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Support parsing bitfields from BTF/DWARF #2505

Merged
merged 5 commits into from
Mar 29, 2023
Merged

Support parsing bitfields from BTF/DWARF #2505

merged 5 commits into from
Mar 29, 2023

Commits on Mar 29, 2023

  1. Let CMake generate BTF data for unit tests 

    This is done similarly to generating mocked DWARF data, using the same
source data.

Requires several utilities: pahole, llvm-objcopy, xxd, nm, awk.

Especially llvm-objcopy may be troublesome as it is required by pahole
but it is often named llvm-objcopy-XX or llvmXX-objcopy where XX is the
LLVM version.  Hence, we set the LLVM_OBJCOPY env variable which pahole
is able to process.

Pahole is not packaged in Alpine 3.12 which is used in embedded CI
tests. Since I was not able to bump Alpine to any newer version that
would have pahole, we build it from source for now.
    @viktormalik
    viktormalik committed Mar 29, 2023
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  2. Refactor work with bitfields 

    Two important refactorings were done:

- Bitfield info is now stored inside Field as std::optional<Bitfield>
  (instead of bool is_bitfield + Bitfield). This is more convenient to
  work with but required some changes, especially to serialization and
  tests.

- Moved algorithm for computing bitfield information from ClangParser to
  the Bitfield class since the same algorithm will be used for
  generating bitfields from BTF and DWARF.

Requires libcereal version >= 1.3.0 (support for std::optional), install
it manually in the Docker image for embedded builds (focal has 1.2.1).
    @viktormalik
    viktormalik committed Mar 29, 2023
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  3. Parse bitfields from BTF 

    Re-using the existing bitfield parsing algorithm (originally from Clang
parser). Add a unit test for bitfield parsing (FieldAnalyser). The test
required to expand the testing BTF data.
    @viktormalik
    viktormalik committed Mar 29, 2023
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  4. Parse bitfields from DWARF 

    Re-using the existing bitfield parsing algorithm.

The problem is that DWARF versions >=4 use a different approach to
represent bitfield offsets from the one used in versions <4 (in
addition, some systems, such as the one in the CI, use the old approach
even for DWARF 4). Hence, we support both approaches. See code comments
for implementation details.

A new unit test for bitfield parsing is added to FieldAnalyser,
supporting both variants of bitfield representation.
    @viktormalik
    viktormalik committed Mar 29, 2023
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  5. Update CHANGELOG (bitfield parsing from BTF/DWARF)

    @viktormalik
    viktormalik committed Mar 29, 2023
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