[PATCH v2] btrfs: LLVMLinux: Remove VLAIS

[PATCH v2] btrfs: LLVMLinux: Remove VLAIS

[behanw]

From: Vinícius Tinti <viniciustinti@gmail.com>

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 <dl9pf@gmx.de>
Signed-off-by: Behan Webster <behanw@converseincode.com>
Signed-off-by: Vinícius Tinti <viniciustinti@gmail.com>
Signed-off-by: Mark Charlebois <charlebm@gmail.com>
---
 fs/btrfs/hash.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/fs/btrfs/hash.c b/fs/btrfs/hash.c
index 85889aa..a62743f 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;
 }
-- 
1.9.1

Re: [PATCH v2] btrfs: LLVMLinux: Remove VLAIS

[Chris Mason]

On 09/05/2014 06:58 PM, behanw@converseincode.com wrote:
> From: Vinícius Tinti <viniciustinti@gmail.com>
> 
> 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.

We copied this from one of the other crypto api users, and I'm sure
cooking up all these patches was not a great way to your afternoon.

But, can I talk you into making a helper macro of some kind for this and
putting it into the crypto api headers?  Honestly this setup seems
really error prone.

-chris

> 
> Signed-off-by: Jan-Simon Möller <dl9pf@gmx.de>
> Signed-off-by: Behan Webster <behanw@converseincode.com>
> Signed-off-by: Vinícius Tinti <viniciustinti@gmail.com>
> Signed-off-by: Mark Charlebois <charlebm@gmail.com>
> ---
>  fs/btrfs/hash.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/btrfs/hash.c b/fs/btrfs/hash.c
> index 85889aa..a62743f 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;
>  }
> 

Re: [PATCH v2] btrfs: LLVMLinux: Remove VLAIS

[Behan Webster]

On 09/11/14 09:34, Chris Mason wrote:
>
> On 09/05/2014 06:58 PM, behanw@converseincode.com wrote:
>> From: Vinícius Tinti <viniciustinti@gmail.com>
>>
>> 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.
> We copied this from one of the other crypto api users, and I'm sure
> cooking up all these patches was not a great way to your afternoon.
>
> But, can I talk you into making a helper macro of some kind for this and
> putting it into the crypto api headers?  Honestly this setup seems
> really error prone.
You're not the only person to ask for this. I've got one already coded 
up based on suggestions from tglx.

I've regenerated all the patches. I will resubmit soon.

Will fix.

Behan

-- 
Behan Webster
behanw@converseincode.com