On Mon, Sep 16, 2024 at 2:19 AM Eduard Zingerman <eddyz87@xxxxxxxxx> 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@xxxxxxxxx>
> ---
> btf_encoder.c | 59 +++++++++++++++++++++++++++++++++++++--------------
> 1 file changed, 43 insertions(+), 16 deletions(-)
>
LGTM,
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
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!
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