Re: Pass --build=<triplet> to native builds by default?

[Mark H Weaver]

address@hidden (Ludovic Courtès) writes:

> Mark H Weaver <address@hidden> 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 ‘uname -m’ 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:

--8<---------------cut here---------------start------------->8---
    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 ;;
--8<---------------cut here---------------end--------------->8---

     Mark