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From: Jiri Olsa <jolsa@kernel.org>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: dwarves@vger.kernel.org, bpf@vger.kernel.org,
	Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andriin@fb.com>, Yonghong Song <yhs@fb.com>,
	Hao Luo <haoluo@google.com>, "Frank Ch. Eigler" <fche@redhat.com>,
	Mark Wielaard <mjw@redhat.com>
Subject: [PATCHv3 0/3] pahole/kernel: Workaround dwarf bug for function encoding
Date: Wed,  4 Nov 2020 22:59:20 +0100	[thread overview]
Message-ID: <20201104215923.4000229-1-jolsa@kernel.org> (raw)

hi,
because of gcc bug [1] we can no longer rely on DW_AT_declaration
attribute to filter out declarations and end up with just
one copy of the function in the BTF data.

It seems this bug is not easy to fix, but regardless if the
it's coming soon, it's probably good idea not to depend so
much only on dwarf data and make some extra checks.

Thus for function encoding we are now doing following checks:
  - argument names are defined for the function
  - there's symbol and address defined for the function
  - function address belongs to ftrace locations (new in v2)
  - function is generated only once

v3 changes:
  - added Hao's ack for patch 1
  - fixed realloc memory leak [Andrii]
  - fixed addrs_cmp function [Andrii]
  - removed SET_SYMBOL macro [Andrii]
  - fixed the 'valid' function logic
  - added .init.bpf.preserve_type check
  - added iterator functions to new kernel section
    .init.bpf.preserve_type [Yonghong]

v2 changes:
  - add check ensuring functions belong to ftrace's mcount
    locations, this way we ensure to have in BTF only
    functions available for ftrace - patch 2 changelog
    describes all details
  - use collect* function names [Andrii]
  - use conventional size increase in realloc [Andrii]
  - drop elf_sym__is_function check
  - drop patch 3, it's not needed, because we follow ftrace
    locations

thanks,
jirka


[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97060


             reply	other threads:[~2020-11-04 22:00 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-04 21:59 Jiri Olsa [this message]
2020-11-04 21:59 ` [PATCH 1/3] bpf: Move iterator functions into special init section Jiri Olsa
2020-11-05  1:01   ` Song Liu
2020-11-04 21:59 ` [PATCH 2/3] btf_encoder: Move find_all_percpu_vars in generic collect_symbols Jiri Olsa
2020-11-05 19:34   ` Andrii Nakryiko
2020-11-04 21:59 ` [PATCH 3/3] btf_encoder: Change functions check due to broken dwarf Jiri Olsa
2020-11-05 19:52   ` Andrii Nakryiko
2020-11-05 22:56     ` Jiri Olsa

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