* [PATCH] ubifs: work around high stack usage with clang
@ 2019-03-24 19:44 ` Arnd Bergmann
0 siblings, 0 replies; 4+ messages in thread
From: Arnd Bergmann @ 2019-03-24 19:44 UTC (permalink / raw)
To: Richard Weinberger, Artem Bityutskiy, Adrian Hunter
Cc: clang-built-linux, Nick Desaulniers, Nathan Chancellor,
Arnd Bergmann, Eric Biggers, Herbert Xu, Sascha Hauer, linux-mtd,
linux-kernel
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
^ permalink raw reply related [flat|nested] 4+ messages in thread
* [PATCH] ubifs: work around high stack usage with clang
@ 2019-03-24 19:44 ` Arnd Bergmann
0 siblings, 0 replies; 4+ messages in thread
From: Arnd Bergmann @ 2019-03-24 19:44 UTC (permalink / raw)
To: Richard Weinberger, Artem Bityutskiy, Adrian Hunter
Cc: Herbert Xu, Arnd Bergmann, Eric Biggers, Sascha Hauer,
Nick Desaulniers, linux-kernel, clang-built-linux, linux-mtd,
Nathan Chancellor
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
______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] ubifs: work around high stack usage with clang
2019-03-24 19:44 ` Arnd Bergmann
@ 2019-03-25 17:57 ` Nick Desaulniers
-1 siblings, 0 replies; 4+ messages in thread
From: Nick Desaulniers @ 2019-03-25 17:57 UTC (permalink / raw)
To: Arnd Bergmann
Cc: Richard Weinberger, Artem Bityutskiy, Adrian Hunter,
clang-built-linux, Nathan Chancellor, Eric Biggers, Herbert Xu,
Sascha Hauer, linux-mtd, LKML
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
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] ubifs: work around high stack usage with clang
@ 2019-03-25 17:57 ` Nick Desaulniers
0 siblings, 0 replies; 4+ messages in thread
From: Nick Desaulniers @ 2019-03-25 17:57 UTC (permalink / raw)
To: Arnd Bergmann
Cc: Herbert Xu, Eric Biggers, Richard Weinberger, Sascha Hauer,
Artem Bityutskiy, Adrian Hunter, LKML, clang-built-linux,
linux-mtd, Nathan Chancellor
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
______________________________________________________
Linux MTD discussion mailing list
http://lists.infradead.org/mailman/listinfo/linux-mtd/
^ permalink raw reply [flat|nested] 4+ messages in thread
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2019-03-24 19:44 [PATCH] ubifs: work around high stack usage with clang Arnd Bergmann
2019-03-24 19:44 ` Arnd Bergmann
2019-03-25 17:57 ` Nick Desaulniers
2019-03-25 17:57 ` Nick Desaulniers
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