[PATCH v8 04/19] gas: implement parsing of object attributes v2

[Jan Beulich]

On 14.08.2025 17:29, Matthieu Longo wrote:
> On 2025-08-06 16:20, Richard Earnshaw wrote:
>> On 06/08/2025 16:05, Jan Beulich wrote:
>>> On 06.08.2025 16:02, Matthieu Longo wrote:
>>>> On 2025-07-31 15:40, Jan Beulich wrote:
>>>>> On 15.07.2025 13:39, Matthieu Longo wrote:
>>>>>> The usage of those directives will error if the following requirements
>>>>>> are breached:
>>>>>> - If the subsection X has been previously declared, the 
>>>>>> comprehension and
>>>>>>     encoding parameters of the current .aeabi_subsection that 
>>>>>> redeclares X
>>>>>>     have to match with the previous declaration.
>>>>>
>>>>> If I'm reading things right, such a re-declaration still needs to 
>>>>> provide
>>>>> not only the name, but also "comprehension" and encoding. Just for 
>>>>> it to
>>>>> be checked against the earlier decl. As with ordinary sections, I think
>>>>> it would be nice if an "incomplete" re-decl would be accepted.
>>>>>
>>>>
>>>> Unlike code where there is a genuine usecase of switching to and from
>>>> sections, all the build attributes are in a file scope so there is not
>>>> really much need to split them up. For instance, GCC on AArch64 targets
>>>> will dump them all in one chunk.
>>>> No strong opinion against the idea, so I don't mind adding it if you
>>>> think that it would be valuable for users.
>>>>
>>>> NB: This would require amending the spec, and discussing it with LLVM.
>>>
>>> Well, I don't know how things will typically look in assembly files not
>>> produced by a compiler or alike. If "re-declarations" aren't expected to
>>> be common, perhaps leave as is. Question then is whether to permit
>>> "re-declarations" at all; disallowing them would simplify a few things.
>>>
>>
>> I wouldn't expect a compiler to need to do redeclarations, but I could 
>> envisage a use case for this when using include files to build up a 
>> file.  In that case, I'd expect the attributes to be stand-alone and add 
>> the attributes specific to each hunk.  If you wanted to have it work 
>> where only the first specification of a section defined the flags, you'd 
>> end up either with a pre-declaration of the section, or having some 
>> weird constraint on include order.
>>
>> So I certainly think we need checking of the headers, but perhaps we'd 
>> also want checking of the added attributes as well (unless gas were to 
>> be able to merge re-declarations of a single attribute): for example, 
>> changing an attribute value from 3 to 2 might be completely incorrect, 
>> but keeping 3 might not be correct either - it depends very much on the 
>> context.
> 
> With the current implementation, gas raises an error if an attribute is 
> redeclared with a different value.
> Merging would be the ideal, but since there is no use case for it now, 
> could we delay the merge implementation to when a real use case will 
> emerge ?

I guess that's going to be okay. I'd like to ask though that you mention
the aspect in the description then.

Jan