| Message ID | 20190324194505.3244479-1-arnd@arndb.de |
|---|---|
| State | Accepted |
| Commit | f4844b35d68ab49c41d542c501fffb46ad81009a |
| Headers | show |
| Series | ubifs: work around high stack usage with clang | expand |
On Sun, Mar 24, 2019 at 12:45 PM Arnd Bergmann <arnd@arndb.de> wrote: > > 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> LGTM; in general, it can be useful to always include a comment before a new scope like: /* New scope to limit lifetime of large stack allocated hash_desc. */ but folks can always refer to the git blame/log for reasoning as to why a new scope was added. I plan on working on a pass in LLVM to improve stack slot reuse sometime in 2019Q2. Thanks for this patch. Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> > --- > 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 > -- Thanks, ~Nick Desaulniers
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)
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(-) -- 2.20.0