i386: Increase MALLOC_ALIGNMENT to 16 [BZ #21120]

GCC 7 changed the definition of max_align_t on i386:

https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=9b5c49ef97e63cc63f1ffa13baf771368105ebe2

As a result, glibc malloc no longer returns memory blocks which are as
aligned as max_align_t requires.

This causes malloc/tst-malloc-thread-fail to fail with an error like this
one:

error: allocation function 0, size 144 not aligned to 16

This patch moves the MALLOC_ALIGNMENT definition to <malloc-alignment.h>
and increases the malloc alignment to 16 for i386.

	[BZ #21120]
	* malloc/malloc-internal.h (MALLOC_ALIGNMENT): Moved to ...
	* sysdeps/generic/malloc-alignment.h: Here.  New file.
	* sysdeps/i386/malloc-alignment.h: Likewise.
	* sysdeps/generic/malloc-machine.h: Include <malloc-alignment.h>.

2 files changed, 32 insertions, 0 deletions

diff --git a/sysdeps/generic/malloc-alignment.h b/sysdeps/generic/malloc-alignment.h
new file mode 100644
index 0000000..efd03fa
--- /dev/null
+++ b/sysdeps/generic/malloc-alignment.h
@@ -0,0 +1,31 @@
+/* Define MALLOC_ALIGNMENT for malloc.  Generic version.
+   Copyright (C) 2017 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/>.  */
+
+#ifndef _GENERIC_MALLOC_ALIGNMENT_H
+#define _GENERIC_MALLOC_ALIGNMENT_H
+
+/* MALLOC_ALIGNMENT is the minimum alignment for malloc'ed chunks.  It
+   must be a power of two at least 2 * SIZE_SZ, even on machines for
+   which smaller alignments would suffice. It may be defined as larger
+   than this though. Note however that code and data structures are
+   optimized for the case of 8-byte alignment.  */
+#define MALLOC_ALIGNMENT (2 * SIZE_SZ < __alignof__ (long double) \
+			  ? __alignof__ (long double) : 2 * SIZE_SZ)
+
+
+#endif /* !defined(_GENERIC_MALLOC_ALIGNMENT_H) */
diff --git a/sysdeps/generic/malloc-machine.h b/sysdeps/generic/malloc-machine.h
index 21aa9fc..4491b90 100644
--- a/sysdeps/generic/malloc-machine.h
+++ b/sysdeps/generic/malloc-machine.h
@@ -21,6 +21,7 @@
 #define _GENERIC_MALLOC_MACHINE_H
 
 #include <atomic.h>
+#include <malloc-alignment.h>
 
 #ifndef atomic_full_barrier
 # define atomic_full_barrier() __asm ("" ::: "memory")