Re: [gentoo-user] cross-compile attempt

[Mick <michaelkintzios@gmail.com>]

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On Sunday 31 Jul 2016 23:18:00 Andrew Savchenko wrote:
> On Sun, 31 Jul 2016 19:40:37 +0100 Mick wrote:
> > Hi All,
> > 
> > I am dipping my toe into cross-compile territory, in order to build i686
> > binaries for a 32bit box, which is too old to do its own emerges.  I am
> > using an amd64 box which is significantly faster to do all the heavy
> > lifting and started applying this page:
> > 
> > https://wiki.gentoo.org/wiki/Embedded_Handbook/General/Creating_a_cross-co
> > mpiler
> > 
> > which I followed up with:
> > 
> > https://wiki.gentoo.org/wiki/Cross_build_environment
> 
> And here comes this misconception again... Please, tell me, why on
> the earth cross-compiling is needed for amd64 to produce i686
> binaries?!

I thought it did.  From what you're saying I got this wrong.  When I read the 
first use case bullet point, on the 2nd URL above, I thought I had arrived at 
the right place.  :-/


> amd64 CPU _natively_ supports x86 instructions, amd64 kernel
> natively supports x86 code (this can be disabled during kernel
> config, but usually it isn't), amd64 gcc *can* produce x86 binaries.

I thought amd64 can run x86 binaries, but I wasn't aware that it can compile 
them too, or what is needed to achieve this.  My knowledge on gcc is pretty 
much minimal.  I did search the Wiki, gentoo.org and Google for it, but all I 
could come across was cross-compiling.


> There are two ways to help older x86 boxes to build packages faster:
> 
> 1. Set up distcc to produce x86 code on your amd64 processors. Just
> add -m32 to your *FLAGS.

I read somewhere in these unsuccessful searches of mine that distcc is 
deprecated and it is better to use cross-compiling instead ... 


> 2. Copy old box system to a chroot dir on amd64. Run setarch i686
> and chroot to that directory, and build 32-bit packages as usual!
> There are two ways to deliver them:
> 
> 2.a. Generate binary packages on new box and install them on old
> boxes.

OK, I'll uninstall crossdev and try 2.a in the first instance.  Is there a Wiki 
page explaining what parts of the x86 system are needed to carry across to the 
amd64 guest_root_fs?  I wouldn't think I will need the whole x86 fs?  Anything 
else I need to pay attention to?


> 2.b. Instead of copying old box's root, mount it over NFS.

I'll look into this later, after I get 2.a going.
 

> I'm currently using 1, but planning to switch to 2.a, because
> distcc can't help with everything (execution of java, python,
> autotools and other stuff can't be helped with distcc).
> 
> I used 2.b earlier on very old box (it is dead now).
> 
> 3. Well, one can do full cross-compilation as you proposed, but
> this is ridiculous. Cross-compilation is always a pain and if it
> can be avoided, it should be avoided.

Thanks for this advice.  I am not particularly interested to use crossdev if 
it is not the best suited tool for the job, but I wasn't aware of the 
alternatives you suggested and haven't as yet found any HOWTOs on it.

-- 
Regards,
Mick

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