[PATCH, GCC/ARM] Remove ARMv8-M code for D17-D31

[Thomas Preudhomme]

Hi,

I've now also added a couple more changes:

* size to_clear_bitmap according to maxregno to be consistent with its use
* use directly TARGET_HARD_FLOAT instead of clear_vfpregs


Original message below (ChangeLog unchanged):

Function cmse_nonsecure_entry_clear_before_return has code to deal with
high VFP register (D16-D31) while ARMv8-M Baseline and Mainline both do
not support more than 16 double VFP registers (D0-D15). This makes this
security-sensitive code harder to read for not much benefit since
libcall for cmse_nonsecure_call functions do not deal with those high
VFP registers anyway.

This commit gets rid of this code for simplicity and fixes 2 issues in
the same function:

- stop the first loop when reaching maxregno to avoid dealing with VFP
   registers if targetting Thumb-1 or using -mfloat-abi=soft
- include maxregno in that loop

ChangeLog entry is as follows:

*** gcc/ChangeLog ***

2017-06-13  Thomas Preud'homme  <thomas.preudhomme@arm.com>

	* config/arm/arm.c (arm_option_override): Forbid ARMv8-M Security
	Extensions with more than 16 double VFP registers.
	(cmse_nonsecure_entry_clear_before_return): Remove second entry of
	to_clear_mask and all code related to it.  Replace the remaining
	entry by a sbitmap and adapt code accordingly.

Testing: Testsuite shows no regression when run for ARMv8-M Baseline and
ARMv8-M Mainline.

Is this ok for trunk?

Best regards,

Thomas

On 23/08/17 11:56, Thomas Preudhomme wrote:
> Ping?
> 
> Best regards,
> 
> Thomas
> 
> On 17/07/17 17:25, Thomas Preudhomme wrote:
>> My bad, found an off-by-one error in the sizing of bitmaps. Please find fixed 
>> patch in attachment.
>>
>> ChangeLog entry is unchanged:
>>
>> *** gcc/ChangeLog ***
>>
>> 2017-06-13  Thomas Preud'homme  <thomas.preudhomme@arm.com>
>>
>>      * config/arm/arm.c (arm_option_override): Forbid ARMv8-M Security
>>      Extensions with more than 16 double VFP registers.
>>      (cmse_nonsecure_entry_clear_before_return): Remove second entry of
>>      to_clear_mask and all code related to it.  Replace the remaining
>>      entry by a sbitmap and adapt code accordingly.
>>
>> Best regards,
>>
>> Thomas
>>
>> On 17/07/17 09:52, Thomas Preudhomme wrote:
>>> Ping?
>>>
>>> Best regards,
>>>
>>> Thomas
>>>
>>> On 12/07/17 09:59, Thomas Preudhomme wrote:
>>>> Hi Richard,
>>>>
>>>> On 07/07/17 15:19, Richard Earnshaw (lists) wrote:
>>>>>
>>>>> Hmm, I think that's because really this is a partial conversion.  It
>>>>> looks like doing this properly would involve moving that existing code
>>>>> to use sbitmaps as well.  I think doing that would be better for
>>>>> long-term maintenance perspectives, but I'm not going to insist that you
>>>>> do it now.
>>>>
>>>> There's also the assert later but I've found a way to improve it slightly. 
>>>> While switching to auto_sbitmap I also changed the code slightly to allocate 
>>>> directly bitmaps to the right size. Since the change is probably bigger than 
>>>> what you had in mind I'd appreciate if you can give me an OK again. See 
>>>> updated patch in attachment. ChangeLog entry is unchanged:
>>>>
>>>> 2017-06-13  Thomas Preud'homme  <thomas.preudhomme@arm.com>
>>>>
>>>>      * config/arm/arm.c (arm_option_override): Forbid ARMv8-M Security
>>>>      Extensions with more than 16 double VFP registers.
>>>>      (cmse_nonsecure_entry_clear_before_return): Remove second entry of
>>>>      to_clear_mask and all code related to it.  Replace the remaining
>>>>      entry by a sbitmap and adapt code accordingly.
>>>>
>>>>>
>>>>> As a result I'll let you take the call as to whether you keep this
>>>>> version or go back to your earlier patch.  If you do decide to keep this
>>>>> version, then see the comment below.
>>>>
>>>> Given the changes I'm more happy with how the patch looks now and making it 
>>>> go in can be a nice incentive to change other ARMv8-M Security Extension 
>>>> related code later on.
>>>>
>>>> Best regards,
>>>>
>>>> Thomas
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