Re: [PATCH 1/3] Add ARM tune file overhaul based largely on work from Mark Hatle

[Mark Hatle <mark.hatle@windriver.com>]

On 7/27/11 2:31 PM, Phil Blundell wrote:
> On Wed, 2011-07-27 at 12:19 -0500, Mark Hatle wrote:
>> On 7/27/11 10:25 AM, Phil Blundell wrote:
>>> On Wed, 2011-07-27 at 09:58 -0500, Mark Hatle wrote:
>>>> For the tune names..  armv5 means I want classic ARM instructions, while armv5t
>>>> means I was thumb instructions.
>>>>
>>>> So armv5 and armv5t are distinct in the contents of the tunings.
>>>
>>> Ah, I see.  Does that go for v4t too?  I can imagine cases where you
>>> would want to say "select the v4T ISA but generate ARM code not Thumb".
>>
>> Yes, for all of them, the TUNENAME selects the features that you want to use to
>> compile, and suggests the other information like compatible architectures.
>>
>> In the case where you want to build primarily one, and optionally the other the
>> tunename makes it easy..
>>
>> Say you want all of your system thumb, except for a few specific programs..
>>
>> TUNENAME = "armv4t"
>>
>> TUNENAME_pn-mysql = "armv4"
>>
>> In the opposite case, where you want everything ARM, except for a few thumb:
>>
>> TUNENAME = "armv7"
>> TUNENAME_pn-bash = "armv7t"
> 
> I'm not quite sure that this answers the question I was trying to ask.
> 
> The thing about v4/v4T is that, unlike later versions of the
> architecture, plain v4 doesn't include the BX instruction.  So, if you
> want your code to be interworking-capable without requiring linker
> shims, you need to specify -march=armv4t (and -mthumb-interwork) even
> for CUs that you want to compile as ARM code.
> 
> If the architecture name implies the execution state then it doesn't
> appear as though there is going to be any way to select -march=armv4t
> without also selecting -mthumb, which would make it impossible to build
> interworking-capable ARM-state code for v4T.

It was my understanding that interwork was always enabled these days.  Does
interworking require a thumb compatible arm core?

--Mark

>> So then the question is.. with OE-core and core based distros.. are there enough
>> armv5 (w/ or w/o e) left to justify having both?  If not.. then we select the
>> one with the 'e' since it's more common.
> 
> I'm not aware of anybody using a non-e ARMv5 with OE at all.  The two
> most common v5-class implementations, by some margin I think, are the
> ARM9x6 family and Xscale, and all of those are at least v5TE. 
> 
> p.
> 
> 
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