[OE-core] [PATCH 2/3] Add basic Mips core tune config

[Phil Blundell]

On Tue, 2011-07-26 at 13:44 +0100, Richard Purdie wrote:
> +# MIPS Architecture definition
> +# 12 defined ABIs, all combinations of:
> +# *) Big/Little Endian
> +# *) Hardware/Software Floating Point
> +# *) o32, n32, n64 ABI
> +
> +DEFAULTTUNE ?= "mips"
> +
> +# Endianess
> +TUNEVALID[bigendian] = "Enable big-endian mode"
> +TUNE_CCARGS += "${@bb.utils.contains("TUNE_FEATURES", "bigendian", "-meb", "-mel", d

I've just been trying to do a mips build for the first time since these
patches were landed and I'm a little bit unclear about what the "right"
way to declare endianness is nowadays.

The new tuning system has introduced the idea of endianness as an ABI
tune parameter and, by implication, if I don't have "bigendian" in
TUNE_FEATURES then presumably this is meant to mean little-endian.
However, there seem to be at least some places in OE which are still
expecting endianness to be encoded into TARGET_ARCH, i.e. a
little-endian system would be TARGET_ARCH=mipsel rather than mips. 

Right now, building a little-endian MIPS32 doesn't seem to work either
way around.  If I set TARGET_ARCH=mips and exclude bigendian from
TUNE_FEATURES then (among other issues) uclibc-config.inc decides that
my system is bigendian and sticks -Wl,-EB back into LDFLAGS.
Conversely, if I set TARGET_ARCH=mipsel then I don't get "mips" in
OVERRIDES and I end up with the wrong uClibc.machine and associated
-mips1 lossage.

That latter failure is at least relatively easy to work around and so
that's what I'm doing at the moment.  But I don't know whether this is
the "right" way to proceed or whether TARGET_ARCH is expected to be
endian-agnostic in this newly tuned-up world.

p.