btrfs-tools: debian/patches/09-unaligned-memaccess.patch

btrfs-tools: debian/patches/09-unaligned-memaccess.patch

[Holger Fischer]

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Dear BTRFS-Community,
attached is a patch that probably could be applied upstream:
It is ... Fixing unaligned memory accesses ...
Details to this patch could be read under
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=656955

I rechecked against latest git.
As far as I can see, it's not applied yet.


Best Regards
Holger Fischer

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Author: Shawn Landen <shawnlandden@gmail.com>
Description: Fixing unaligned memory accesses (Closes: #656955).

Index: b/ctree.h
===================================================================
--- a/ctree.h
+++ b/ctree.h
@@ -19,6 +19,8 @@
 #ifndef __BTRFS__
 #define __BTRFS__
 
+#include <stdint.h>
+
 #if BTRFS_FLAT_INCLUDES
 #include "list.h"
 #include "kerncompat.h"
@@ -1072,13 +1074,17 @@ struct btrfs_root {
 static inline u##bits btrfs_##name(struct extent_buffer *eb)		\
 {									\
 	struct btrfs_header *h = (struct btrfs_header *)eb->data;	\
-	return le##bits##_to_cpu(h->member);				\
+	uint##bits##_t t;						\
+	memcpy(&t, &h->member, sizeof(h->member));			\
+	return le##bits##_to_cpu(t);					\
 }									\
 static inline void btrfs_set_##name(struct extent_buffer *eb,		\
 				    u##bits val)			\
 {									\
 	struct btrfs_header *h = (struct btrfs_header *)eb->data;	\
-	h->member = cpu_to_le##bits(val);				\
+	uint##bits##_t t;						\
+	t = cpu_to_le##bits(val);					\
+	memcpy(&h->member, &t, sizeof(h->member));			\
 }
 
 #define BTRFS_SETGET_FUNCS(name, type, member, bits)			\
@@ -1104,11 +1110,15 @@ static inline void btrfs_set_##name(stru
 #define BTRFS_SETGET_STACK_FUNCS(name, type, member, bits)		\
 static inline u##bits btrfs_##name(type *s)				\
 {									\
-	return le##bits##_to_cpu(s->member);				\
+	uint##bits##_t t;						\
+	memcpy(&t, &s->member, sizeof(s->member));			\
+	return le##bits##_to_cpu(t);					\
 }									\
 static inline void btrfs_set_##name(type *s, u##bits val)		\
 {									\
-	s->member = cpu_to_le##bits(val);				\
+	uint##bits##_t t;						\
+	t = cpu_to_le##bits(val);					\
+	memcpy(&s->member, &t, sizeof(s->member));			\
 }
 
 BTRFS_SETGET_FUNCS(device_type, struct btrfs_dev_item, type, 64);
Index: b/volumes.c
===================================================================
--- a/volumes.c
+++ b/volumes.c
@@ -425,10 +425,11 @@ static int find_next_chunk(struct btrfs_
 		if (found_key.objectid != objectid)
 			*offset = 0;
 		else {
+			u64 t;
 			chunk = btrfs_item_ptr(path->nodes[0], path->slots[0],
 					       struct btrfs_chunk);
-			*offset = found_key.offset +
-				btrfs_chunk_length(path->nodes[0], chunk);
+			t = found_key.offset + btrfs_chunk_length(path->nodes[0], chunk);
+			memcpy(offset, &t, sizeof(found_key.offset));
 		}
 	}
 	ret = 0;

Re: btrfs-tools: debian/patches/09-unaligned-memaccess.patch

[David Sterba]

On Wed, May 22, 2013 at 07:08:42AM +0200, Holger Fischer wrote:
> Dear BTRFS-Community,
> attached is a patch that probably could be applied upstream:
> It is ... Fixing unaligned memory accesses ...
> Details to this patch could be read under
> http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=656955
> 
> I rechecked against latest git.
> As far as I can see, it's not applied yet.

I had been applied, but had to be updated further, see

https://git.kernel.org/cgit/linux/kernel/git/mason/btrfs-progs.git/commit/?id=7b668965f0cf3fb8632c505a7a011189ee1a5a8e

"
Replacing memcpy with memmove does't work - gcc treats memmove
the same way it treats memcpy.

This patch brings in {get|put}_unaligned_le{16|32|64} (using the
packed struct method), and uses them in the failing get/set calls.

On architectures where unaligned accesses are cheap, these unaligned
macros should be optimized out by the compiler.
"

What's still missing is get_unaligned_* in the BTRFS_SETGET_STACK_FUNCS
macros.


david