X-Git-Url: http://erislabs.net/gitweb/?a=blobdiff_plain;f=lib%2Fopenat-priv.h;h=829cf7d08559fae6b27df5607651df59e9b6512f;hb=25fb29a19d9993a32075b7c3fefa959e3345ab64;hp=e0818731f4506c98d25f6bd153d733fe7adc4e27;hpb=b2e2010c7c902235b5efb5bd3c6529f61b093aa4;p=gnulib.git

diff --git a/lib/openat-priv.h b/lib/openat-priv.h
index e0818731f..829cf7d08 100644
--- a/lib/openat-priv.h
+++ b/lib/openat-priv.h
@@ -1,6 +1,6 @@
 /* Internals for openat-like functions.
 
-   Copyright (C) 2005-2006, 2009-2010 Free Software Foundation, Inc.
+   Copyright (C) 2005-2006, 2009-2013 Free Software Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -21,9 +21,29 @@
 #define _GL_HEADER_OPENAT_PRIV
 
 #include <errno.h>
+#include <limits.h>
 #include <stdlib.h>
 
-#define OPENAT_BUFFER_SIZE 512
+/* Maximum number of bytes that it is safe to allocate as a single
+   array on the stack, and that is known as a compile-time constant.
+   The assumption is that we'll touch the array very quickly, or a
+   temporary very near the array, provoking an out-of-memory trap.  On
+   some operating systems, there is only one guard page for the stack,
+   and a page size can be as small as 4096 bytes.  Subtract 64 in the
+   hope that this will let the compiler touch a nearby temporary and
+   provoke a trap.  */
+#define SAFER_ALLOCA_MAX (4096 - 64)
+
+#define SAFER_ALLOCA(m) ((m) < SAFER_ALLOCA_MAX ? (m) : SAFER_ALLOCA_MAX)
+
+#if defined PATH_MAX
+# define OPENAT_BUFFER_SIZE SAFER_ALLOCA (PATH_MAX)
+#elif defined _XOPEN_PATH_MAX
+# define OPENAT_BUFFER_SIZE SAFER_ALLOCA (_XOPEN_PATH_MAX)
+#else
+# define OPENAT_BUFFER_SIZE SAFER_ALLOCA (1024)
+#endif
+
 char *openat_proc_name (char buf[OPENAT_BUFFER_SIZE], int fd, char const *file);
 
 /* Trying to access a BUILD_PROC_NAME file will fail on systems without