Re: Fail to build s6 on GNU/Hurd

From: Shengjing Zhu <>
Date: Sat, 21 Mar 2020 21:47:25 +0800


On Sat, Mar 21, 2020 at 9:40 PM Laurent Bercot <> wrote:
> >For s6 latest release, I fail to build it on GNU/Hurd.
> Hi Shengjing,
> Thanks for the report!
> It's a bug indeed - and a pretty tricky one. In order to work around
> POSIX violations by some systems, skalibs provides certain headers that
> need to be included *before* system headers, and other headers that
> need to be included *after* system headers. That goes against the
> principle of header independence and orthogonality, but unfortunately
> there's no other way to catch stuff like, for instance, EPROTO
> definition missing. (Which, despite their efforts towards compliance
> in the past few years, is still a thing in 2020 in the BSDs.)
> skalibs also tries to provide self-contained headers, i.e. which
> include everything they need. In particular, skalibs/bytestr.h uses
> strnlen in one of its macros, so it needs to make sure to include the
> header that defines strnlen. (So the user can just
> #include <skalibs/bytestr.h> and not worry about anything breaking when
> they use something declared by bytestr.h.)
> The problem is that strnlen, despite being defined by POSIX, is *not*
> declared by every system out there. Almost, but not quite - I don't
> remember whether it's Solaris or MacOS or something that fails to
> declare
> it. So, skalibs declares strnlen in the skalibs/posixishard.h header,
> which is the posix-violation-correction header that needs to be included
> *after* system headers. And to be self-contained, bytestr.h included
> posixishard.h.
> But as shown by your report, it was a mistake. Here several rules are
> conflicting, and bytestr.h did not resolve the conflict properly: as
> your report shows, bytestr.h can be included *before* all necessary
> system headers, like errno.h, are included - so posixishard.h misses
> the EPROTO definition and incorrectly triggers the workaround (which is
> to define it as EPROTOTYPE), and a subsequent inclusion of errno.h
> exposes the problem.
> The correct way to handle this is to explicitly *avoid* including
> exceptional headers such as skalibs/nonposix.h and skalibs/posixishard.h
> in other headers; they should only be used in .c files where header
> inclusion is controlled. The fix is to remove the
> #include <skalibs/posixishard.h>
> line from bytestr.h in skalibs. And if someone uses the str_nlen macro,
> it is their responsibility to also #include <skalibs/posixishard.h> in
> their source file to get the strnlen definition even on non-compliant
> systems.

Thanks for this detail explanation!

Shengjing Zhu
Received on Sat Mar 21 2020 - 13:47:25 UTC

This archive was generated by hypermail 2.3.0 : Sun May 09 2021 - 19:38:49 UTC