_close (FILE *fp)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_close;
+  return shared->return_value;
+}
+
+static int
+method_stat (FILE *fp, void *buffer)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_stat;
+  return shared->return_value;
+}
+
+static int
+method_showmanyc (FILE *fp)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_showmanyc;
+  return shared->return_value;
+}
+
+static void
+method_imbue (FILE *fp, void *locale)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_imbue;
+}
+
+/* Our custom vtable.  */
+
+static const struct _IO_jump_t jumps =
+{
+  JUMP_INIT_DUMMY,
+  JUMP_INIT (finish, method_finish),
+  JUMP_INIT (overflow, method_overflow),
+  JUMP_INIT (underflow, method_underflow),
+  JUMP_INIT (uflow, method_uflow),
+  JUMP_INIT (pbackfail, method_pbackfail),
+  JUMP_INIT (xsputn, method_xsputn),
+  JUMP_INIT (xsgetn, method_xsgetn),
+  JUMP_INIT (seekoff, method_seekoff),
+  JUMP_INIT (seekpos, method_seekpos),
+  JUMP_INIT (setbuf, method_setbuf),
+  JUMP_INIT (sync, method_sync),
+  JUMP_INIT (doallocate, method_doallocate),
+  JUMP_INIT (read, method_read),
+  JUMP_INIT (write, method_write),
+  JUMP_INIT (seek, method_seek),
+  JUMP_INIT (close, method_close),
+  JUMP_INIT (stat, method_stat),
+  JUMP_INIT (showmanyc, method_showmanyc),
+  JUMP_INIT (imbue, method_imbue)
+};
+
+/* Our file implementation.  */
+
+struct my_file
+{
+  FILE f;
+  const struct _IO_jump_t *vtable;
+};
+
+struct my_file
+my_file_create (void)
+{
+  return (struct my_file)
+    {
+      /* Disable locking, so that we do not have to set up a lock
+         pointer.  */
+      .f._flags =  _IO_USER_LOCK,
+
+      /* Copy the offset from the an initialized handle, instead of
+         figuring it out from scratch.  */
+      .f._vtable_offset = stdin->_vtable_offset,
+
+      .vtable = &jumps,
+    };
+}
+
+/* Initial tests which do not enable vtable compatibility.  */
+
+/* Inhibit GCC optimization of fprintf.  */
+typedef int (*fprintf_type) (FILE *, const char *, ...);
+static const volatile fprintf_type fprintf_ptr = &fprintf;
+
+static void
+without_compatibility_fprintf (void *closure)
+{
+  /* This call should abort.  */
+  fprintf_ptr (shared->fp, " ");
+  _exit (1);
+}
+
+static void
+without_compatibility_fputc (void *closure)
+{
+  /* This call should abort.  */
+  fputc (' ', shared->fp);
+  _exit (1);
+}
+
+static void
+without_compatibility_fgetc (void *closure)
+{
+  /* This call should abort.  */
+  fgetc (shared->fp);
+  _exit (1);
+}
+
+static void
+without_compatibility_fflush (void *closure)
+{
+  /* This call should abort.  */
+  fflush (shared->fp);
+  _exit (1);
+}
+
+/* Exit status after abnormal termination.  */
+static int termination_status;
+
+static void
+init_termination_status (void)
+{
+  pid_t pid = xfork ();
+  if (pid == 0)
+    abort ();
+  xwaitpid (pid, &termination_status, 0);
+
+  TEST_VERIFY (WIFSIGNALED (termination_status));
+  TEST_COMPARE (WTERMSIG (termination_status), SIGABRT);
+}
+
+static void
+check_for_termination (const char *name, void (*callback) (void *))
+{
+  struct my_file file = my_file_create ();
+  shared->fp = &file.f;
+  shared->return_value = -1;
+  shared->calls = 0;
+  struct support_capture_subprocess proc
+    = support_capture_subprocess (callback, NULL);
+  support_capture_subprocess_check (&proc, name, termination_status,
+                                    sc_allow_stderr);
+  const char *message
+    = "Fatal error: glibc detected an invalid stdio handle\n";
+  TEST_COMPARE_BLOB (proc.err.buffer, proc.err.length,
+                     message, strlen (message));
+  TEST_COMPARE (shared->calls, 0);
+  support_capture_subprocess_free (&proc);
+}
+
+/* The test with vtable validation disabled.  */
+
+/* This function does not have a prototype in libioP.h to prevent
+   accidental use from within the library (which would disable vtable
+   verification).  */
+void _IO_init (FILE *fp, int flags);
+
+static void
+with_compatibility_fprintf (void *closure)
+{
+  TEST_COMPARE (fprintf_ptr (shared->fp, "A%sCD", "B"), 4);
+  TEST_COMPARE (shared->calls, 3);
+  TEST_COMPARE (shared->calls_xsputn, 3);
+  TEST_COMPARE_BLOB (shared->buffer, shared->buffer_length,
+                     "CD", 2);
+}
+
+static void
+with_compatibility_fputc (void *closure)
+{
+  shared->return_value = '@';
+  TEST_COMPARE (fputc ('@', shared->fp), '@');
+  TEST_COMPARE (shared->calls, 1);
+  TEST_COMPARE (shared->calls_overflow, 1);
+  TEST_COMPARE (shared->value, '@');
+}
+
+static void
+with_compatibility_fgetc (void *closure)
+{
+  shared->return_value = 'X';
+  TEST_COMPARE (fgetc (shared->fp), 'X');
+  TEST_COMPARE (shared->calls, 1);
+  TEST_COMPARE (shared->calls_uflow, 1);
+}
+
+static void
+with_compatibility_fflush (void *closure)
+{
+  TEST_COMPARE (fflush (shared->fp), 0);
+  TEST_COMPARE (shared->calls, 1);
+  TEST_COMPARE (shared->calls_sync, 1);
+}
+
+/* Call CALLBACK in a subprocess, after setting up a custom file
+   object and updating shared->fp.  */
+static void
+check_call (const char *name, void (*callback) (void *),
+            bool initially_disabled)
+{
+  *shared = (struct shared)
+    {
+     .initially_disabled = initially_disabled,
+    };
+
+  /* Set up a custom file object.  */
+  struct my_file file = my_file_create ();
+  shared->fp = &file.f;
+  if (shared->initially_disabled)
+    _IO_init (shared->fp, file.f._flags);
+
+  if (test_verbose > 0)
+    printf ("info: calling test %s\n", name);
+  support_isolate_in_subprocess (callback, NULL);
+}
+
+/* Run the tests.  INITIALLY_DISABLED indicates whether custom vtables
+   are disabled when the test starts.  */
+static int
+run_tests (bool initially_disabled)
+{
+  /* The test relies on fatal error messages being printed to standard
+     error.  */
+  setenv ("LIBC_FATAL_STDERR_", "1", 1);
+
+  shared = support_shared_allocate (sizeof (*shared));
+  shared->initially_disabled = initially_disabled;
+  init_termination_status ();
+
+  if (initially_disabled)
+    {
+      check_for_termination ("fprintf", without_compatibility_fprintf);
+      check_for_termination ("fputc", without_compatibility_fputc);
+      check_for_termination ("fgetc", without_compatibility_fgetc);
+      check_for_termination ("fflush", without_compatibility_fflush);
+    }
+
+  check_call ("fprintf", with_compatibility_fprintf, initially_disabled);
+  check_call ("fputc", with_compatibility_fputc, initially_disabled);
+  check_call ("fgetc", with_compatibility_fgetc, initially_disabled);
+  check_call ("fflush", with_compatibility_fflush, initially_disabled);
+
+  support_shared_free (shared);
+  shared = NULL;
+
+  return 0;
+}
diff --git a/libio/tst-vtables-interposed.c b/libio/tst-vtables-interposed.c
new file mode 100644
index 0000000000..aaa5a84e0a
--- /dev/null
+++ b/libio/tst-vtables-interposed.c
@@ -0,0 +1,36 @@
+/* Test for libio vtables and their validation.  Enabled through interposition.
+   Copyright (C) 2018 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/>.  */
+
+#include "tst-vtables-common.c"
+
+/* Provide an interposed definition of the standard file handles with
+   our own vtable.  stdout/stdin/stderr will not work as a result, but
+   a succesful test does not print anything, so this is fine.  */
+#define _IO_file_jumps jumps
+#include "stdfiles.c"
+
+static int
+do_test (void)
+{
+  return run_tests (false);
+}
+
+/* Calling setvbuf in the test driver is not supported with our
+   interposed file handles.  */
+#define TEST_NO_SETVBUF
+#include <support/test-driver.c>
diff --git a/libio/tst-vtables.c b/libio/tst-vtables.c
new file mode 100644
index 0000000000..c31a552f61
--- /dev/null
+++ b/libio/tst-vtables.c
@@ -0,0 +1,27 @@
+/* Test for libio vtables and their validation.  Initially disabled case.
+   Copyright (C) 2018 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/>.  */
+
+#include "tst-vtables-common.c"
+
+static int
+do_test (void)
+{
+  return run_tests (true);
+}
+
+#include <support/test-driver.c>

Patch

diff --git a/libio/Makefile b/libio/Makefile
index cbe14a8e25..b2c4d151f5 100644
--- a/libio/Makefile
+++ b/libio/Makefile
@@ -66,6 +66,8 @@  tests = tst_swprintf tst_wprintf tst_swscanf tst_wscanf tst_getwc tst_putwc   \
 	tst-fwrite-error tst-ftell-partial-wide tst-ftell-active-handler \
 	tst-ftell-append tst-fputws tst-bz22415 tst-fgetc-after-eof
 
+tests-internal = tst-vtables
+
 ifeq (yes,$(build-shared))
 # Add test-fopenloc only if shared library is enabled since it depends on
 # shared localedata objects.
diff --git a/libio/tst-vtables.c b/libio/tst-vtables.c
new file mode 100644
index 0000000000..421b39240f
--- /dev/null
+++ b/libio/tst-vtables.c
@@ -0,0 +1,498 @@ 
+/* Test for libio vtables and their validation.
+   Copyright (C) 2018 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/>.  */
+
+/* This test provides some coverage for how various stdio functions
+   use the vtables in FILE * objects.  The focus is mostly on which
+   functions call which methods, not so much on validating data
+   processing.  An initial series of tests check that custom vtables
+   do not work without activation through _IO_init.
+
+   Note: libio vtables are deprecated feature.  Do not use this test
+   as a documentation source for writing custom vtables.  See
+   fopencookie for a different way of creating custom stdio
+   streams.  */
+
+#include <string.h>
+#include <support/capture_subprocess.h>
+#include <support/check.h>
+#include <support/namespace.h>
+#include <support/support.h>
+#include <support/test-driver.h>
+#include <support/xunistd.h>
+
+#include "libioP.h"
+
+/* Data shared between the test subprocess and the test driver in the
+   parent.  */
+struct shared
+{
+  /* Expected file pointer for method calls.  */
+  FILE *fp;
+
+  /* Requested return value for the methods which have one.  */
+  int return_value;
+
+  /* A value (usually a character) recorded by some of the methods
+     below.  */
+  int value;
+
+  /* Likewise, for some data.  */
+  char buffer[16];
+  size_t buffer_length;
+
+  /* Total number of method calls.  */
+  unsigned int calls;
+
+  /* Individual method call counts.  */
+  unsigned int calls_finish;
+  unsigned int calls_overflow;
+  unsigned int calls_underflow;
+  unsigned int calls_uflow;
+  unsigned int calls_pbackfail;
+  unsigned int calls_xsputn;
+  unsigned int calls_xsgetn;
+  unsigned int calls_seekoff;
+  unsigned int calls_seekpos;
+  unsigned int calls_setbuf;
+  unsigned int calls_sync;
+  unsigned int calls_doallocate;
+  unsigned int calls_read;
+  unsigned int calls_write;
+  unsigned int calls_seek;
+  unsigned int calls_close;
+  unsigned int calls_stat;
+  unsigned int calls_showmanyc;
+  unsigned int calls_imbue;
+} *shared;
+
+/* Method implementations which increment the counters in *shared.  */
+
+static void
+log_method (FILE *fp, const char *name)
+{
+  if (test_verbose > 0)
+    printf ("info: %s (%p) called\n", name, fp);
+}
+
+static void
+method_finish (FILE *fp, int dummy)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_finish;
+}
+
+static int
+method_overflow (FILE *fp, int ch)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_overflow;
+  shared->value = ch;
+  return shared->return_value;
+}
+
+static int
+method_underflow (FILE *fp)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_underflow;
+  return shared->return_value;
+}
+
+static int
+method_uflow (FILE *fp)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_uflow;
+  return shared->return_value;
+}
+
+static int
+method_pbackfail (FILE *fp, int ch)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_pbackfail;
+  shared->value = ch;
+  return shared->return_value;
+}
+
+static size_t
+method_xsputn (FILE *fp, const void *data, size_t n)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_xsputn;
+
+  size_t to_copy = n;
+  if (n > sizeof (shared->buffer))
+    to_copy = sizeof (shared->buffer);
+  memcpy (shared->buffer, data, to_copy);
+  shared->buffer_length = to_copy;
+  return to_copy;
+}
+
+static size_t
+method_xsgetn (FILE *fp, void *data, size_t n)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_xsgetn;
+  return 0;
+}
+
+static off64_t
+method_seekoff (FILE *fp, off64_t offset, int dir, int mode)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_seekoff;
+  return shared->return_value;
+}
+
+static off64_t
+method_seekpos (FILE *fp, off64_t offset, int mode)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_seekpos;
+  return shared->return_value;
+}
+
+static FILE *
+method_setbuf (FILE *fp, char *buffer, ssize_t length)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_setbuf;
+  return fp;
+}
+
+static int
+method_sync (FILE *fp)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_sync;
+  return shared->return_value;
+}
+
+static int
+method_doallocate (FILE *fp)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_doallocate;
+  return shared->return_value;
+}
+
+static ssize_t
+method_read (FILE *fp, void *data, ssize_t length)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_read;
+  return shared->return_value;
+}
+
+static ssize_t
+method_write (FILE *fp, const void *data, ssize_t length)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_write;
+  return shared->return_value;
+}
+
+static ssize_t
+method_seek (FILE *fp, off64_t offset, int mode)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_seek;
+  return shared->return_value;
+}
+
+static int
+method_close (FILE *fp)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_close;
+  return shared->return_value;
+}
+
+static int
+method_stat (FILE *fp, void *buffer)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_stat;
+  return shared->return_value;
+}
+
+static int
+method_showmanyc (FILE *fp)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_showmanyc;
+  return shared->return_value;
+}
+
+static void
+method_imbue (FILE *fp, void *locale)
+{
+  log_method (fp, __func__);
+  TEST_VERIFY (fp == shared->fp);
+  ++shared->calls;
+  ++shared->calls_imbue;
+}
+
+/* Our custom vtable.  */
+
+static const struct _IO_jump_t jumps =
+{
+  JUMP_INIT_DUMMY,
+  JUMP_INIT (finish, method_finish),
+  JUMP_INIT (overflow, method_overflow),
+  JUMP_INIT (underflow, method_underflow),
+  JUMP_INIT (uflow, method_uflow),
+  JUMP_INIT (pbackfail, method_pbackfail),
+  JUMP_INIT (xsputn, method_xsputn),
+  JUMP_INIT (xsgetn, method_xsgetn),
+  JUMP_INIT (seekoff, method_seekoff),
+  JUMP_INIT (seekpos, method_seekpos),
+  JUMP_INIT (setbuf, method_setbuf),
+  JUMP_INIT (sync, method_sync),
+  JUMP_INIT (doallocate, method_doallocate),
+  JUMP_INIT (read, method_read),
+  JUMP_INIT (write, method_write),
+  JUMP_INIT (seek, method_seek),
+  JUMP_INIT (close, method_close),
+  JUMP_INIT (stat, method_stat),
+  JUMP_INIT (showmanyc, method_showmanyc),
+  JUMP_INIT (imbue, method_imbue)
+};
+
+/* Our file implementation.  */
+
+struct my_file
+{
+  FILE f;
+  const struct _IO_jump_t *vtable;
+};
+
+struct my_file
+my_file_create (void)
+{
+  return (struct my_file)
+    {
+      /* Disable locking, so that we do not have to set up a lock
+         pointer.  */
+      .f._flags =  _IO_USER_LOCK,
+
+      /* Copy the offset from the an initialized handle, instead of
+         figuring it out from scratch.  */
+      .f._vtable_offset = stdin->_vtable_offset,
+
+      .vtable = &jumps,
+    };
+}
+
+/* Initial tests which do not enable vtable compatibility.  */
+
+/* Inhibit GCC optimization of fprintf.  */
+typedef int (*fprintf_type) (FILE *, const char *, ...);
+static const volatile fprintf_type fprintf_ptr = &fprintf;
+
+static void
+without_compatibility_fprintf (void *closure)
+{
+  /* This call should abort.  */
+  fprintf_ptr (shared->fp, " ");
+  _exit (1);
+}
+
+static void
+without_compatibility_fputc (void *closure)
+{
+  /* This call should abort.  */
+  fputc (' ', shared->fp);
+  _exit (1);
+}
+
+static void
+without_compatibility_fgetc (void *closure)
+{
+  /* This call should abort.  */
+  fgetc (shared->fp);
+  _exit (1);
+}
+
+static void
+without_compatibility_fflush (void *closure)
+{
+  /* This call should abort.  */
+  fflush (shared->fp);
+  _exit (1);
+}
+
+/* Exit status after abnormal termination.  */
+static int termination_status;
+
+static void
+init_termination_status (void)
+{
+  pid_t pid = xfork ();
+  if (pid == 0)
+    abort ();
+  xwaitpid (pid, &termination_status, 0);
+
+  TEST_VERIFY (WIFSIGNALED (termination_status));
+  TEST_COMPARE (WTERMSIG (termination_status), SIGABRT);
+}
+
+static void
+check_for_termination (const char *name, void (*callback) (void *))
+{
+  struct my_file file = my_file_create ();
+  shared->fp = &file.f;
+  shared->return_value = -1;
+  shared->calls = 0;
+  struct support_capture_subprocess proc
+    = support_capture_subprocess (callback, NULL);
+  support_capture_subprocess_check (&proc, name, termination_status,
+                                    sc_allow_stderr);
+  const char *message
+    = "Fatal error: glibc detected an invalid stdio handle\n";
+  TEST_COMPARE_BLOB (proc.err.buffer, proc.err.length,
+                     message, strlen (message));
+  TEST_COMPARE (shared->calls, 0);
+  support_capture_subprocess_free (&proc);
+}
+
+/* The test with vtable validation disabled.  */
+
+/* This function does not have a prototype in libioP.h to prevent
+   accidental use from within the library (which would disable vtable
+   verification).  */
+void _IO_init (FILE *fp, int flags);
+
+static void
+with_compatibility_fprintf (void *closure)
+{
+  TEST_COMPARE (fprintf_ptr (shared->fp, "A%sCD", "B"), 4);
+  TEST_COMPARE (shared->calls, 3);
+  TEST_COMPARE (shared->calls_xsputn, 3);
+  TEST_COMPARE_BLOB (shared->buffer, shared->buffer_length,
+                     "CD", 2);
+}
+
+static void
+with_compatibility_fputc (void *closure)
+{
+  shared->return_value = '@';
+  TEST_COMPARE (fputc ('@', shared->fp), '@');
+  TEST_COMPARE (shared->calls, 1);
+  TEST_COMPARE (shared->calls_overflow, 1);
+  TEST_COMPARE (shared->value, '@');
+}
+
+static void
+with_compatibility_fgetc (void *closure)
+{
+  shared->return_value = 'X';
+  TEST_COMPARE (fgetc (shared->fp), 'X');
+  TEST_COMPARE (shared->calls, 1);
+  TEST_COMPARE (shared->calls_uflow, 1);
+}
+
+static void
+with_compatibility_fflush (void *closure)
+{
+  TEST_COMPARE (fflush (shared->fp), 0);
+  TEST_COMPARE (shared->calls, 1);
+  TEST_COMPARE (shared->calls_sync, 1);
+}
+
+/* Call CALLBACK in a subprocess, after setting up a custom file
+   object and updating shared->fp.  */
+static void
+check_call (const char *name, void (*callback) (void *))
+{
+  *shared = (struct shared) { };
+
+  /* Set up a custom file object.  */
+  struct my_file file = my_file_create ();
+  shared->fp = &file.f;
+  _IO_init (shared->fp, file.f._flags);
+
+  if (test_verbose > 0)
+    printf ("info: calling test %s\n", name);
+  support_isolate_in_subprocess (callback, NULL);
+}
+
+static int
+do_test (void)
+{
+  /* The test relies on fatal error messages being printed to standard
+     error.  */
+  setenv ("LIBC_FATAL_STDERR_", "1", 1);
+
+  shared = support_shared_allocate (sizeof (*shared));
+  init_termination_status ();
+
+  check_for_termination ("fprintf", without_compatibility_fprintf);
+  check_for_termination ("fputc", without_compatibility_fputc);
+  check_for_termination ("fgetc", without_compatibility_fgetc);
+  check_for_termination ("fflush", without_compatibility_fflush);
+
+  check_call ("fprintf", with_compatibility_fprintf);
+  check_call ("fputc", with_compatibility_fputc);
+  check_call ("fgetc", with_compatibility_fgetc);
+  check_call ("fflush", with_compatibility_fflush);
+
+  support_shared_free (shared);
+  shared = NULL;
+
+  return 0;
+}
+
+#include <support/test-driver.c>