[PATCH v6 0/8] perf: Support searching local debugging vdso or specify vdso path in cmdline

[Changbin Du]

The vdso dumped from process memory (in buildid-cache) lacks debugging
info. To annotate vdso symbols with source lines we need a debugging
version.

For x86, we can find them from your local build as
'arch/x86/entry/vdso/vdso{32,64}.so.dbg'. Or they may resides in
'/lib/modules/<version>/vdso/vdso{32,64}.so' on Ubuntu. But notice that the
builid has to match. 

If user doesn't specify the path, perf will search them internally as long
as vmlinux when recording samples. The searched debugging vdso will add to
buildid cache.

Below samples are captured on my local build kernel. perf succesfully
find debugging version vdso and we can annotate with source without
specifying vdso path.

$ sudo perf record -a
$ sudo perf report --objdump=llvm-objdump

Samples: 17K of event 'cycles:P', 4000 Hz, Event count (approx.): 1760
__vdso_clock_gettime  /work/linux-host/arch/x86/entry/vdso/vdso64.so.d
Percent│       movq    -48(%rbp),%rsi
       │       testq   %rax,%rax
       │     ;               return vread_hvclock();
       │       movq    %rax,%rdx
       │     ;               if (unlikely(!vdso_cycles_ok(cycles)))
       │     ↑ js      eb
       │     ↑ jmp     74
       │     ;               ts->tv_sec = vdso_ts->sec;
  0.02 │147:   leaq    2(%rbx),%rax
       │       shlq    $4, %rax
       │       addq    %r10,%rax
       │     ;               while ((seq = READ_ONCE(vd->seq)) & 1) {
  9.38 │152:   movl    (%r10),%ecx

When doing cross platform analysis, we need to specify the vdso path if
we are interested in its symbols. At most two vdso can be given. Also you
can pack your buildid cache with perf-archive if the debugging vdso can be
found on the sampled machine.

$ sudo perf report --objdump=llvm-objdump \
      --vdso arch/x86/entry/vdso/vdso64.so.dbg,arch/x86/entry/vdso/vdso32.so.dbg

I also improved perf-buildid-cache command recognize vdso when adding files, then
place it at correct place.

v6:
  - split "perf: build-id: try to search debugging vdso and add to cache" 
    by functional logical. (suggested by Adrian)
v5:
  - Searching the vdso in record stage instead of report. So the debugging
    vdso will be in build-id cache. This is friendly for cross-machine analysis.
  - Improve perf-buildid-cache command recognize vdso when adding files
v4:
  - split the refactoring from the actual change.
v3:
  - update documentation.
v2:
  - now search vdso automatically as long as vmlinux, as suggested by Adrian.
  - remove change 'prefer symsrc_filename for filename'.

Changbin Du (8):
  perf: support specify vdso path in cmdline
  perf: disasm: refactor function dso__disassemble_filename
  perf: disasm: use build_id_path if fallback failed
  perf: symbol: generalize vmlinux path searching
  perf: build-id: add support for build-id cache vdso debug
  perf: build-id: extend build_id_cache__find_debug() to find local
    debugging vdso
  perf: disasm: prefer debugging files in build-id cache
  perf buildid-cache: recognize vdso when adding files

 tools/perf/Documentation/perf-annotate.txt |   3 +
 tools/perf/Documentation/perf-c2c.txt      |   3 +
 tools/perf/Documentation/perf-inject.txt   |   3 +
 tools/perf/Documentation/perf-report.txt   |   3 +
 tools/perf/Documentation/perf-script.txt   |   3 +
 tools/perf/Documentation/perf-top.txt      |   3 +
 tools/perf/builtin-annotate.c              |   2 +
 tools/perf/builtin-buildid-cache.c         |  26 ++-
 tools/perf/builtin-c2c.c                   |   2 +
 tools/perf/builtin-inject.c                |   2 +
 tools/perf/builtin-report.c                |   2 +
 tools/perf/builtin-script.c                |   2 +
 tools/perf/builtin-top.c                   |   2 +
 tools/perf/util/build-id.c                 |  57 +++++-
 tools/perf/util/disasm.c                   | 131 ++++++++-----
 tools/perf/util/machine.c                  |   4 +-
 tools/perf/util/symbol.c                   | 209 ++++++++++++++++-----
 tools/perf/util/symbol.h                   |   9 +-
 tools/perf/util/symbol_conf.h              |   5 +
 19 files changed, 359 insertions(+), 112 deletions(-)

-- 
2.34.1