On Tue, 2025-02-18 at 20:36 -0800, Eduard Zingerman wrote:
> On Wed, 2025-02-12 at 12:15 -0800, Ihor Solodrai wrote:
>
> [...]
>
> > diff --git a/btf_encoder.c b/btf_encoder.c
> > index 965e8f0..3cec106 100644
> > --- a/btf_encoder.c
> > +++ b/btf_encoder.c
>
> [...]
>
> > +static int btf__tag_bpf_arena_ptr(struct btf *btf, int ptr_id)
> > +{
> > + const struct btf_type *ptr;
> > + int tagged_type_id;
> > +
> > + ptr = btf__type_by_id(btf, ptr_id);
> > + if (!btf_is_ptr(ptr))
> > + return -EINVAL;
> > +
> > + tagged_type_id = btf__add_type_attr(btf, BPF_ARENA_ATTR, ptr->type);
> > + if (tagged_type_id < 0)
> > + return tagged_type_id;
> > +
> > + return btf__add_ptr(btf, tagged_type_id);
> > +}
>
> I might be confused, but this is a bit strange.
> The type constructed here is: ptr -> type_tag -> t.
> However, address_space is an attribute of a pointer, not a pointed type.
> I think that correct sequence should be: type_tag -> ptr -> t.
> This would make libbpf emit C declaration as follows:
>
> void * __attribute__((address_space(1))) ptr;
>
> Instead of current:
>
> void __attribute__((address_space(1))) * ptr;
>
> clang generates identical IR for both declarations:
>
> @ptr = dso_local global ptr addrspace(1) null, align 8
>
> Thus, imo, this function should be simplified as below:
>
> static int btf__tag_bpf_arena_ptr(struct btf *btf, int ptr_id)
> {
> const struct btf_type *ptr;
>
> ptr = btf__type_by_id(btf, ptr_id);
> if (!btf_is_ptr(ptr))
> return -EINVAL;
>
> return btf__add_type_attr(btf, BPF_ARENA_ATTR, ptr_id);
> }
>
> [...]
>
Ok, this comment can be ignored.
The following C code:
int foo(void * __attribute__((address_space(1))) ptr) {
return ptr != 0;
}
does not compile, with the following error reported:
test3.c:1:49: error: parameter may not be qualified with an address space
1 | int foo(void *__attribute__((address_space(1))) ptr) {
|
While the following works:
int foo(void __attribute__((address_space(1))) *ptr) {
return ptr != 0;
}
With the following IR generated:
define dso_local i32 @foo(ptr addrspace(1) noundef %0) #0 { ... }
Strange.
