Re: [PATCH v2 dwarves] btf: Remove ftrace filter

[Jiri Olsa <jolsa@redhat.com>]

On Thu, May 06, 2021 at 01:56:22PM -0700, Martin KaFai Lau wrote:
> BTF is currently generated for functions that are in ftrace list
> or extern.
> 
> A recent use case also needs BTF generated for functions included in
> allowlist.  In particular, the kernel
> commit e78aea8b2170 ("bpf: tcp: Put some tcp cong functions in allowlist for bpf-tcp-cc")
> allows bpf program to directly call a few tcp cc kernel functions. Those
> kernel functions are currently allowed only if CONFIG_DYNAMIC_FTRACE
> is set to ensure they are in the ftrace list but this kconfig dependency
> is unnecessary.
> 
> Those kernel functions are specified under an ELF section .BTF_ids.
> There was an earlier attempt [0] to add another filter for the functions in
> the .BTF_ids section.  That discussion concluded that the ftrace filter
> should be removed instead.
> 
> This patch is to remove the ftrace filter and its related functions.
> 
> Number of BTF FUNC with and without is_ftrace_func():
> My kconfig in x86: 40643 vs 46225
> Jiri reported on arm: 25022 vs 55812
> 
> [0]: https://lore.kernel.org/dwarves/20210423213728.3538141-1-kafai@fb.com/
> 
> Cc: Andrii Nakryiko <andrii@kernel.org>
> Cc: Jiri Olsa <jolsa@kernel.org>
> Signed-off-by: Martin KaFai Lau <kafai@fb.com>
> ---
> v2: Remove sym_sec_idx, last_idx, and sh. (Jiri Olsa)

Acked-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka