[PATCH AUTOSEL 4.19 31/31] gcc-10: avoid shadowing standard library 'free()' in crypto

From: Sasha Levin
Date: Thu May 14 2020 - 15:03:20 EST


From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>

[ Upstream commit 1a263ae60b04de959d9ce9caea4889385eefcc7b ]

gcc-10 has started warning about conflicting types for a few new
built-in functions, particularly 'free()'.

This results in warnings like:

crypto/xts.c:325:13: warning: conflicting types for built-in function âfreeâ; expected âvoid(void *)â [-Wbuiltin-declaration-mismatch]

because the crypto layer had its local freeing functions called
'free()'.

Gcc-10 is in the wrong here, since that function is marked 'static', and
thus there is no chance of confusion with any standard library function
namespace.

But the simplest thing to do is to just use a different name here, and
avoid this gcc mis-feature.

[ Side note: gcc knowing about 'free()' is in itself not the
mis-feature: the semantics of 'free()' are special enough that a
compiler can validly do special things when seeing it.

So the mis-feature here is that gcc thinks that 'free()' is some
restricted name, and you can't shadow it as a local static function.

Making the special 'free()' semantics be a function attribute rather
than tied to the name would be the much better model ]

Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
crypto/lrw.c | 6 +++---
crypto/xts.c | 6 +++---
2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/crypto/lrw.c b/crypto/lrw.c
index 11d079c44cafc..871664158c161 100644
--- a/crypto/lrw.c
+++ b/crypto/lrw.c
@@ -453,7 +453,7 @@ static void exit_tfm(struct crypto_skcipher *tfm)
crypto_free_skcipher(ctx->child);
}

-static void free(struct skcipher_instance *inst)
+static void free_inst(struct skcipher_instance *inst)
{
crypto_drop_skcipher(skcipher_instance_ctx(inst));
kfree(inst);
@@ -565,12 +565,12 @@ static int create(struct crypto_template *tmpl, struct rtattr **tb)
inst->alg.encrypt = encrypt;
inst->alg.decrypt = decrypt;

- inst->free = free;
+ inst->free = free_inst;

err = skcipher_register_instance(tmpl, inst);
if (err) {
err_free_inst:
- free(inst);
+ free_inst(inst);
}
return err;
}
diff --git a/crypto/xts.c b/crypto/xts.c
index a19965a0fe932..6f51052039837 100644
--- a/crypto/xts.c
+++ b/crypto/xts.c
@@ -393,7 +393,7 @@ static void exit_tfm(struct crypto_skcipher *tfm)
crypto_free_cipher(ctx->tweak);
}

-static void free(struct skcipher_instance *inst)
+static void free_inst(struct skcipher_instance *inst)
{
crypto_drop_skcipher(skcipher_instance_ctx(inst));
kfree(inst);
@@ -504,12 +504,12 @@ static int create(struct crypto_template *tmpl, struct rtattr **tb)
inst->alg.encrypt = encrypt;
inst->alg.decrypt = decrypt;

- inst->free = free;
+ inst->free = free_inst;

err = skcipher_register_instance(tmpl, inst);
if (err) {
err_free_inst:
- free(inst);
+ free_inst(inst);
}
return err;
}
--
2.20.1