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

[Richard Earnshaw]

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.

R.