linux-kernel - Re: [PATCH] docs: add extra integer types to printk-formats

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Date:   Tue, 5 Mar 2019 12:07:25 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Joe Perches <joe@...ches.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Louis Taylor <louis@...gniz.eu>,
        Jonathan Corbet <corbet@....net>, pmladek@...e.com,
        geert+renesas@...der.be, linux-doc@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux@...glegroups.com,
        Jon Flatley <jflat@...omium.org>
Subject: Re: [PATCH] docs: add extra integer types to printk-formats

On Tue, Mar 05, 2019 at 11:59:30AM -0800, Joe Perches wrote:
> Many of the -Wformat warnings are bogus too.
> 
> There's nothing wrong with using %x for a unsigned int
> of less than long size. (u8/u16)

I believe you to be incorrect.

6.5.2.2 Function calls

7 If the expression that denotes the called function has a type that does
  include a prototype, the arguments are implicitly converted, as if by
  assignment, to the types of the corresponding parameters, taking the
  type of each parameter to be the unqualified version of its declared
  type. The ellipsis notation in a function prototype declarator causes
  argument type conversion to stop after the last declared parameter. The
  default argument promotions are performed on trailing arguments.

I could define a calling convention for my CPU which says to pack u8s
and u16s as tightly as possible in registers (or on the stack), rather
than the prevailing calling convention of having each argument take up
at least one register-sized slot.