eddyz87 added a subscriber: anakryiko.
eddyz87 added a comment.
In D143967#4231746 <https://reviews.llvm.org/D143967#4231746>, @jemarch wrote:
>> eddyz87 added a comment.
>> ...
>> If we consider type tag a qualifier, conceptually it would be simpler
>> if ordering would not matter for it as well, so that the following
>> have identical meaning:
>>
>> - `__tag volatile int`
>> - `volatile __tag int`
>
> Makes sense.
>
> But then I think we should allow the tags to be anywhere in the chain in
> the DWARF, and not necessarily in the qualified type. For example
> given:
>
> typedef const int bar;
> volatile bar __tag1 foo;
>
> The resulting DWARF type chain is:
>
> volatile -> typedef (bar) -> const -> int
>
> IMO we should allow __tag1 to be a child of any of the elements of the
> chain, like:
>
> volatile -> typedef (bar) -> const -> int
> |
> __tag1
>
> or
>
> volatile -> typedef (bar) -> const -> int
> |
> __tag1
>
> or
>
> volatile -> typedef (bar) -> const -> int
> |
> __tag1
>
> or
>
> volatile -> typedef (bar) -> const -> int
> |
> __tag1
>
> would be all accepted and equivalent. Also Faust noted that GCC
> sometimes optimizes out the typedef nodes, so we need to be able to
> place the tags (in the internal representatinos) in the typedef'ed type
> instead.
Well, it's a logical consequence, I guess.
In practice I'm going to emit it like below:
volatile -> const -> int
|
__tag1
But please remember that in BTF it would have to be encoded like this:
__tag1 -> volatile -> const -> int
(that's how kernel expects it, we can change the kernel but will loose
backwards compatibility).
For DWARF -> BTF transformation in `pahole` I will make the necessary
modifications, but BTF might also be emitted C->BPF backend.
@yonghong-song, @anakryiko, what do you think?
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D143967/new/
https://reviews.llvm.org/D143967
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
