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Date: Thu, 26 Jun 2008 23:28:50 +0200
From: Kris Kennaway <kris@FreeBSD.org>
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Cc: FreeBSD Mailing List <freebsd-questions@FreeBSD.org>
Subject: Re: Making World For amd64
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Tim Daneliuk wrote:
> Kris Kennaway wrote:
>> Tim Daneliuk wrote:
>>> Kris Kennaway wrote:
>>>> Tim Daneliuk wrote:
>>>>> Is there anything special one has to do when doing a make world
>>>>> intended for 64-bit FreeBSD or is it sufficient to build the 64-bit
>>>>> kernel and make world as everywhere else?
>>>> The same as everywhere else.
>>>>
>>>> Kris
>>> So, I take it that this means that all the userspace programs, ports,
>>> packages, utilities, etc. do *not* take advantage of the 64-bit
>>> extensions.  That is, only the kernel gets the benefit of the
>>> wider word.  Is that correct?
>>>
>> No, everything is 100% native.
>>
>> Kris
>>
> 
> OK, these may be really stupid questions but:
> 
> 1) How does make world know whether to build 32-bit or 64-bit binaries?

It always uses the native format.  amd64 == 64 bit, i386 == 32 bit

> 2) Can a binary from a 32-bit FreeBSD system be run unmodified on the
>   64-bit system?

Yes, amd64 also builds 32-bit libraries to support this.

> 3) If I reboot with 32-bit or 64-bit kernels, does the system magically
>    somehow make the userland stuff work natively at the word width?
>    If so, how?

You can't run 64 bit binaries on a 32-bit kernel, but you can the other 
way around.

Kris