[PATCH v5] x86: Add a testcase for BZ #29863

["H.J. Lu" <hjl.tools@gmail.com>]

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 | 106 ++++++++++++++++++++++++++++++++++
 2 files changed, 114 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..eefa9e43c4
--- /dev/null
+++ b/sysdeps/x86/tst-memcmp-race.c
@@ -0,0 +1,106 @@
+/* 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	LOOP1		10000
+#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);
+	}
+    }
+  else
+    {
+      size_t offset = a->len > 16 ? a->len - 16 : 1;
+      for (i = 0; i < LOOP2; i++)
+	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 ();
+
+  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