Date: Tue, 11 Oct 2011 14:52:17 -0400 From: Arnaud Lacombe <lacombar@gmail.com> To: Larry Rosenman <ler@lerctr.org> Cc: =?ISO-8859-1?Q?Ren=E9_Ladan?= <rene@freebsd.org>, freebsd-current@freebsd.org, Dimitry Andric <dim@freebsd.org> Subject: Re: System headers with clang? Message-ID: <CACqU3MVETLMRuYuVpZ0aehdr7rX4KqZGFG17pKdFeSut7jOCCw@mail.gmail.com> In-Reply-To: <4E948D59.5020006@lerctr.org> References: <alpine.BSF.2.00.1110091229550.43656@lrosenman.dyndns.org> <4E942FF1.9000805@FreeBSD.org> <CACqU3MV9vP%2BVUR%2B2Qpzc4mCS1w3R17yvMGNPT%2BxnsGUiYr8VFQ@mail.gmail.com> <4E948D59.5020006@lerctr.org>
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Hi,
On Tue, Oct 11, 2011 at 2:39 PM, Larry Rosenman <ler@lerctr.org> wrote:
> On 10/11/2011 1:36 PM, Arnaud Lacombe wrote:
>>
>> Hi,
>>
>> On Tue, Oct 11, 2011 at 8:00 AM, Dimitry Andric<dim@freebsd.org> =A0wrot=
e:
>>>
>>> On 2011-10-09 19:32, Larry Rosenman wrote:
>>>>
>>>> I had gotten a PR about sysutils/lsof not compiling with clang. =A0I h=
ad
>>>> Vic Abell check it out, and the problem is NOT with lsof per se, but
>>>> with the system headers.
>>>>
>>>> Is there a project afoot to update the system headers to make them cla=
ng
>>>> compilable?
>>>
>>> The problem isn't that clang can't compile the system headers, but
>>> normally these don't get included from userspace. =A0And they certainly
>>> won't work as expected when you define _KERNEL in userspace, as the lso=
f
>>> port foolishly does. =A0It probably can't be avoided in such a tool,
>>> though.
>>>
>> #ifdef _KERNEL/#endif protected part of system headers shall NEVER be
>> accessed by userland. It is a fault to have them present in
>> /usr/include. Linux got it right there, all those part are removed
>> upon headers' installation.
>>
>> =A0- Arnaud
>
> Then lsof would NOT be compilable / usable at all, as it delves into
> /dev/kmem to get information.
>
AFAIK, Linux is capable of supporting lsof in a backward compatible
manner, without exposing its internal guts.
FWIW, KVM is a bad kernel/userland interface, as it does not guarantee
backward compatibility.
> And it **NEEDS** to know what the structures are.
>
No, not kernel-only structure. Now, if these structure are not meant
to be kernel only, move them out of _KERNEL area, but beware of
backward compatibility issue in the future.
> That is unless someone(tm) writes the Kernel interfaces to get the info.
>
Yes, this is the core of the problem and a classical chicken/eggs
problem solves the very wrongest way.
At some point, I thought to modify the build system to pass kernel's
headers through unifdef(1), but I quickly forgot about that:
% git grep 'define _KERNEL' * | grep -v '^sys' | wc -l
27
- Arnaud
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