linux-kernel - Re: [PATCH for-next 13/25] compiler_types.h: Remove __compiletime_object

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Date:   Mon, 23 Aug 2021 08:43:15 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Daniel Micay <danielmicay@...il.com>,
        Francis Laniel <laniel_francis@...vacyrequired.com>,
        Bart Van Assche <bvanassche@....org>,
        David Gow <davidgow@...gle.com>, linux-mm@...ck.org,
        clang-built-linux@...glegroups.com, linux-hardening@...r.kernel.org
Subject: Re: [PATCH for-next 13/25] compiler_types.h: Remove
 __compiletime_object_size()

On 22/08/2021 09.51, Kees Cook wrote:

> -	int sz = __compiletime_object_size(addr);
> +	int sz = __builtin_object_size(addr, 0);

Not directly related to this patch, but seeing this I wonder if there
would be some value in introducing names for those magic 0/1/2/3 that
are used with __b_o_s. Every time I stumble on code using that I have to
go to the gcc docs, and even then it takes me a while to grok what

     TYPE is an integer constant from 0 to 3.  If the least significant
     bit is clear, objects are whole variables, if it is set, a closest
     surrounding subobject is considered the object a pointer points to.
     The second bit determines if maximum or minimum of remaining bytes
     is computed.

means. The names don't need to be too verbose, just having a few
#defines in-tree with the above quoted above them makes it a lot easier
to figure out what they mean.

Rasmus