flat: tweak default stack alignment

The recent commit 1f0ce8b ("mm: Move ARCH_SLAB_MINALIGN and
ARCH_KMALLOC_MINALIGN to <linux/slab_def.h>") which moved the
ARCH_SLAB_MINALIGN default into the global header inadvertently broke FLAT
for a bunch of systems.  Blackfin systems now fail on any FLAT exec with:
Unable to read code+data+bss, errno 14 When your /init is a FLAT binary,
obviously this can be annoying ;).

This stems from the alignment usage in the FLAT loader.  The behavior
before was that FLAT would default to ARCH_SLAB_MINALIGN only if it was
defined, and this was only defined by arches when they wanted a larger
alignment value.  Otherwise it'd default to pointer alignment.  Arguably,
this is kind of hokey that the FLAT is semi-abusing defines it shouldn't.

So let's merge the two alignment requirements so the floor is never 0.

Signed-off-by: Mike Frysinger <[email protected]>
Cc: David McCullough <[email protected]>
Cc: Greg Ungerer <[email protected]>
Cc: Paul Mundt <[email protected]>
Cc: Michal Simek <[email protected]>
Cc: Hirokazu Takata <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: David Howells <[email protected]>
Cc: David Woodhouse <[email protected]>
Cc: Pekka Enberg <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: vapier

fs/binfmt_flat.c

@@ -68,11 +68,7 @@
  * Here we can be a bit looser than the data sections since this
  * needs to only meet arch ABI requirements.
  */
-#ifdef ARCH_SLAB_MINALIGN
-#define FLAT_STACK_ALIGN	(ARCH_SLAB_MINALIGN)
-#else
-#define FLAT_STACK_ALIGN	(sizeof(void *))
-#endif
+#define FLAT_STACK_ALIGN	max_t(unsigned long, sizeof(void *), ARCH_SLAB_MINALIGN)
 
 #define RELOC_FAILED 0xff00ff01		/* Relocation incorrect somewhere */
 #define UNLOADED_LIB 0x7ff000ff		/* Placeholder for unused library */