[PATCH v2 00/10] perf: Refactor/add fallbacks for reading build-id and debuglink

[Ian Rogers <irogers@google.com>]

This cleans up some tech debt mentioned in the thread:
https://lore.kernel.org/lkml/aQt66zhfxSA80xwt@gentoo.org/

The perf tool has fallbacks for objdump but not in the case of
build-id and debuglink reading. Refactor the code so that in the case
of read_build_id it now looks like:

```
...
int filename__read_build_id(const char *filename, struct build_id *bid)
{
	struct kmod_path m = { .name = NULL, };
	char path[PATH_MAX];
	int err, fd;

	if (!filename)
		return -EFAULT;

	if (!is_regular_file(filename))
		return -EWOULDBLOCK;

	err = kmod_path__parse(&m, filename);
	if (err)
		return -1;

	if (m.comp) {
		int error = 0;

		fd = filename__decompress(filename, path, sizeof(path), m.comp, &error);
		if (fd < 0) {
			pr_debug("Failed to decompress (error %d) %s\n",
				 error, filename);
			return -1;
		}
		lseek(fd, 0, SEEK_SET);
		filename = path;
	} else {
		fd = open(filename, O_RDONLY);
		if (fd < 0) {
			pr_debug("Failed to open %s\n", filename);
			return -1;
		}
	}

	err = libbfd__read_build_id(fd, filename, bid);
	if (err == 0)
		goto out;

	err = libelf__read_build_id(fd, filename, bid);
	if (err == 0)
		goto out;

	err = sym_min__read_build_id(fd, filename, bid);
out:
	close(fd);
	if (m.comp)
		unlink(filename);
	return err;
}
...
```

That is what was previously symbol-elf decompression code is now made
common for all cases of reading. The handling of "is_regular_file" is
now common. There is a clear fallback from libbfd to libelf to the
symbol-minimal (sym_min) versions of the functions.

To support this there is refactoring of code into a perf-libelf.c
file, to follow patterns established for the capstone, LLVM and libbfd
code.

v2: Rebase, resolving merge conflict with James' removal of the block
    argument:
    https://lore.kernel.org/lkml/20251121-james-perf-non-block-v1-1-6ab2702ab573@linaro.org/
    Add a patch fixing an issue with return values from
    filename__read_build_id. Some tweaks to the PPC arch__sym_update
    patch commit message and make it 64-bit only. Change the
    sysfs__read_build_id code combining the libelf and minimal
    implementations but avoiding the memory read overhead, avoiding a
    potential buffer overrun if the descsz was particularly large in a
    build ID note, avoid reads and just using seeks.

v1: https://lore.kernel.org/lkml/20251123023225.8069-1-irogers@google.com/

Ian Rogers (10):
  perf symbol: Reduce scope of elf__needs_adjust_symbols
  perf symbol: Reduce scope of arch__sym_update
  perf symbol: Move libelf code to its own file/header
  perf symbol: Remove unused includes
  perf symbol: Move dso__load_bfd_symbols out of symbol.h
  perf symbol: Use fallbacks with filename__read_build_id
  perf symbol: Use fallbacks for filename__read_debuglink
  perf symbol: Make a common sysfs__read_build_id
  perf dso: Move type helpers out of symbol and use fallbacks
  perf symbol: Fix ENOENT case for filename__read_build_id

 tools/perf/arch/powerpc/util/sym-handling.c   |   7 -
 tools/perf/builtin-annotate.c                 |  47 +--
 tools/perf/builtin-buildid-cache.c            |   6 +-
 tools/perf/builtin-c2c.c                      |  58 +--
 tools/perf/builtin-diff.c                     |  22 +-
 tools/perf/builtin-inject.c                   |  19 +-
 tools/perf/builtin-kmem.c                     |  41 ++-
 tools/perf/builtin-kwork.c                    |   9 +-
 tools/perf/builtin-mem.c                      |  16 +-
 tools/perf/builtin-report.c                   |  76 ++--
 tools/perf/builtin-sched.c                    |  50 ++-
 tools/perf/builtin-script.c                   |  89 ++---
 tools/perf/builtin-timechart.c                |  34 +-
 tools/perf/builtin-top.c                      |  85 +++--
 tools/perf/builtin-trace.c                    |  82 ++---
 .../scripts/python/Perf-Trace-Util/Context.c  |  11 +-
 tools/perf/tests/code-reading.c               |   1 +
 tools/perf/tests/hists_cumulate.c             |   1 +
 tools/perf/tests/hists_filter.c               |   1 +
 tools/perf/tests/hists_link.c                 |   1 +
 tools/perf/tests/hists_output.c               |   1 +
 tools/perf/tests/mmap-thread-lookup.c         |   1 +
 tools/perf/tests/pe-file-parsing.c            |   5 +-
 tools/perf/util/Build                         |   6 +-
 tools/perf/util/annotate-data.c               |   7 +-
 tools/perf/util/auxtrace.h                    |   1 +
 tools/perf/util/block-info.c                  |  11 +-
 tools/perf/util/build-id.c                    |  28 +-
 tools/perf/util/callchain.c                   |   1 +
 tools/perf/util/cs-etm.c                      |   1 +
 tools/perf/util/data-convert-json.c           |  30 +-
 tools/perf/util/db-export.c                   |  16 +-
 tools/perf/util/dlfilter.c                    |  11 +-
 tools/perf/util/dlfilter.h                    |   1 +
 tools/perf/util/dso.c                         |  57 +--
 tools/perf/util/event.c                       |  41 ++-
 tools/perf/util/evsel_fprintf.c               |  14 +-
 tools/perf/util/hist.c                        |  29 +-
 tools/perf/util/intel-pt.c                    |  35 +-
 tools/perf/util/kvm-stat.h                    |   5 +-
 tools/perf/util/libbfd.c                      |   9 +-
 tools/perf/util/libbfd.h                      |  12 +-
 tools/perf/util/machine.c                     |  34 +-
 tools/perf/util/perf-libelf.c                 | 235 ++++++++++++
 tools/perf/util/perf-libelf.h                 |  58 +++
 tools/perf/util/print_insn.c                  |  14 +-
 tools/perf/util/probe-event.c                 |   1 +
 tools/perf/util/probe-finder.c                |   1 +
 .../util/scripting-engines/trace-event-perl.c |   1 +
 .../scripting-engines/trace-event-python.c    |   1 +
 tools/perf/util/symbol-elf.c                  | 338 +-----------------
 tools/perf/util/symbol-minimal.c              | 166 +++++----
 tools/perf/util/symbol-minimal.h              |  13 +
 tools/perf/util/symbol.c                      | 107 +++++-
 tools/perf/util/symbol.h                      |  44 +--
 tools/perf/util/symbol_fprintf.c              |   1 +
 tools/perf/util/thread-stack.c                |  12 +-
 tools/perf/util/thread.c                      |  18 +-
 tools/perf/util/unwind-libdw.c                |  15 +-
 59 files changed, 1079 insertions(+), 958 deletions(-)
 create mode 100644 tools/perf/util/perf-libelf.c
 create mode 100644 tools/perf/util/perf-libelf.h
 create mode 100644 tools/perf/util/symbol-minimal.h

-- 
2.52.0.158.g65b55ccf14-goog