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[2/4] hash: use alloca instead of vla trivial

Message ID 1712250913-1977-3-git-send-email-roretzla@linux.microsoft.com (mailing list archive)
State Superseded
Headers
Series RFC samples converting VLA to alloca |

Checks

Context Check Description
ci/checkpatch success coding style OK

Commit Message

Tyler Retzlaff April 4, 2024, 5:15 p.m. UTC 
  RFC sample illustrating simple conversion of VLA to alloca() where
dimension multiplier removed.

Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
---
 lib/hash/rte_thash.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Morten Brørup April 6, 2024, 4:01 p.m. UTC | #1 
> From: Tyler Retzlaff [mailto:roretzla@linux.microsoft.com]
> Sent: Thursday, 4 April 2024 19.15
> 
> RFC sample illustrating simple conversion of VLA to alloca() where
> dimension multiplier removed.
> 
> Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> ---

[...]

>  {
> -	uint32_t tmp_tuple[tuple_len / sizeof(uint32_t)];
> +	uint32_t *tmp_tuple = alloca(tuple_len);

This code is in the rte_thash_adjust_tuple() function [1].

I think we could use a constant size array here, making it large enough for what we think would suffice for any realistic purpose.

The function could check the tuple_len parameter at runtime and return an error value if too big for the array.
It could also check the tuple_len parameter, if constant, at build time.

[1]: https://elixir.bootlin.com/dpdk/v24.03/source/lib/hash/rte_thash.c#L768
diff mbox series

Patch

diff --git a/lib/hash/rte_thash.c b/lib/hash/rte_thash.c
index 68f653f..633e211 100644
--- a/lib/hash/rte_thash.c
+++ b/lib/hash/rte_thash.c
@@ -771,7 +771,7 @@  struct rte_thash_subtuple_helper *
 	uint32_t desired_value,	unsigned int attempts,
 	rte_thash_check_tuple_t fn, void *userdata)
 {
-	uint32_t tmp_tuple[tuple_len / sizeof(uint32_t)];
+	uint32_t *tmp_tuple = alloca(tuple_len);
 	unsigned int i, j, ret = 0;
 	uint32_t hash, adj_bits;
 	const uint8_t *hash_key;