Date: Tue, 11 Oct 2011 14:04:49 -0500 From: Larry Rosenman <ler@lerctr.org> To: Arnaud Lacombe <lacombar@gmail.com> 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: <4E949351.5040904@lerctr.org> In-Reply-To: <CACqU3MVETLMRuYuVpZ0aehdr7rX4KqZGFG17pKdFeSut7jOCCw@mail.gmail.com> 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> <CACqU3MVETLMRuYuVpZ0aehdr7rX4KqZGFG17pKdFeSut7jOCCw@mail.gmail.com>
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On 10/11/2011 1:52 PM, Arnaud Lacombe wrote: > 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> wrote: >>>> On 2011-10-09 19:32, Larry Rosenman wrote: >>>>> I had gotten a PR about sysutils/lsof not compiling with clang. I had >>>>> 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 clang >>>>> compilable? >>>> The problem isn't that clang can't compile the system headers, but >>>> normally these don't get included from userspace. And they certainly >>>> won't work as expected when you define _KERNEL in userspace, as the lsof >>>> port foolishly does. It 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. >>> >>> - 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. Therein lies the rub. In order to do it's job, it DOES need to grovel around in kernel only structures. > >> 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 This is not going to fix things until/unless someone(tm) takes the bull by the horns, and writes a userland<->kernel interface to get ALL the data that lsof currently gathers from groveling around in /dev/kmem. I don't have the skills nor time to do that. We can go around and around on this topic, but until/unless either the clang headers/built-ins are changed to match the system/kernel headers, or someone(tm) writes the interfaces, clang will NOT be supported to compile sysutils/lsof. -- Larry Rosenman http://www.lerctr.org/~ler Phone: +1 512-248-2683 E-Mail: ler@lerctr.org US Mail: 430 Valona Loop, Round Rock, TX 78681-3893
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