[v3] x86: Add a testcase for BZ #29863

  When a thread is updating the memory area of memcmp and another thread
is doing memcmp, the memcmp return value is undefined.  Add a testcase
to verify that memcmp won't segfault in this case.
---
 sysdeps/x86/Makefile          |   8 +++
 sysdeps/x86/tst-memcmp-race.c | 118 ++++++++++++++++++++++++++++++++++
 2 files changed, 126 insertions(+)
 create mode 100644 sysdeps/x86/tst-memcmp-race.c
  

On Wed, Dec 14, 2022 at 12:03 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> When a thread is updating the memory area of memcmp and another thread
> is doing memcmp, the memcmp return value is undefined.  Add a testcase
> to verify that memcmp won't segfault in this case.
> ---
>  sysdeps/x86/Makefile          |   8 +++
>  sysdeps/x86/tst-memcmp-race.c | 118 ++++++++++++++++++++++++++++++++++
>  2 files changed, 126 insertions(+)
>  create mode 100644 sysdeps/x86/tst-memcmp-race.c
>
> diff --git a/sysdeps/x86/Makefile b/sysdeps/x86/Makefile
> index 56fd5fc805..c3f05a06ab 100644
> --- a/sysdeps/x86/Makefile
> +++ b/sysdeps/x86/Makefile
> @@ -257,3 +257,11 @@ tests += \
>  tests-static += \
>    tst-sysconf-cache-linesize-static
>  endif
> +
> +ifeq ($(subdir),nptl)
> +tests += \
> +  tst-memcmp-race \
> +# tests
> +
> +CFLAGS-tst-memcmp-race.c += -O0
> +endif
> diff --git a/sysdeps/x86/tst-memcmp-race.c b/sysdeps/x86/tst-memcmp-race.c
> new file mode 100644
> index 0000000000..f28b80ef82
> --- /dev/null
> +++ b/sysdeps/x86/tst-memcmp-race.c
> @@ -0,0 +1,118 @@
> +/* Test case for memcmp with race condition.
> +   Copyright (C) 2022 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
> +   <https://www.gnu.org/licenses/>.  */
> +
> +/* Verify that there is no segfault when one thread is updating the
> +   memory block of memcmp and the other thread is doing memcmp.  */
> +
> +#define TEST_MAIN
> +#define TEST_NAME "memcmp"
> +
> +#include <stdio.h>
> +#include <stdint.h>
> +#include <string.h>
> +#include <string/test-string.h>
> +#include <support/xthread.h>
> +
> +#define        NUM_THREADS     2
> +#define        STR             "abcdefghijklmnopq"

not needed.

> +#define        LOOP1           100

The test is relatively fast, this value can probably be increased
a bit.
> +#define        LOOP2           1000000
> +
> +typedef int (*proto_t) (const void *, const void *, size_t);
> +
> +IMPL (memcmp, 1)
> +
> +struct arg
> +{
> +  proto_t func;
> +  size_t len;
> +  int i;
> +};
> +
> +static void *
> +childThread (void *tArgs)
> +{
> +  struct arg *a = (struct arg *) tArgs;
> +  int i;
> +
> +  if (0 == a->i % 2)
> +    {
> +      for (i = 0; i < LOOP1; i++)
> +       {
> +         int result = a->func (buf1, buf2, a->len);
> +         printf ("i = %d : result = %d\n", i, result);
remove print, make `result` volatile.
> +       }
> +    }
> +  else
> +    {
> +      size_t offset = a->len > 16 ? a->len - 16 : 1;
> +      for (i = 0; i < LOOP2; i++)
> +       buf1[offset] = (0 == (i % 2)) ? 'b' : 'c';
buf1[offset] = (i & 1);
> +    }
> +
> +  return NULL;
> +}
> +
> +static void
> +do_one_test (proto_t func, size_t len)
> +{
> +  int i;
> +  pthread_t threads[NUM_THREADS];
> +  struct arg a[NUM_THREADS];
> +
> +  for (i = 0; i < NUM_THREADS; ++i)
> +    {
> +      a[i].func = func;
> +      a[i].len = len;
> +      a[i].i = i;
> +      threads[i] = xpthread_create (NULL, childThread, (void *)&a[i]);
> +    }
> +
> +  for (i = 0; i < NUM_THREADS; ++i)
> +    xpthread_join (threads[i]);
> +}
> +
> +int
> +test_main (void)
> +{
> +  test_init ();
> +
> +  size_t remain = page_size;
> +  size_t offset = 0;
> +  do
> +    {
> +      size_t len = sizeof STR - 1;
> +      if (len > remain)
> +       len = remain;
> +      memcpy (buf1 + offset, STR, len);
> +      memcpy (buf2 + offset, STR, len);
> +      offset += len;
> +      remain -= len;
> +    }
> +  while (remain > 0);
remove.

memset(buf1, 1, page_size);
memset(buf2, 1, page_size);
> +
> +  for (size_t i = 0; i <= 11; i++)
> +    {
> +      FOR_EACH_IMPL (impl, 0)
> +       do_one_test ((proto_t) impl->fn, (1 << i) + 1);
> +    }
> +
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>
> --
> 2.38.1
>