On Thursday, August 11, 2011 01:29:38 PM Phil Blundell wrote:

On Thu, 2011-08-11 at 13:08 +0100, Richard Purdie wrote:

quoted

On Thu, 2011-08-11 at 12:25 +0100, Phil Blundell wrote:

quoted

On Tue, 2011-07-26 at 13:44 +0100, Richard Purdie wrote:

quoted

+# 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.

You sound like you're doing this backwards. Pick a tune that either sets
TUNE_FEATURES to either contain or not contain "bigendian". TARGET_ARCH
then should get set appropriately and things that look at TARGET_ARCH
should work as before.

Ultimately we might want to consider if things like siteconfig should
use TUNE_FEATURES rather than TARGET_ARCH but it should work as things
stand now...

Okay.  So, if I let arch-mips.inc set TARGET_ARCH for itself then it
picks "mipsel", which is the second case I mentioned above and leads to
the -mips1 failure.  I guess this means that either uclibc's usage of
overrides needs fixing, or arch-mips ought to be putting "mips" into
${OVERRIDES}.

uclibc's configuration can now be simplified a bit with new tune files
right now it uses target arch heavily.

More generally, it seems as though having TARGET_ARCH in ${OVERRIDES} is
probably going to be fairly useless if that value now includes all the
decorations for ABI features, since it is going to be hard/impossible to
get it to match reliably.

Does the new tune model provide any variable which represents the
underlying CPU architecture ("arm", "mips")?  That seems to be what's
really wanted in almost all the cases where TARGET_ARCH is being used as
an OVERRIDE.

yeah I think major cpu architecture would be nice to have in overrides
e.g. mips for mipseb and mipsel. We dont need endianness info since we
can deduce that from tune features in todays setup.

p.



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