Re: [PATCH] rs6000: Compute rop_hash_save_offset for non-Altivec compiles [PR115389]

["Kewen.Lin" <linkw@linux.ibm.com>]

on 2024/6/13 21:24, Peter Bergner wrote:
> On 6/13/24 12:35 AM, Kewen.Lin wrote:
>>> @@ -826,7 +826,14 @@ rs6000_stack_info (void)
>>>  	  info->ehrd_offset -= info->rop_hash_size;
>>>  	}
>>>        else
>>> -	info->ehrd_offset = info->gp_save_offset - ehrd_size;
>>> +	{
>>> +	  info->ehrd_offset = info->gp_save_offset - ehrd_size;
>>> +
>>> +	  /* Adjust for ROP protection.  */
>>> +	  info->rop_hash_save_offset
>>> +	    = info->gp_save_offset - info->rop_hash_size;
>>> +	  info->ehrd_offset -= info->rop_hash_size;
>>> +	}
>>
>> I understand this is just copied from the if arm, but if I read this right, it can be
>> simplified as:
> 
> Ok, I'll retest with that simplification.

Thanks!
>>> +/* { dg-do assemble } */
>>> +/* { dg-options "-O2 -mdejagnu-cpu=power10 -mrop-protect -mno-vsx -mno-altivec -mabi=no-altivec -save-temps" } */
>>
>> I'd expect -mabi=no-altivec is default for -mno-altivec, but specifying it explicitly
>> looks fine to me. :)
> 
> That's what I expected too! :-)  However, I was surprised to learn that -mno-altivec
> does *not* disable TARGET_ALTIVEC_ABI.  I had to explicitly use the -mabi= option to
> expose the bug.

oh, it's surprising, I learn something today! :) I guess it's not intentional but just no
one noticed it, as it seems nonsense to have altivec ABI extension but not using any altivec
features.

BR,
Kewen