Will binaries built in 10.6 still run in 10.5?

[Nikos Chantziaras]

On 10/04/2010 02:38 PM, Harry van der Wolf wrote:
>>> [...]
> I'm the one who asked about the "Building for different version and/or SDK".
> I build development and release versions of avidemux as a bundle for the
> Mac community and "just" (3 months ago by now) moved to 10.6. I use the
> libraries from macports for the dependencies [...].
> Last week I released another avidemux bundle built with the 10.5 setting
> and until now I did not receive any feedback that it doesn't work on
> 10.5 so I assume it's working correctly.
>
> I simply build with gcc 4.0.1 for i386/ppc and with 4.2.x for 64bit (I
> also build for other OS projects). I have seen many, many errors in all
> kind of libraries/binaries when trying to build 32bit in OSX using
> 4.2.1, so I just stick to 4.0.1. I assume the OSX devs would not use
> 4.0.1 for 32bit if they could use 4.2.1. Why put 2 gcc versions in XCode
> if you could handle it with one. So I assume it's for a good reason.

I'm in a similar situation.  I package an application (that I develop on 
Linux but is portable to OS X and Windows) for Intel as well as PPC 
Macs.  Half of the application (which amounts to about 30MB of 
executable code, all built on my 10.6 installation) is built with 4.2.1 
for both x86 as well as ppc.  And it always worked on PowerPC Macs 
running 10.5 when I compile against the 10.5 SDK.  The other half that 
is not built by me are "Framework" bundles of SDL, libvorbis, etc, 
downloaded from the net.  Those take a lot of space, and I was hoping 
MacPorts could help here.  And it did, at least for the Intel version; 
if I use MacPorts to build the stuff to my liking (disable X11 in SDL, 
formats I don't need in SDL_sound, etc) and link statically, the 
application becomes much smaller, down to about 14MB from the original 
30!  That's half the size.  But unfortunately, the PPC generated code 
crashes at runtime.

Would it help if I installed MacPorts twice, one installation for 
building PPC-only and the other for Intel-only?