[PATCH v7 14/23] aarch64: Mark objects with GCS property note

[Adhemerval Zanella Netto]

On 08/01/25 12:34, Yury Khrustalev wrote:
> On Tue, Jan 07, 2025 at 01:55:50PM -0300, Adhemerval Zanella Netto wrote:
>>
>>
>>>  #define FEATURE_1_AND 0xc0000000
>>>  #define FEATURE_1_BTI 1
>>>  #define FEATURE_1_PAC 2
>>> +#define FEATURE_1_GCS 4
>>>  
>>>  /* Add a NT_GNU_PROPERTY_TYPE_0 note.  */
>>>  #define GNU_PROPERTY(type, value)	\
>>> @@ -103,9 +104,9 @@ strip_pac (void *p)
>>>  /* Add GNU property note with the supported features to all asm code
>>>     where sysdep.h is included.  */
>>>  #if HAVE_AARCH64_BTI && HAVE_AARCH64_PAC_RET
>>
>> Both HAVE_AARCH64_BTI and HAVE_AARCH64_PAC_RET have configure tests 
>> to check if -mbranch-protection={bti,pac-ret} is used.  Why do assume
>> GCS support for this case? Should it have a similar check for
>> -mbranch-protection=gcs?
> 
> The short answer is no, we don't need a similar check for GCS and the way
> it is currenty implement is correct though not ideal. However, I can see
> how this could be confusing.
> 
> First of all, this part only affects hand written assembly and object that
> are compiled from it.
> 
> Secondly, checks for BTI and PAC had been historically added this way and
> this might be amended in the future (e.g. we might want to have BTI always
> enabled by default), but this problem is not relevant for GCS.
> 
> We want GCS markings to be always enabled simply because it doesn't break
> anything and is convenient because we don't want to support every possible
> combination (it would have no practical value). Having GCS added as above
> is the simplest possible solution with no downsides (except for it looking
> a bit confusing at first glance).

Fair enough, should it be enable regardless of HAVE_AARCH64_BTI/HAVE_AARCH64_PAC_RET
then?