[glibc/azanella/master-posix_clock] Linux: Use mmap instead of malloc in dirent/tst-getdents64

[Adhemerval Zanella <azanella@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=507f55c05f30c9eb80faf2546ec635c338c039eb

commit 507f55c05f30c9eb80faf2546ec635c338c039eb
Author: Florian Weimer <fweimer@redhat.com>
Date:   Fri Jun 28 10:48:48 2019 +0200

    Linux: Use mmap instead of malloc in dirent/tst-getdents64
    
    malloc dirties the entire allocated memory region due to M_PERTURB
    in the test harness.

Diff:
---
 ChangeLog                                |  6 ++++++
 sysdeps/unix/sysv/linux/tst-getdents64.c | 12 +++++++++---
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index e1d6327..65129ff 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2019-06-28  Florian Weimer  <fweimer@redhat.com>
+
+	* sysdeps/unix/sysv/linux/tst-getdents64.c (large_buffer_checks):
+	Use mmap instead of malloc.  malloc with M_PERTURB writes to the
+	entire allocated memory range.
+
 2019-06-28  Tobias Klauser  <tklauser@distanz.ch>
 
 	* sysdeps/unix/sysv/linux/dl-vdso.h (PREPARE_VERSION): Remove macro.
diff --git a/sysdeps/unix/sysv/linux/tst-getdents64.c b/sysdeps/unix/sysv/linux/tst-getdents64.c
index 24e77e0..8a28e6c 100644
--- a/sysdeps/unix/sysv/linux/tst-getdents64.c
+++ b/sysdeps/unix/sysv/linux/tst-getdents64.c
@@ -27,6 +27,7 @@
 #include <support/check.h>
 #include <support/support.h>
 #include <support/xunistd.h>
+#include <sys/mman.h>
 #include <unistd.h>
 
 /* Called by large_buffer_checks below.  */
@@ -53,8 +54,13 @@ large_buffer_checks (int fd)
   size_t large_buffer_size;
   if (!__builtin_add_overflow (UINT_MAX, 2, &large_buffer_size))
     {
-      char *large_buffer = malloc (large_buffer_size);
-      if (large_buffer == NULL)
+      int flags = MAP_ANONYMOUS | MAP_PRIVATE;
+#ifdef MAP_NORESERVE
+      flags |= MAP_NORESERVE;
+#endif
+      void *large_buffer = mmap (NULL, large_buffer_size,
+                                 PROT_READ | PROT_WRITE, flags, -1, 0);
+      if (large_buffer == MAP_FAILED)
         printf ("warning: could not allocate %zu bytes of memory,"
                 " subtests skipped\n", large_buffer_size);
       else
@@ -65,8 +71,8 @@ large_buffer_checks (int fd)
           large_buffer_check (fd, large_buffer, UINT_MAX);
           large_buffer_check (fd, large_buffer, (size_t) UINT_MAX + 1);
           large_buffer_check (fd, large_buffer, (size_t) UINT_MAX + 2);
+          xmunmap (large_buffer, large_buffer_size);
         }
-      free (large_buffer);
     }
 }