[gnutls-dev] Re: pkg-config support for opencdk

Andreas Metzler ametzler at downhill.at.eu.org
Sat Sep 30 18:39:31 CEST 2006

On 2006-08-18 Simon Josefsson <jas at extundo.com> wrote:
> Martin Lambers <marlam at marlam.de> writes:
>> On Tue, 08. Aug 2006, 14:47:39 +0200, Simon Josefsson wrote:
>>> I think Bruno's AC_LIB_HAVE_LINKFLAGS is the best choice.  It works
>>> for cross-compilations, can check for particular versions through the
>>> gnutls.h LIBGNUTLS_VERSION* symbols, and doesn't add unnecessary
>>> libraries to the link line, and works with and without libtool.

>> How does the check for particular versions work with
>> AC_LIB_HAVE_LINKFLAGS? Can you give an example?
> You could modify it into:

>     [#include <gnutls/gnutls.h>
>      #if LIBGNUTLS_VERSION_NUMBER < 0x010500
>      error too old gnutls
>      #endif],
>     [gnutls_certificate_verify_peers2 (0, 0);])

> I didn't test this, but something like it should work.

> Note that the test for gnutls_certificate_verify_peers2() is an
> implicit version test -- gsasl need a gnutls version that have that
> particular feature.  That is the best approach: test the GnuTLS
> library for the properties (e.g., APIs) that your application actually
> needs.  Doing so will work even if someone has back-ported a feature
> to an older version, for example.

I have wasted a bit of time with this today by taking a look at an
obvious candidate, gnutls itself. It currently uses AM_PATH_LIBTASN1
to search for a minimal version of tasn1. Afaiui the version
requirement is not due to some special function only available in this
version but to ignore known to be buggy versions. Libtasn1 doesn't
ship a LIBTASN1_VERSION_NUMBER available for the trick noted above.

I have thought about ways to work around it:

#1 Use a custom autoconf macro to pull the *value* of LIBTASN1_VERSION
from libtasn1.h using the C preprocessor and then compare this string
and GNUTLS_LIBTASN1_VERSION using to be written shell code.
(hideous, imho)

#2 Use asn1_check_version("$GNUTLS_LIBTASN1_VERSION") in
AC_RUN_IFELSE. - This breaks cross-compilation.

#3 continue using AM_PATH_LIBTASN1.


#5 remove the version requirement and search for used features,
allowing linkage with buggy libtasn1.

cu andreas
The 'Galactic Cleaning' policy undertaken by Emperor Zhark is a personal
vision of the emperor's, and its inclusion in this work does not constitute
tacit approval by the author or the publisher for any such projects,
howsoever undertaken.                                (c) Jasper Ffforde

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