[PATCH dwarves 0/4] Improve BTF concrete function accuracy

This series brings together a few solutions to issues we have
with accuracy of BTF function representation at the binary level.

The first patch detects mismatches between concrete (binary)
and abstract (source-level) function signatures as a means
of either excluding them or providing a "true" function signature.

Patch 2 is from Yonghong's LLVM true function signature series,
and helps for patch 3 which adds GCC true function signature
support for optimized functions; with that support, we use
binary-level signatures for .isra, .constprop functions and
represent them with their "." suffixes as BTF_KIND_FUNC
names.  This allows for fentry attach to such functions, and
the "." suffix is an indicator of signature modification.
The feature is guarded by a default-off BTF feature because
older kernels did not support a "." in a function name.

Patch 4 is Matt's patch to favour the strong function
over the associated weak declaration.  The other patches
are important prerequisites for this as the patch selects
the binary-level function (with a lowpc value), and in
the case of optimized functions we were often selecting
the .isra function with optimized-out parameters.  Because
pahole did not previously detect this correctly we ended
up with functions with signatures having reordered parameters.

Patches 1-3 help avoid this by better detecting optimized-out
function parameters.

With these patches in place, ~20 functions are omitted from
vmlinux BTF; all these are "."-suffixed functions which
we were not noticing had optimized-out parameters.

Experimenting with adding true_signature to BTF features
we end up adding approximately 500 .isra and .constprop
functions to vmlinux BTF.

The true function signature support here will also hopefully
help pave the way for Yonghong's work on the LLVM side.

Alan Maguire (2):
  dwarf_loader/btf_encoder: Detect reordered parameters
  btf_encoder: Add true_signature feature support for "."-suffixed
    functions

Matt Bobrowski (1):
  btf_encoder: Prefer strong function definitions for BTF generation

Yonghong Song (1):
  btf_encoder: Refactor elf_functions__new() with struct btf_encoder as
    argument

 btf_encoder.c  | 142 ++++++++++++++++++++++++++++++++++++++++++-------
 dwarf_loader.c |   5 +-
 dwarves.h      |   3 ++
 pahole.c       |   1 +
 4 files changed, 131 insertions(+), 20 deletions(-)

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2.43.5