Re: [PATCH dwarves v4 2/6] btf_encoder: use __weak declarations of version-dependent libbpf API

Ihor Solodrai
2025-02-28T19:53:07Z

On 2/28/25 11:46 AM, Ihor Solodrai wrote:
> Instead of compile-time checks for libbpf version, use __weak
> declarations of the required API functions and do runtime checks at
> the call sites. This will help with compatibility when libbpf is
> dynamically linked to pahole [1].
>
> [1] https://lore.kernel.org/dwarves/deff78f8-1f99-4c79-a302-cff8dce4d803@oracle.com/
>
> Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
> ---
> btf_encoder.c | 48 +++++++++++++++++++-----------------------------
> dwarves.h | 11 ++++++++++-
> pahole.c | 2 --
> 3 files changed, 29 insertions(+), 32 deletions(-)
>
> diff --git a/btf_encoder.c b/btf_encoder.c
> index 2bea5ee..12a040f 100644
> --- a/btf_encoder.c
> +++ b/btf_encoder.c
> @@ -34,6 +34,7 @@
> #include <search.h> /* for tsearch(), tfind() and tdestroy() */
> #include <pthread.h>
>
> +#define BTF_BASE_ELF_SEC ".BTF.base"
> #define BTF_IDS_SECTION ".BTF_ids"
> #define BTF_ID_FUNC_PFX "__BTF_ID__func__"
> #define BTF_ID_SET8_PFX "__BTF_ID__set8__"
> @@ -625,29 +626,6 @@ static int32_t btf_encoder__add_struct(struct btf_encoder *encoder, uint8_t kind
> return id;
> }
>
> -#if LIBBPF_MAJOR_VERSION < 1

There is an identical condition in btf_loader.c, however it guards
static functions, for example btf_enum64(). I decided to leave it as
is, although I find it unlikely that someone would use libbpf < 1.0.

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