[PATCH v2 0/4] perf: support specify vdso path in cmdline

Changbin Du
2024-06-15T09:20:35Z

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

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.

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

v2:
- now search vdso automatically as long as vmlinux, as suggested by Adrian.
- remove change 'prefer symsrc_filename for filename'.

Changbin Du (4):
perf: support specify vdso path in cmdline
perf: disasm: use build_id_path if fallback failed
perf: symbol: generalize vmlinux path searching
perf: symbol: try to seach vdso path if not given by user

tools/perf/builtin-annotate.c | 3 +
tools/perf/builtin-c2c.c | 2 +
tools/perf/builtin-inject.c | 2 +
tools/perf/builtin-kallsyms.c | 2 +
tools/perf/builtin-probe.c | 2 +
tools/perf/builtin-report.c | 2 +
tools/perf/builtin-script.c | 2 +
tools/perf/builtin-top.c | 4 +
tools/perf/tests/builtin-test.c | 3 +-
tools/perf/util/disasm.c | 122 ++++++++++-------
tools/perf/util/machine.c | 4 +-
tools/perf/util/symbol.c | 232 +++++++++++++++++++++++++-------
tools/perf/util/symbol.h | 9 +-
tools/perf/util/symbol_conf.h | 6 +
14 files changed, 293 insertions(+), 102 deletions(-)

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2.34.1