[ARM] How to query gas for target properties?

[ARM] How to query gas for target properties?

[Christophe Lyon]

Hi,

I'd like to write an assembly code fragment with some parts conditional
to some target properties.
For instance, on ARM, I'd like to know if the target has the Neon
extension, ie gas if gas was invoked with -mfpu=neon.

I have been able to perform some other conditions (eg architecture
variant) through cpp, but I have found nothing enabling to know that
-mfpu=neon was used.

Any trick?

Thanks

Re: [ARM] How to query gas for target properties?

[Nick Clifton]

Hi Christophe,

> I'd like to write an assembly code fragment with some parts conditional
> to some target properties.
> For instance, on ARM, I'd like to know if the target has the Neon
> extension, ie gas if gas was invoked with -mfpu=neon.
>
> I have been able to perform some other conditions (eg architecture
> variant) through cpp, but I have found nothing enabling to know that
> -mfpu=neon was used.

Probably the easiest method would be to write the code in C as extended 
assembler statements and check for the presence of the __ARM_NEON__ 
preprocessor variable.

Cheers
   Nick

Re: [ARM] How to query gas for target properties?

[Christophe Lyon]

On 27.10.2010 15:45, Nick Clifton wrote:
> Hi Christophe,
> 
>> I'd like to write an assembly code fragment with some parts conditional
>> to some target properties.
>> For instance, on ARM, I'd like to know if the target has the Neon
>> extension, ie gas if gas was invoked with -mfpu=neon.
>>
>> I have been able to perform some other conditions (eg architecture
>> variant) through cpp, but I have found nothing enabling to know that
>> -mfpu=neon was used.
> 
> Probably the easiest method would be to write the code in C as extended 
> assembler statements and check for the presence of the __ARM_NEON__ 
> preprocessor variable.
> 


Thanks for you answer, that's what I had ended up doing.

My 1st attempts at using this macro failed because I didn't use
-mhardfp; I don't know why -mfpu=neon isn't sufficient to get
__ARM_NEON__ defined by GCC.

Thanks
Christophe.

Re: [ARM] How to query gas for target properties?

[Ramana Radhakrishnan]

>
> Thanks for you answer, that's what I had ended up doing.
>
> My 1st attempts at using this macro failed because I didn't use
> -mhardfp; I don't know why -mfpu=neon isn't sufficient to get
> __ARM_NEON__ defined by GCC.

You need to use -mfloat-abi=softfp or -mfloat-abi=hard ? If
-mfloat-abi isn't softfp or hard GCC won't generate any Neon code
despite there being a -mfpu=neon and hence the macro need not be
defined.


cheers
Ramana


>
> Thanks
> Christophe.
>