From: Alejandro Colomar <colomar.6.4.3@gmail.com>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Glibc may provide a safe nitems(), and also __must_be_array()
Date: Mon, 28 Sep 2020 11:48:31 +0200 [thread overview]
Message-ID: <71c25cb0-9fa2-4e97-c93c-44eadfd781fb@gmail.com> (raw)
Hi Rusty,
I have a few related questions about the kernel.
I have never written kernel code, so maybe you have some configuration
that I don't know, but I've seen a few things that look a bit weird.
1)
The kernel has ARRAY_SIZE() in <linux/kernel.h>,
but still a lot of files either use the raw sizeof division, or
define a simple ARRAY_SIZE() (sometimes with that name,
and sometimes with a different name) without using __must_be_array()
(and therefore being unsafe).
Is there any reason for any of those files to not use the definition in
<linux/kernel.h>, or should all of them be fixed to use it?
2)
Glibc may provide __must_be_array() in the near future.
I designed it so that it should be 100% compatible with the one in
<linux/compiler.h>. It will be provided in <sys/param.h>.
I'd add a
#if !defined(__must_be_array) [...] #endif
enclosing its definition in <linux/compiler.h>,
to avoid possible redefinitions.
3)
Does the kernel always compile against glibc?
If that's the case, the kernel could include <sys/param.h> to get the
definitions of __must_be_array() and nitems(), couldn't it
(if/when they merge the patch I sent, of course)?
If not, I'd like to know which other libraries are possible, and I'd
like to patch them to also have nitems() and __must_be_array().
4)
I'd like to know your thoughts about the following macro for getting
array sizes in bytes safely:
#define array_bytes(arr) (sizeof(arr) + __must_be_array(arr))
I already have a patch prepared for glibc, in case they merge nitems().
It would help get rid once and for all of a whole class of bugs,
and at the same time allow for the sintactic sugar of
arrays in function parameters:
https://lkml.org/lkml/2015/9/3/428
I'll be happy to write any patches for the kernel that are neccessary
related to these things.
Thanks,
Alex
reply other threads:[~2020-09-28 9:48 UTC|newest]
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