Re: architecture-independent GNAT project files?

["Björn Persson" <bjorn@xn--rombobjrn-67a.se>]

Dmitry A. Kazakov wrote:

> On Mon, 27 Apr 2009 09:32:29 +0200, Bj�rn Persson wrote:
> 
>> When I write GNAT project files for shared libraries I find that I have
>> to hardcode the paths to some architecture-specific directories. 32-bit
>> libraries are in /usr/lib/ while 64-bit libraries are in /usr/lib64/, and
>> I would like to have a single project file that works for both cases.
> 
> The way I am using is to have a platform variable in the project file:
> 
>    type Platform_Type is ("x86_Windows", "x86_VxWorks");
>    Platform : Platform_Type := external ("Platform", "x86_Windows");
> 
> and then somewhere later
> 
>    case Platform is
>       when "x86_Windows" =>
>          for Source_Dirs use "os/Windows/i586" & ...;
>       when "x86_VxWorks" =>
>          for Source_Dirs use "os/vxworks/i586" & ...;
>    end case;
> 
> then same for library things etc.

The analog for my case would be:

   type Architecture is ("i386", "x86_64");
   Target : Architecture := external ("Target", "i386");

The problem with that is of course that on x86_64 systems the default will
almost always be wrong, and if I set the default to x86_64 it will be wrong
on i386 systems.

>> The way to find out the architecture of a Unix-like system appears to be
>> to invoke uname, but GNAT project files don't seem to have a shell-out
>> feature. As far as I can see in the manual the only ways they can get
>> input is by environment variables and command line parameters. I don't
>> suppose Gnatmake provides some variable to project files that shows what
>> the architecture is?
> 
> I don't know if it has, but if any, how that is supposed to work for cross
> platform developing?

The cross-compiler would know its target platform and would assign that
value to the hypothetical variable. The project file would then select the
right library directories for that platform.

Such a feature, if done right, could make it possible to write project files
that would work for anything from ARM to Itanium, but I wasn't planning to
do that. I'm satisfied if I can support a multilib environment so that i386
libraries will be selected if someone uses the -m32 parameter on an x86_64
platform. For true cross-compilation I guess the cross-compiler will
normally have a completely separate set of libraries, including a separate
project file directory.

-- 
Bj�rn Persson
PGP key A88682FD