From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mark H Weaver <mhw@netris.org>
Subject: Re: Pass --build=<triplet> to native builds by default?
Date: Sat, 03 Jan 2015 17:15:42 -0500
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To: Ludovic =?utf-8?Q?Court=C3=A8s?= <ludo@gnu.org>
Cc: guix-devel@gnu.org

Mark H Weaver <mhw@netris.org> writes:

> ludo@gnu.org (Ludovic Court=C3=A8s) writes:
>
>> Mark H Weaver <mhw@netris.org> skribis:
>>
>>> It turns out that on ARM systems, the result of 'config.guess' depends
>>> on the result of 'uname -m'.  In other words, details of the kernel (and
>>> perhaps processor?) on the build machine will determine the triplet of
>>> our builds, which in turn may affect what set of instructions is used.
>>
>> Do you know how the =E2=80=98uname -m=E2=80=99 output is used in config.=
guess?  What
>> does it return on ARM?
>
> The output of 'uname -m' becomes the first (cpu) component of the GNU
> triplet.  uname(1) gets its information from the kernel via the uname(2)
> system call.  The field returned by 'uname -m' is described as "Hardware
> identifier".  See <http://man7.org/linux/man-pages/man2/uname.2.html>.
>
> Here's the relevant section of config.guess from gcc-4.8.4:
>
>     arm*:Linux:*:*)
> 	eval $set_cc_for_build
> 	if echo __ARM_EABI__ | $CC_FOR_BUILD -E - 2>/dev/null \
> 	    | grep -q __ARM_EABI__
> 	then
> 	    echo ${UNAME_MACHINE}-unknown-linux-${LIBC}
> 	else
> 	    if echo __ARM_PCS_VFP | $CC_FOR_BUILD -E - 2>/dev/null \
> 		| grep -q __ARM_PCS_VFP
> 	    then
> 		echo ${UNAME_MACHINE}-unknown-linux-${LIBC}eabi
> 	    else
> 		echo ${UNAME_MACHINE}-unknown-linux-${LIBC}eabihf
> 	    fi
> 	fi
> 	exit ;;

I forgot to answer your second question.  On my Novena, 'uname -m'
returns "armv7l".  The problem is this: I suspect that if the build
machine has an armv8 processor, it will return something different like
"armv8l".

      Mark