[RFC,6/6] btrfs: LLVMLinux: Remove VLAIS

Commit Message

Behan Webster Sept. 2, 2014, 10:32 p.m. UTC

From: Vinícius Tinti <[e-mail]>

Replaced the use of a Variable Length Array In Struct (VLAIS) with a C99
compliant equivalent. This is the original VLAIS struct.

struct {
	struct shash_desc shash;
	char ctx[crypto_shash_descsize(tfm)];
} desc;

This patch instead allocates the appropriate amount of memory using an char
array.

The new code can be compiled with both gcc and clang.

struct shash_desc contains a flexible array member member ctx declared with
CRYPTO_MINALIGN_ATTR, so sizeof(struct shash_desc) aligns the beginning
of the array declared after struct shash_desc with long long.

No trailing padding is required because it is not a struct type that can
be used in an array.

The CRYPTO_MINALIGN_ATTR is required so that desc is aligned with long long
as would be the case for a struct containing a member with
CRYPTO_MINALIGN_ATTR.

Signed-off-by: Jan-Simon Möller <[e-mail]>
Signed-off-by: Behan Webster <[e-mail]>
Signed-off-by: Vinícius Tinti <[e-mail]>
Signed-off-by: Mark Charlebois <[e-mail]>
---
 fs/btrfs/hash.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

Patch

diff --git a/fs/btrfs/hash.c b/fs/btrfs/hash.c
index 85889aa..2fdacda 100644
--- a/fs/btrfs/hash.c
+++ b/fs/btrfs/hash.c
@@ -33,18 +33,18 @@  void btrfs_hash_exit(void)
 
 u32 btrfs_crc32c(u32 crc, const void *address, unsigned int length)
 {
-	struct {
-		struct shash_desc shash;
-		char ctx[crypto_shash_descsize(tfm)];
-	} desc;
+	char desc[sizeof(struct shash_desc)
+		+ crypto_shash_descsize(tfm)] CRYPTO_MINALIGN_ATTR;
+	struct shash_desc *shash = (struct shash_desc *)desc;
+	u32 *ctx = (u32 *)shash_desc_ctx(shash);
 	int err;
 
-	desc.shash.tfm = tfm;
-	desc.shash.flags = 0;
-	*(u32 *)desc.ctx = crc;
+	shash->tfm = tfm;
+	shash->flags = 0;
+	*ctx = crc;
 
-	err = crypto_shash_update(&desc.shash, address, length);
+	err = crypto_shash_update(shash, address, length);
 	BUG_ON(err);
 
-	return *(u32 *)desc.ctx;
+	return *ctx;
 }