netdev - Re: [PATCH] net: ipv4: fix clang -Wformat warning

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Date:   Thu, 7 Jul 2022 10:47:28 -0700
From:   Justin Stitt <justinstitt@...gle.com>
To:     Joe Perches <joe@...ches.com>
Cc:     Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S . Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] net: ipv4: fix clang -Wformat warning

On Thu, Jul 7, 2022 at 10:40 AM Joe Perches <joe@...ches.com> wrote:
>
> On Thu, 2022-07-07 at 10:30 -0700, Justin Stitt wrote:
> > When building with Clang we encounter this warning:
> > > net/ipv4/ah4.c:513:4: 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.
>
> I think it also makes sense to use %u and not %d
> as the original type is unsigned.
Yeah, that would also work. An integer (even a signed one) fully
encompasses a u16 so it's really a choice of style. Do you think the
change to %u warrants a v2 of this patch?
>
> > diff --git a/net/ipv4/ah4.c b/net/ipv4/ah4.c
> []
> > @@ -507,7 +507,7 @@ static int ah_init_state(struct xfrm_state *x)
> >
> >       if (aalg_desc->uinfo.auth.icv_fullbits/8 !=
> >           crypto_ahash_digestsize(ahash)) {
> > -             pr_info("%s: %s digestsize %u != %hu\n",
> > +             pr_info("%s: %s digestsize %u != %d\n",
> >                       __func__, x->aalg->alg_name,
> >                       crypto_ahash_digestsize(ahash),
> >                       aalg_desc->uinfo.auth.icv_fullbits / 8);
>