linux-kernel - [PATCH 5.6 133/194] gcc-10: avoid shadowing standard library free() in crypto

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Date:   Mon, 18 May 2020 19:37:03 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.6 133/194] gcc-10: avoid shadowing standard library free() in crypto

From: Linus Torvalds <torvalds@...ux-foundation.org>

commit 1a263ae60b04de959d9ce9caea4889385eefcc7b upstream.

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 ‘free’; expected ‘void(void *)’ [-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@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 crypto/lrw.c |    4 ++--
 crypto/xts.c |    4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

--- a/crypto/lrw.c
+++ b/crypto/lrw.c
@@ -287,7 +287,7 @@ static void exit_tfm(struct crypto_skcip
 	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);
@@ -400,7 +400,7 @@ static int create(struct crypto_template
 	inst->alg.encrypt = encrypt;
 	inst->alg.decrypt = decrypt;
 
-	inst->free = free;
+	inst->free = free_inst;
 
 	err = skcipher_register_instance(tmpl, inst);
 	if (err)
--- a/crypto/xts.c
+++ b/crypto/xts.c
@@ -322,7 +322,7 @@ static void exit_tfm(struct crypto_skcip
 	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);
@@ -434,7 +434,7 @@ static int create(struct crypto_template
 	inst->alg.encrypt = encrypt;
 	inst->alg.decrypt = decrypt;
 
-	inst->free = free;
+	inst->free = free_inst;
 
 	err = skcipher_register_instance(tmpl, inst);
 	if (err)