linux-kernel - Re: [PATCH] netfilter: conntrack: fix -Wformat

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Date:   Sun, 8 Nov 2020 08:34:30 +0100 (CET)
From:   Lukas Bulwahn <lukas.bulwahn@...il.com>
To:     Joe Perches <joe@...ches.com>,
        Aditya Srivastava <yashsri421@...il.com>,
        Dwaipayan Ray <dwaipayanray1@...il.com>
cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jozsef Kadlecsik <kadlec@...filter.org>,
        Florian Westphal <fw@...len.de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] netfilter: conntrack: fix -Wformat



On Sat, 7 Nov 2020, Joe Perches wrote:

> On Fri, 2020-11-06 at 23:55 -0800, Nick Desaulniers wrote:
> > Clang is more aggressive about -Wformat warnings when the format flag
> > specifies a type smaller than the parameter. Fixes 8 instances of:
> > 
> > warning: format specifies type 'unsigned short' but the argument has
> > type 'int' [-Wformat]
> 
> Likely clang's -Wformat message is still bogus.
> Wasn't that going to be fixed?
> 
> Integer promotions are already done on these types to int anyway.
> Didn't we have this discussion last year?
> 
> https://lore.kernel.org/lkml/CAKwvOd=mqzj2pAZEUsW-M_62xn4pijpCJmP=B1h_-wEb0NeZsA@mail.gmail.com/
> https://lore.kernel.org/lkml/CAHk-=wgoxnmsj8GEVFJSvTwdnWm8wVJthefNk2n6+4TC=20e0Q@mail.gmail.com/
> https://lore.kernel.org/lkml/a68114afb134b8633905f5a25ae7c4e6799ce8f1.camel@perches.com/
> 
> Look at commit cbacb5ab0aa0 ("docs: printk-formats: Stop encouraging use
> of unnecessary %h[xudi] and %hh[xudi]")
> 
> The "h" and "hh" things should never be used. The only reason for them
> being used if if you have an "int", but you want to print it out as a
> "char" (and honestly, that is a really bad reason, you'd be better off
> just using a proper cast to make the code more obvious).
>

Joe, would this be a good rule to check for in checkpatch?

Can Dwaipayan or Aditya give it a try to create a suitable patch to add 
such a rule?

Dwaipayan, Aditya, if Joe thinks it is worth a rule, it is "first come, 
first serve" for you to take that task. 

Lukas

> So if what you have a "char" (or unsigned char) you should always just
> print it out as an "int", knowing that the compiler already did the
> proper type conversion.
> 
> > diff --git a/net/netfilter/nf_conntrack_standalone.c b/net/netfilter/nf_conntrack_standalone.c
> []
> > @@ -50,38 +50,38 @@ print_tuple(struct seq_file *s, const struct nf_conntrack_tuple *tuple,
> >  
> > 
> >  	switch (l4proto->l4proto) {
> >  	case IPPROTO_ICMP:
> > -		seq_printf(s, "type=%u code=%u id=%u ",
> > +		seq_printf(s, "type=%u code=%u id=%hu ",
> 
> etc...
> 
> 
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