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Re: AC_EGREP_CPP and AC_EGREP_HEADER users - beware of recent gcc

From: Eric Blake
Subject: Re: AC_EGREP_CPP and AC_EGREP_HEADER users - beware of recent gcc
Date: Wed, 15 Feb 2017 08:31:11 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0

On 02/15/2017 04:52 AM, Bruno Haible wrote:
> Hi all,
> Some uses of AC_EGREP_CPP and AC_EGREP_HEADER probably assume that when
> no continuation lines (backslash-newline) and no multiline macro invocations
> are involved, each source line produces at most one output line.
> This is no longer the case with GCC >= 5.

> As you can see, here 1 source line produces up to 4 output lines (ignoring the
> line number comment lines). Attempts to use 'grep Version' to find the values 
> of
> __GLIBC__ and __GLIBC_VERSION__ don't work any more.
> Maybe the documentation of AC_EGREP_CPP and AC_EGREP_HEADER could include
> a caveat about this?

Indeed. grep'ping has always been fragile, but adding another warning
can't hurt.  I'll see if I can come up with a patch

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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