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Subject[PATCH] ubifs: work around high stack usage with clang
Date
Building this file with clang can result in large stack usage as seen from
this warning:

fs/ubifs/auth.c:78:5: error: stack frame size of 1152 bytes in function 'ubifs_prepare_auth_node'

The problem is that inlining ubifs_hash_calc_hmac() leads to
two SHASH_DESC_ON_STACK() blocks in the same function, and clang
for some reason does not reuse the stack space as it should.

Putting the first declaration into a separate basic block avoids
this problem and reduces the stack allocation to 640 bytes.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
fs/ubifs/auth.c | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/fs/ubifs/auth.c b/fs/ubifs/auth.c
index 5bf5fd08879e..5d3d0b37a908 100644
--- a/fs/ubifs/auth.c
+++ b/fs/ubifs/auth.c
@@ -78,7 +78,6 @@ static int ubifs_hash_calc_hmac(const struct ubifs_info *c, const u8 *hash,
int ubifs_prepare_auth_node(struct ubifs_info *c, void *node,
struct shash_desc *inhash)
{
- SHASH_DESC_ON_STACK(hash_desc, c->hash_tfm);
struct ubifs_auth_node *auth = node;
u8 *hash;
int err;
@@ -87,13 +86,17 @@ int ubifs_prepare_auth_node(struct ubifs_info *c, void *node,
if (!hash)
return -ENOMEM;

- hash_desc->tfm = c->hash_tfm;
- hash_desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
- ubifs_shash_copy_state(c, inhash, hash_desc);
+ {
+ SHASH_DESC_ON_STACK(hash_desc, c->hash_tfm);

- err = crypto_shash_final(hash_desc, hash);
- if (err)
- goto out;
+ hash_desc->tfm = c->hash_tfm;
+ hash_desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;
+ ubifs_shash_copy_state(c, inhash, hash_desc);
+
+ err = crypto_shash_final(hash_desc, hash);
+ if (err)
+ goto out;
+ }

err = ubifs_hash_calc_hmac(c, hash, auth->hmac);
if (err)
--
2.20.0
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