Re: [PATCH dwarves v1] pahole: generate "bpf_fastcall" decl tags for eligible kfuncs

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Fri, Sep 27, 2024 at 02:52:24PM -0700, Andrii Nakryiko wrote:
> On Mon, Sep 16, 2024 at 2:19 AM Eduard Zingerman <eddyz87@gmail.com> wrote:
> >
> > For kfuncs marked with KF_FASTCALL flag generate the following pair of
> > decl tags:
> >
> >     $ bpftool btf dump file vmlinux
> >     ...
> >     [A] FUNC 'bpf_rdonly_cast' type_id=...
> >     ...
> >     [B] DECL_TAG 'bpf_kfunc' type_id=A component_idx=-1
> >     [C] DECL_TAG 'bpf_fastcall' type_id=A component_idx=-1
> >
> > So that bpftool could find 'bpf_fastcall' decl tag and generate
> > appropriate C declarations for such kfuncs, e.g.:
> >
> >     #ifndef __VMLINUX_H__
> >     #define __VMLINUX_H__
> >     ...
> >     #define __bpf_fastcall __attribute__((bpf_fastcall))
> >     ...
> >     __bpf_fastcall extern void *bpf_rdonly_cast(...) ...;
> >
> > For additional information about 'bpf_fastcall' attribute,
> > see the following commit in the LLVM source tree:
> >
> > 64e464349bfc ("[BPF] introduce __attribute__((bpf_fastcall))")
> >
> > And the following Linux kernel commit:
> >
> > 52839f31cece ("Merge branch 'no_caller_saved_registers-attribute-for-helper-calls'")
> >
> > Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
> > ---
> >  btf_encoder.c | 59 +++++++++++++++++++++++++++++++++++++--------------
> >  1 file changed, 43 insertions(+), 16 deletions(-)
> >
> 
> LGTM,
> 
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
> 
> Arnaldo, can you please take a look and if everything seems sane apply
> it to pahole master, so it's easier to use it locally? Thanks!

Minor clash with Alan's

Fixes: 5205d02d8e84a775 ("btf_encoder: record BTF-centric function state instead of DWARF-centric")

Fixed up, testing.

- Arnaldo