Re: [PATCH, binutils/ARM] Fix feature checks based on arch value and force review of logic for new arch

[Thomas Preudhomme <thomas dot preudhomme at foss dot arm dot com>]

On Monday 20 June 2016 09:52:25 Thomas Preudhomme wrote:
> On Thursday 16 June 2016 16:02:52 mickael guene wrote:
> > Hi Thomas,
> 
> Hi Mickael,
> 
> >    32-bit BL offset is encoded on 24 bits (with lsb set to zero) and
> > 
> > so biggest value is THM2_MAX_FWD_BRANCH_OFFSET and not
> > THM_MAX_FWD_BRANCH_OFFSET.
> > 
> >    Whereas thumb1 BL offset (two 16 bits instructions, see armv5t) offset
> > 
> > is encoded on 22 bits (with lsb set to zero) and so biggest value is
> > THM_MAX_FWD_BRANCH_OFFSET.
> 
> Yes, the important bit is the note in the description of the BL instruction
> in the ARM Architecture Reference Manual. ARMv6-M, despite not having
> Thumb-2 technology, has an extended range for the BL instruction.
> 
> >    So as now using_thumb2() returns 0 for armv6-m architecture it
> > 
> > generates veneer for branch offset between THM_MAX_FWD_BRANCH_OFFSET
> > and THM2_MAX_FWD_BRANCH_OFFSET whereas it was not the case before
> > your patch.
> 
> Indeed. As you noticed, using_thumb2 is used to control both the
> availability of that extended BL and the availability of nop.w. Therefore I
> think your solution is the right one. I'll create the patch.

Just to let you know that I already got a patch and testing is ongoing (for 
ARMv4T, ARMv6-M and ARMv7-M). I shall have something by tomorrow evening.

Best regards,

Thomas