Re: [PATCH v2] mac80211: LLVMLinux: Remove VLAIS usage from mac80211

On Fri, Mar 07, 2014 at 06:15:43PM -0800, Behan Webster wrote:

On 03/07/14 17:56, Joe Perches wrote:

quoted

On Fri, 2014-03-07 at 17:26 -0800, behanw@converseincode.com wrote:

quoted

From: Jan-Simon Möller <redacted>

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

[]

quoted

diff --git a/net/mac80211/aes_ccm.c b/net/mac80211/aes_ccm.c

[]

quoted

@@ -23,12 +23,14 @@ void ieee80211_aes_ccm_encrypt(struct crypto_aead *tfm, u8 *b_0, u8 *aad,
 			       u8 *data, size_t data_len, u8 *mic)
 {
 	struct scatterlist assoc, pt, ct[2];
-	struct {
-		struct aead_request	req;
-		u8			priv[crypto_aead_reqsize(tfm)];
-	} aead_req;
-	memset(&aead_req, 0, sizeof(aead_req));
+	char aead_req_data[sizeof(struct aead_request) +
+				crypto_aead_reqsize(tfm) +
+				CRYPTO_MINALIGN] CRYPTO_MINALIGN_ATTR;

Can this be a too large amount of stack?

Is crypto_aead_reqsize() limited to < ~1k?

Perhaps it'd be better to use kzalloc for this
or another reserved pool

No more stack being used than with the the original code. The stack
memory use is identical.

Could you explain that? It looks like aead_req_data can be bigger than
original struct aead_req up to CRYPTO_MINALIGN bytes. IOW adding
CRYPTO_MINALIGN to size seems unneeded as aead_request->__ctx alignment
requirement should by assured by proper sizeof(struct aead_request).

Besides, why not add VLAIS feature to llvm instead of fixing all
programs that use it?

Stanislaw