Re: Unused macro

["Alejandro Colomar (man-pages)" <alx.manpages@gmail.com>]

Hi Pablo,

On 4/5/21 11:44 PM, Pablo Neira Ayuso wrote:
>>
>> Then we still have the issue that ARRAY_SIZE is not defined in that
>> header (see a simple test below).  You should probably include some
>> header that provides it.
> 
> SCTP_CHUNKMAP_IS_* macros are used from iptables/extensions/xt_sctp.h
> (iptables userspace codebase). These macros are also used internally
> from net/netfilter/xt_sctp.c. It's using a rather unorthodox trick to
> share code between the kernel and userspace, otherwise iptables would
> need to keep a copy of this code.
> 
> BTW, why do you need xt_sctp.h for the manpages? This header is rather
> specific to the match on sctp from the xtables infrastructure, so it's
> not so useful from a programmer perspective (manpages) I think.

I don't need it.  Actually, I was fixing the includes in the SYNOPSIS, 
and when I was grepping for some variable (I don't even remember which 
one), the search brought me at some point to this header, where the use 
of ARRAY_SIZE() caught my attention :-)

> 
>> But again, if no one noticed this in more than a decade, either no one
>> used this macro, or they included other headers in the same file where
>> they used the macro.  So I'd still rethink if maybe that macro (and
>> possibly others) is really needed.
>>
>> Test 1:
>>
>> [[
>> $ cat test.c
>> #include <linux/netfilter/xt_sctp.h>
>>
>> int foo(int x)
>> {
>> 	int a[x];
>>
>> 	return ARRAY_SIZE(a);
>> }
>> $ cc -Wall -Wextra -Werror test.c -S -o test.s
>> test.c: In function ‘foo’:
>> test.c:7:9: error: implicit declaration of function ‘ARRAY_SIZE’
>> [-Werror=implicit-function-declaration]
>>      7 |  return ARRAY_SIZE(a);
>>        |         ^~~~~~~~~~
>> cc1: all warnings being treated as errors
>> $
>> ]]
> 
> I see, this is breaking self-compilation of the headers.
> 
> If there a need to remove xt_sctp.h from the ignore-list of the header
> self-compilation infrastructure, it should be possible to fix
> userspace to keep its own copy and probably add a #warn on the UAPI
> header to let other possible consumers of this macro that this macro
> will go away at some point.
> 

Well, I ignore what is this header for; I was just reporting something 
that I casually found and might be a bug.  I'll leave the fix to you ;)

Cheers,

Alex

-- 
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/