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Re: Bootstrapping glibc vs. dependency on system headers

From: Joseph S. Myers
Subject: Re: Bootstrapping glibc vs. dependency on system headers
Date: Thu, 17 Jan 2013 17:18:41 +0000

On Thu, 17 Jan 2013, Thomas Schwinge wrote:

> Issue 2: Though it will of course never be completely fail-safe,
> candidate header files I identified to remedy this issue and to be used
> in _AC_PROG_PREPROC_WORKS_IFELSE instead of limits.h are: float.h,
> stdarg.h, stddef.h (though the latter might include additional files in
> *BSD environments, which may be supported by glibc, so let's better not
> use that one).  Is using one of float.h and stdarg.h correct in this
> situation, and do you want me to write an Autoconf patch to change that?
> By manually modifying configure, I tested using stdarg.h, and that looks
> fine.

limits.h is unsafe for such bootstrapping, as you found, because of how 
the GCC and glibc copies install each other.

Really, for glibc bootstrapping I don't think you want to include any 
headers there.  If $CPP is defined and nonempty, use that, otherwise use 
$CC -E; no testing for a "working" preprocessor is needed; we require GCC 
4.3 or later for building glibc.

> Issue 3: Assuming fixing Autoconf is the way to go, what do we do in
> glibc until we upgrade to the respective future version of Autoconf?
> Supply our own copy of _AC_PROG_PREPROC_WORKS_IFELSE (or AC_PROG_CPP)?

Yes.  There's already code in configure.in to do something special with 

Joseph S. Myers

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