jbd2: Avoid dozens of -Wflex-array-member-not-at-end warnings

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are getting ready to enable it, globally.

Use the DEFINE_RAW_FLEX() helper for an on-stack definition of a flexible structure (struct shash_desc) where the size of the flexible-array member (__ctx) is known at compile-time, and refactor the rest of the code, accordingly.

So, with this, fix 77 of the following warnings:

include/linux/jbd2.h:1800:35: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Signed-off-by Gustavo A. R. Silva <[email protected]>

---
Changes in v2:
- Use DIV_ROUND_UP() to compute the number of elements for the flex array. (Jan Kara)

v1:
- Link: https://lore.kernel.org/linux-hardening/ZxvyavDjXDaV9cNg@kspp/

 include/linux/jbd2.h | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

include/linux/jbd2.h +7 -8

index 8aef9bb6ad57..50f7ea8714bf 100644
@@ -1796,22 +1796,21 @@ static inline unsigned long jbd2_log_space_left(journal_t *journal)
 static inline u32 jbd2_chksum(journal_t *journal, u32 crc,
 			      const void *address, unsigned int length)
 {
-	struct {
-		struct shash_desc shash;
-		char ctx[JBD_MAX_CHECKSUM_SIZE];
-	} desc;
+	DEFINE_RAW_FLEX(struct shash_desc, desc, __ctx,
+		DIV_ROUND_UP(JBD_MAX_CHECKSUM_SIZE,
+			     sizeof(*((struct shash_desc *)0)->__ctx)));
 	int err;
 
 	BUG_ON(crypto_shash_descsize(journal->j_chksum_driver) >
 		JBD_MAX_CHECKSUM_SIZE);
 
-	desc.shash.tfm = journal->j_chksum_driver;
-	*(u32 *)desc.ctx = crc;
+	desc->tfm = journal->j_chksum_driver;
+	*(u32 *)desc->__ctx = crc;
 
-	err = crypto_shash_update(&desc.shash, address, length);
+	err = crypto_shash_update(desc, address, length);
 	BUG_ON(err);
 
-	return *(u32 *)desc.ctx;
+	return *(u32 *)desc->__ctx;
 }
 
 /* Return most recent uncommitted transaction */

Signature · 1 line

2.43.0

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are getting ready to enable it, globally.

Use the DEFINE_RAW_FLEX() helper for an on-stack definition of a flexible structure (struct shash_desc) where the size of the flexible-array member (__ctx) is known at compile-time, and refactor the rest of the code, accordingly.

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