Implement brk.

1 files changed, 93 insertions, 0 deletions

diff --git a/sysdeps/nacl/brk.c b/sysdeps/nacl/brk.c
new file mode 100644
index 0000000000..b226c216ef
--- /dev/null
+++ b/sysdeps/nacl/brk.c
@@ -0,0 +1,93 @@
+/* brk -- Adjust the "break" at the end of initial data.  NaCl version.
+   Copyright (C) 2013 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 <errno.h>
+#include <libc-internal.h>
+#include <stdint.h>
+#include <sys/mman.h>
+#include <sys/param.h>
+#include <unistd.h>
+
+/* sbrk.c expects this.  */
+void *__curbrk;
+
+static uintptr_t
+page_above (void *addr)
+{
+  return ALIGN_UP ((uintptr_t) addr, EXEC_PAGESIZE);
+}
+
+/* Set the end of the process's data space to ADDR.
+   Return 0 if successful, -1 if not.  */
+int
+__brk (void *addr)
+{
+  /* The NaCl sysbrk call is deprecated, so we do not use it here.  Other
+     libc code expects that __sbrk can be used at least a little bit, so
+     rather than a plain stub we have a minimal __brk implementation here.
+     It just uses mmap/munmap to grow or shrink the break area, punting as
+     soon as mmap fails to use the same contiguous area.  */
+
+  if (__glibc_unlikely (__curbrk == NULL))
+    {
+      /* This is the first call.  We must initialize the record
+         of the current position.  It starts out at the end of the
+         main program's data segment.  */
+
+      /* XXX dynamic case??? */
+      extern char _end[];
+      __curbrk = _end;
+    }
+
+  if (__glibc_unlikely (addr == NULL))
+    /* This is a call just to ensure that __curbrk is set up.  */
+    return 0;
+
+  uintptr_t old_limit = page_above (__curbrk);
+  uintptr_t new_limit = page_above (addr);
+
+  if (old_limit > new_limit)
+    {
+      /* We're shrinking the old heap enough to release some pages.  */
+      if (__munmap ((void *) new_limit, old_limit - new_limit) != 0)
+	return -1;
+    }
+  else if (old_limit < new_limit)
+    {
+      /* We're growing the old heap enough to need some more pages.
+	 See if they are available.  */
+      void *new_space = __mmap ((void *) old_limit, new_limit - old_limit,
+				PROT_READ | PROT_WRITE, MAP_ANON, -1, 0);
+      if (new_space != (void *) old_limit)
+	{
+          if (new_space != MAP_FAILED)
+            {
+              /* mmap chose some different place for the pages
+                 because the contiguous area was not available.
+                 Oh well.  We can't use that.  */
+              __munmap (new_space, new_limit - old_limit);
+              __set_errno (ENOMEM);
+            }
+	  return -1;
+	}
+    }
+
+  __curbrk = addr;
+  return 0;
+}
+weak_alias (__brk, brk)