linux-kernel - Re: [PATCH v2 1/2] system_data

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Date:   Fri, 2 Oct 2020 10:00:21 -0700
From:   Paul Eggert <eggert@...ucla.edu>
To:     David Laight <David.Laight@...LAB.COM>,
        'Alejandro Colomar' <colomar.6.4.3@...il.com>
Cc:     "mtk.manpages@...il.com" <mtk.manpages@...il.com>,
        "linux-man@...r.kernel.org" <linux-man@...r.kernel.org>,
        "libc-alpha@...rceware.org" <libc-alpha@...rceware.org>,
        "gcc@....gnu.org" <gcc@....gnu.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] system_data_types.7: Add 'void *'

On 10/2/20 2:10 AM, David Laight wrote:
>>   > Also, you should
>>   > warn that because one can convert from any pointer type to void * and
>>   > then to any other pointer type, it's a deliberate hole in C's
>>   > type-checking.
>>
> That isn't what the C standard says at all.
> What is says is that you can cast any data pointer to 'void *'
> and then cast it back to the same type.

I was talking about compile-time checking; you're talking about run-time 
behavior. We're both right in our own domains. It is a tricky area, and this 
suggests that perhaps we shouldn't be trying to document this stuff in a 
libc/kernel manual.