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Date:   Thu,  7 Jul 2022 11:15:32 -0700
Message-Id: <20220707181532.762452-1-justinstitt@google.com>
Mime-Version: 1.0
Subject: [PATCH] net: ipv4: esp4: fix clang -Wformat warning
From:   Justin Stitt <justinstitt@google.com>
To:     Steffen Klassert <steffen.klassert@secunet.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S . Miller" <davem@davemloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        David Ahern <dsahern@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>
Cc:     Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
        Justin Stitt <justinstitt@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

When building with Clang we encounter this warning:
| net/ipv4/esp4.c:1114:5: error: format specifies type 'unsigned short'
| but the argument has type 'int' [-Werror,-Wformat]
| aalg_desc->uinfo.auth.icv_fullbits / 8);

`aalg_desc->uinfo.auth.icv_fullbits` is a u16 but due to default
argument promotion becomes an int.

Variadic functions (printf-like) undergo default argument promotion.
Documentation/core-api/printk-formats.rst specifically recommends using
the promoted-to-type's format flag.

As per C11 6.3.1.1:
(https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1548.pdf) `If an int
can represent all values of the original type ..., the value is
converted to an int; otherwise, it is converted to an unsigned int.
These are called the integer promotions.` Thus it makes sense to change
%hu to %d not only to follow this standard but to suppress the warning
as well.

Nathan also mentions: This solution is in line with printk-formats.rst
after commit cbacb5ab0aa0 ("docs: printk-formats: Stop encouraging use
of unnecessary %h[xudi] and %hh[xudi]").

Link: https://github.com/ClangBuiltLinux/linux/issues/378
Suggested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
This is the exact same issue (and fix) as:
https://lore.kernel.org/all/20220707173040.704116-1-justinstitt@google.com/

This really should have been a 2-patch series but I've been going
through warnings and systematically fixing them whilst submitting
patches as I go.

 net/ipv4/esp4.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
index b21238df3301..de48dcac18eb 100644
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -1108,7 +1108,7 @@ static int esp_init_authenc(struct xfrm_state *x)
 		err = -EINVAL;
 		if (aalg_desc->uinfo.auth.icv_fullbits / 8 !=
 		    crypto_aead_authsize(aead)) {
-			pr_info("ESP: %s digestsize %u != %hu\n",
+			pr_info("ESP: %s digestsize %u != %d\n",
 				x->aalg->alg_name,
 				crypto_aead_authsize(aead),
 				aalg_desc->uinfo.auth.icv_fullbits / 8);
-- 
2.37.0.rc0.161.g10f37bed90-goog