[PATCH v9 0/3] Capstone/llvm dlopen support

[Ian Rogers <irogers@google.com>]

Linking against libcapstone and libLLVM can be a significant increase
in dependencies and file size if building statically. The dependencies
are also quite cumbersome if bringing perf into a distribution. For
something like `perf record` the disassembler and addr2line
functionality of libcapstone and libLLVM won't be used. These patches
support dynamically loading these libraries using dlopen and then
calling the appropriate functions found using dlsym. Using dlopen
allows libcapstone and libLLVM to be installed separately to perf and
when that's done the performance will improve as separate commands for
objdump and addr2line won't be invoked.

The patch series adds perf_ variants of the capstone/llvm functions
that will either directly call the function or (NO_CAPSTONE=1 and
NO_LIBLLVM=1 cases) use dlopen/dlsym to discover and then call the
function. To support the function signatures when
HAVE_LIBCAPSTONE_SUPPORT and HAVE_LIBLLVM_SUPPORT aren't defined
prototypes generated using pahole are given. This avoids requiring
libcapstone or libLLVM for the sake of the header files. It also
avoids having a build where neither dlopen or dynamic linking against
libcapstone or libLLVM is supported. There are other possibilities in
how to organize this, but the chosen approach was done so for the
simplicity and cleanliness of the code.

The addr2line LLVM functionality is written in C++. To avoid linking
against libLLVM for this, a new LIBLLVM_DYNAMIC option is added where
the C++ code with the libLLVM dependency will be built into a
libperf-llvm.so and that dlsym-ed and called against. Ideally LLVM
would extend their C API to avoid this.

v9: Rebase.
v8: Rebase down to 3 patches. Update commit and cover messages.
v7: Refactor now the first 5 patches, that largely moved code around,
    have landed. Move the dlopen code to the end of the series so that
    the first 8 patches can be picked improving capstone/LLVM support
    without adding the dlopen code. Rename the cover letter and
    disassembler cleanup patches.
v6: Refactor the libbfd along with capstone and LLVM, previous patch
    series had tried to avoid this by just removing the deprecated
    BUILD_NONDISTRO code. Remove the libtracefs removal into its own
    patch.
v5: Rebase and comment typo fix.
v4: Rebase and addition of a patch removing an unused struct variable.
v3: Add srcline addr2line fallback trying LLVM first then forking a
    process. This came up in conversation with Steinar Gunderson
    <sesse@google.com>.
    Tweak the cover letter message to try to address Andi Kleen's
    <ak@linux.intel.com> feedback that the series doesn't really
    achieve anything.
v2: Add mangling of the function names in libperf-llvm.so to avoid
    potential infinite recursion. Add BPF JIT disassembly support to
    LLVM and capstone. Add/rebase the BUILD_NONDISTRO cleanup onto the
    series from:
    https://lore.kernel.org/lkml/20250111202851.1075338-1-irogers@google.com/
    Some other minor additional clean up.

Ian Rogers (3):
  perf capstone: Support for dlopen-ing libcapstone.so
  perf llvm: Support for dlopen-ing libLLVM.so
  perf llvm: Mangle libperf-llvm.so function names

 tools/perf/Makefile.config         |  13 ++
 tools/perf/Makefile.perf           |  24 ++-
 tools/perf/tests/make              |   2 +
 tools/perf/util/Build              |   2 +-
 tools/perf/util/capstone.c         | 285 +++++++++++++++++++++++++----
 tools/perf/util/llvm-c-helpers.cpp | 120 +++++++++++-
 tools/perf/util/llvm-c-helpers.h   |  24 ++-
 tools/perf/util/llvm.c             | 273 ++++++++++++++++++++++++---
 8 files changed, 660 insertions(+), 83 deletions(-)

-- 
2.52.0.457.g6b5491de43-goog