On Mar 20, 2012, at 10:56 AM, Ralf Corsepius wrote:

> On 03/20/2012 10:01 AM, Tristan Gingold wrote:
>> Hi,
>> I am starting to build fortran for VMS.
>> The first serious issue was with libgfortran/configure.  It checks for 
>> several math functions, but directly in libm using AC_CHECK_LIB.
>> But there is on such things as libm on VMS systems (thus requiring to define 
>> MATH_LIBRARY as "").  Therefore all these tests fail,
>> resulting in a failure during libgfortran build.
>> I think the best way to test for the math function is to use AC_CHECK_DECLS 
>> as hinted by the autoconf manual
>> (cf the AC_CHECK_DECLS example in 
>> http://www.gnu.org/software/autoconf/manual/autoconf.html
>>          AC_CHECK_DECLS([j0], [], [], [[#include<math.h>]])
>>          AC_CHECK_DECLS([[basename(char *)], [dirname(char *)]])
>> )
>> but I am not an autoconf expert.
>> I think that this change makes the AIX specific check for __clog obsolete, 
>> but I haven't removed it.
>> With this change I was able to cross build libgfortran for VMS (ia64 and 
>> alpha).
>> I have also bootstrapped gcc for x86_64-darwin, without fortran regressions.
>> Ok for trunk ?
> IMO, no.
> What you are doing here is to replace checks, which check for presence of a 
> symbol in a library (e.g. cos in libm.*) by checks for presence of a symbol's 
> declaration inside of a header.
> This is something entirely different (This also reflects in AC_CHECK_DECL by 
> default providing HAVE_DECL_XXX defines).

Ah, indeed.  I missed that.

> Also note that it's not uncommon to have declarations inside of headers, 
> which are not present inside of a library.

So, I should use AC_LINK_IFELSE instead, shouldn't I ?


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