scratch_buffer: use union for internal buffer

Problem reported by Florian Weimer [1] and solution suggested by
Andreas Schwab [2].  It also set the same buffer size independent
of architecture max_align_t size.

Checked on x86_64-linux-gnu and i686-linux-gnu.

	* lib/malloc/scratch_buffer.h (struct scratch_buffer):
	Use an union instead of a max_align_t array for __space,
	so that __space is the same size on all platforms.
	* malloc/scratch_buffer_grow_preserve.c
	(__libc_scratch_buffer_grow_preserve): Likewise.

[1] https://sourceware.org/ml/libc-alpha/2017-09/msg00693.html
[2] https://sourceware.org/ml/libc-alpha/2017-09/msg00695.html

1 files changed, 3 insertions, 3 deletions

diff --git a/include/scratch_buffer.h b/include/scratch_buffer.h
index bb04662eb2..b19b166080 100644
--- a/include/scratch_buffer.h
+++ b/include/scratch_buffer.h
@@ -66,7 +66,7 @@
 struct scratch_buffer {
   void *data;    /* Pointer to the beginning of the scratch area.  */
   size_t length; /* Allocated space at the data pointer, in bytes.  */
-  max_align_t __space[(1023 + sizeof (max_align_t)) / sizeof (max_align_t)];
+  union { max_align_t __align; char __c[1024]; } __space;
 };
 
 /* Initializes *BUFFER so that BUFFER->data points to BUFFER->__space
@@ -74,7 +74,7 @@ struct scratch_buffer {
 static inline void
 scratch_buffer_init (struct scratch_buffer *buffer)
 {
-  buffer->data = buffer->__space;
+  buffer->data = buffer->__space.__c;
   buffer->length = sizeof (buffer->__space);
 }
 
@@ -82,7 +82,7 @@ scratch_buffer_init (struct scratch_buffer *buffer)
 static inline void
 scratch_buffer_free (struct scratch_buffer *buffer)
 {
-  if (buffer->data != buffer->__space)
+  if (buffer->data != buffer->__space.__c)
     free (buffer->data);
 }