Re: Fail to build s6 on GNU/Hurd

From: Laurent Bercot <>
Date: Sat, 21 Mar 2020 13:40:43 +0000

>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
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

  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

  The fix is in the latest skalibs git. It's too small a bug to cut a
release just from that, so please grab the patch from git.

  If there was a Hurd machine somewhere I could get an account on, I
could spot that kind of build failures before releasing. Hint, hint. ;)

Received on Sat Mar 21 2020 - 13:40:43 UTC

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