[U-Boot] Query on CONFIG_SYS_THUMB_BUILD

[Bill Pringlemeir <bpringlemeir@nbsps.com>]

>>> In message <20141119074214.3d414ce6@lilith> you^H^H^H Stefan wrote:

>>>> For -mauto-it, it is not documented in the gas documentation online
>>>> or in my current as' --target-help. I'll dig this deeper today, but
>>>> barring any scream from me, the change above is fine globally in
>>>> U-Boot.

>> On 19 Nov 2014, wd at denx.de wrote:

>>> Apparently this [1] is where it is coming from; no further
>>> documentation there, though.
>>
>>> [1] https://sourceware.org/ml/binutils/2009-05/msg00132.html

> On Wed, 19 Nov 2014 11:31:05 -0500, Bill Pringlemeir

>> I would think that if this worked they would make it automatic and
>> not an option.  Probably this is only in certain binutils/as.
>>
>> With 4.6.3 and 4.9.1 I do not have this option,


On 19 Nov 2014, albert.u.boot at aribaud.net wrote:

> Which option do you mean? -mimplicit-it or -mauto-it?

'-mauto-it' , which I think if it is working correctly would be rolled
into '-mimplicit-it' as it generates better code (for an assembler :).
I followed the thread above and the patch originator says he needs to
fix section issues and the 'command line options' and he would follow up
the proposed patch.

I guess at some version each and every '<inst>xx' was converted to 'it
xx\n<inst>' where <inst> is some conditional instruction.  For the patch
above, '-mauto-it' teaches the assembler to glob them together into
'itet...'  type conditions.  The Thumb2 supports up to four conditions
(and negated condition) instructions.

On my version of the tools (I think it is gcc; but maybe binutils), if I
use '-mauto-it' it gives an unknown option error.  I think that Linux
does a probe of this feature and passes it (-mauto-it) if the assembler
accepts it.  So, if we add to u-boot we should probably take care that
the ARM 'as' can take the option.  I also see posts on the web of people
complaining of this option in other code bases.

Fwiw,
Bill.