crypto: Replace zero-length array with flexible-array member

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/caam/caamalg.c

@@ -909,7 +909,7 @@ struct skcipher_edesc {
 	bool bklog;
 	dma_addr_t sec4_sg_dma;
 	struct sec4_sg_entry *sec4_sg;
-	u32 hw_desc[0];
+	u32 hw_desc[];
 };
 
 static void caam_unmap(struct device *dev, struct scatterlist *src,

drivers/crypto/caam/caamalg_qi.c

@@ -783,7 +783,7 @@ struct aead_edesc {
 	unsigned int assoclen;
 	dma_addr_t assoclen_dma;
 	struct caam_drv_req drv_req;
-	struct qm_sg_entry sgt[0];
+	struct qm_sg_entry sgt[];
 };
 
 /*
@@ -803,7 +803,7 @@ struct skcipher_edesc {
 	int qm_sg_bytes;
 	dma_addr_t qm_sg_dma;
 	struct caam_drv_req drv_req;
-	struct qm_sg_entry sgt[0];
+	struct qm_sg_entry sgt[];
 };
 
 static struct caam_drv_ctx *get_drv_ctx(struct caam_ctx *ctx,

drivers/crypto/caam/caamalg_qi2.h

@@ -114,7 +114,7 @@ struct aead_edesc {
 	dma_addr_t qm_sg_dma;
 	unsigned int assoclen;
 	dma_addr_t assoclen_dma;
-	struct dpaa2_sg_entry sgt[0];
+	struct dpaa2_sg_entry sgt[];
 };
 
 /*
@@ -132,7 +132,7 @@ struct skcipher_edesc {
 	dma_addr_t iv_dma;
 	int qm_sg_bytes;
 	dma_addr_t qm_sg_dma;
-	struct dpaa2_sg_entry sgt[0];
+	struct dpaa2_sg_entry sgt[];
 };
 
 /*
@@ -146,7 +146,7 @@ struct ahash_edesc {
 	dma_addr_t qm_sg_dma;
 	int src_nents;
 	int qm_sg_bytes;
-	struct dpaa2_sg_entry sgt[0];
+	struct dpaa2_sg_entry sgt[];
 };
 
 /**

drivers/crypto/caam/caamhash.c

@@ -536,7 +536,7 @@ struct ahash_edesc {
 	int sec4_sg_bytes;
 	bool bklog;
 	u32 hw_desc[DESC_JOB_IO_LEN_MAX / sizeof(u32)] ____cacheline_aligned;
-	struct sec4_sg_entry sec4_sg[0];
+	struct sec4_sg_entry sec4_sg[];
 };
 
 static inline void ahash_unmap(struct device *dev,

drivers/crypto/cavium/nitrox/nitrox_main.c

@@ -71,7 +71,7 @@ struct ucode {
 	char version[VERSION_LEN - 1];
 	__be32 code_size;
 	u8 raz[12];
-	u64 code[0];
+	u64 code[];
 };
 
 /**

drivers/crypto/chelsio/chcr_core.h

@@ -68,7 +68,7 @@ struct _key_ctx {
 	__be32 ctx_hdr;
 	u8 salt[MAX_SALT];
 	__be64 iv_to_auth;
-	unsigned char key[0];
+	unsigned char key[];
 };
 
 #define KEYCTX_TX_WR_IV_S  55

drivers/crypto/mediatek/mtk-sha.c

@@ -107,7 +107,7 @@ struct mtk_sha_ctx {
 	u8 id;
 	u8 buf[SHA_BUF_SIZE] __aligned(sizeof(u32));
 
-	struct mtk_sha_hmac_ctx	base[0];
+	struct mtk_sha_hmac_ctx	base[];
 };
 
 struct mtk_sha_drv {

drivers/crypto/nx/nx.h

@@ -37,7 +37,7 @@ struct max_sync_cop {
 	u32 fc;
 	u32 mode;
 	u32 triplets;
-	struct msc_triplet trip[0];
+	struct msc_triplet trip[];
 } __packed;
 
 struct alg_props {

drivers/crypto/omap-sham.c

@@ -159,7 +159,7 @@ struct omap_sham_reqctx {
 	int			sg_len;
 	unsigned int		total;	/* total request */
 
-	u8			buffer[0] OMAP_ALIGNED;
+	u8			buffer[] OMAP_ALIGNED;
 };
 
 struct omap_sham_hmac_ctx {
@@ -176,7 +176,7 @@ struct omap_sham_ctx {
 	/* fallback stuff */
 	struct crypto_shash	*fallback;
 
-	struct omap_sham_hmac_ctx base[0];
+	struct omap_sham_hmac_ctx base[];
 };
 
 #define OMAP_SHAM_QUEUE_LENGTH	10

include/crypto/if_alg.h

@@ -66,7 +66,7 @@ struct af_alg_sgl {
 struct af_alg_tsgl {
 	struct list_head list;
 	unsigned int cur;		/* Last processed SG entry */
-	struct scatterlist sg[0];	/* Array of SGs forming the SGL */
+	struct scatterlist sg[];	/* Array of SGs forming the SGL */
 };
 
 #define MAX_SGL_ENTS ((4096 - sizeof(struct af_alg_tsgl)) / \