Re: [PATCH 3/3] glib.inc: limit ARM_INSTRUCTION_SET over-rides to armv4/armv5

[Martin Jansa <martin.jansa@gmail.com>]

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On Thu, Mar 03, 2016 at 01:02:35PM +0000, Phil Blundell wrote:
> On Wed, 2016-01-27 at 15:28 -0800, Andre McCurdy wrote:
> > -ARM_INSTRUCTION_SET = "arm"
> > +ARM_INSTRUCTION_SET_armv4 = "arm"
> > +ARM_INSTRUCTION_SET_armv5 = "arm"
> 
> Although I agree that this is a net improvement over the old code in
> almost all cases, this patch is not quite right.  The reason for the
> original override is that there is assembler code in glib which won't
> compile as Thumb-1 (but is ok in Thumb-2).  Thumb-2 is only available
> in ARMv6T2 and newer architectures so with your patch it looks like
> compilation on arm1136jf-s (which is ARMv6 not ARMv6T2) would now fail.

If the MACHINE doesn't have thumb in TUNE_FEATURES (for selected
DEFAULTTUNE) won't use -mthumb, so building on ARMv6 shouldn't fail
or I didn't get your point.

> I recommend that we either:
> 
> 1. Introduce a new, explicit "thumb1" override which can be enabled by
> the appropriate arch-arm*.inc files, and make all the appropriate
> recipes set ARM_INSTRUCTION_SET based on that; or
> 
> 2. Introduce a new thumb1-compatible.inc file which contains lines like
> 
> ARM_INSTRUCTION_SET_glib-2.0 = "arm"
> 
> and let distros which want to support older ARMs and enable Thumb
> include that file; or
> 
> 3. Take the view that it's now nearly fifteen years since Thumb-2 was
> introduced, OE-core no longer needs to pander explicitly to Thumb-1,
> and we should just remove all this scar tissue entirely.  Distros that
> do want to target Thumb-1 can still maintain the appropriate
> compatibility stuff (which is probably only a dozen lines or so) for
> themselves.

Except that oe-core still contains qemuarm which is armv5t and almost 
nobody is building it with thumb enabled in DISTRO config. I'm regularly
asking it to be enabled on autobuilder, but without luck:
https://bugzilla.yoctoproject.org/show_bug.cgi?id=7717

> Personally I would favour #3. :-)
> 
> p.
> 
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-- 
Martin 'JaMa' Jansa     jabber: Martin.Jansa@gmail.com

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