netdev - Re: [PATCH iproute2 v2] json_print: Fix hidden 64-bit type promotion

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Message-ID: <20180425075527.680f34fc@xeon-e3>
Date:   Wed, 25 Apr 2018 07:55:27 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Toke Høiland-Jørgensen <toke@...e.dk>
Cc:     netdev@...r.kernel.org,
        Kevin Darbyshire-Bryant <ldir@...byshire-bryant.me.uk>
Subject: Re: [PATCH iproute2 v2] json_print: Fix hidden 64-bit type
 promotion

On Wed, 25 Apr 2018 16:30:22 +0200
Toke Høiland-Jørgensen <toke@...e.dk> wrote:

> print_uint() will silently promote its variable type to uint64_t, but there
> is nothing that ensures that the format string specifier passed along with
> it fits (and the function name suggest to pass "%u").
> 
> Fix this by changing print_uint() to use a native 'unsigned int' type, and
> introduce a separate print_u64() function for printing 64-bit values. All
> call sites that were actually printing 64-bit values using print_uint() are
> converted to use print_u64() instead.
> 
> Since print_int() was already using native int types, just add a
> print_s64() to match, but don't convert any call sites.
> 
> Cc: Kevin Darbyshire-Bryant <ldir@...byshire-bryant.me.uk>
> Signed-off-by: Toke Høiland-Jørgensen <toke@...e.dk>

Yes, this makes sense. Maybe there should be a print_luint for consistency.
Also, I tried (in vain) to make a version that allows GCC to check the
format string.  But it was a struggle and just gave up.