Currently, the kernel uses pahole version checking as the way to
determine which BTF encoding features to request from pahole. This
means that such features have to be tied to a specific version and
as new features are added, additional clauses in scripts/pahole-flags.sh
have to be added; for example
if [ "${pahole_ver}" -ge "125" ]; then
extra_paholeopt="${extra_paholeopt} --skip_encoding_btf_inconsistent_proto --btf_gen_optimized"
fi
To better future-proof this process, we can have a catch-all
single "btf_features" parameter that uses a comma-separated list
of encoding options. What makes this better is that any version
of pahole that supports btf_features can accept the option list;
unknown options are silently ignored. However there would be no need
to add additional version clauses beyond
if [ "${pahole_ver}" -ge "126" ]; then
extra_pahole_opt="-j --lang_exclude=rust
--btf_features=encode_force,var,float,decl_tag,type_tag,enum64,optimized,consistent"
fi
Newly-supported features would simply be appended to the btf_features
list, and these would have impact on BTF encoding only if the features
were supported by pahole. This means pahole will not require a version
bump when new BTF features are added, and should ease the burden of
coordinating such changes between bpf-next and dwarves.
Patches 1 and 2 are preparatory work, while patch 3 adds the
--btf_features support. Patch 4 provides a means of querying
the supported feature set since --btf_features will not error
out when it encounters an unrecognized features (this ensures
an older pahole without a requested feature will not dump warnings
in the build log for kernel/module BTF generation).
See [1] for more background on this topic.
[1] https://lore.kernel.org/bpf/CAEf4Bzaz1UqqxuZ7Q+KQee-HLyY1nwhAurBE2n9YTWchqoYLbg@xxxxxxxxxxxxxx/
Alan Maguire (4):
btf_encoder, pahole: move btf encoding options into conf_load
dwarves: move ARRAY_SIZE() to dwarves.h
pahole: add --btf_features=feature1[,feature2...] support
pahole: add --supported_btf_features to display feature support
btf_encoder.c | 8 +--
btf_encoder.h | 2 +-
dwarves.c | 16 ------
dwarves.h | 19 +++++++
man-pages/pahole.1 | 24 +++++++++
pahole.c | 127 ++++++++++++++++++++++++++++++++++++++++-----
6 files changed, 162 insertions(+), 34 deletions(-)
--
2.31.1
