[PATCH v2 0/2] perf symbols: skip livepatch symbols

[Joe Lawrence <joe.lawrence@redhat.com>]

This patchset fixes two minor perf bugs when livepatches containing
special so-called livepatch symbols are loaded.  In both cases, perf
should ignore these symbols as they resolve as relocations to kernel
addresses and not module space.

- Patch 1 fixes `perf test 1`
- Patch 2 fixes `perf record --kcore` bloat


Testing notes
=============

("perf symbols: skip livepatch symbols when loading kallsyms"):

  Without patch:
  ./tools/perf/perf test 1
    1: vmlinux symtab matches kallsyms                     : FAILED!

  With patch:
  ./tools/perf/perf test 1
    1: vmlinux symtab matches kallsyms                     : Ok

("perf symbols: skip livepatch symbols in kcore_copy")

  1. Baseline = pre-patch perf, no livepatch
  ------------------------------------------
  
  $ ./tools/perf/perf record --kcore -a -o /tmp/baseline.data -- sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.221 MB /tmp/baseline.data (1717 samples) ]
  
  $ tree --noreport -h /tmp/baseline.data
  /tmp/baseline.data
  |-- [ 235K]  data
  `-- [   50]  kcore_dir
      |-- [  11M]  kallsyms
      |-- [  25M]  kcore
      `-- [ 1.7K]  modules
  
  
  2. Bloated kcore = pre-patch perf, with livepatch
  -------------------------------------------------
  
  $ insmod kpatch-5_14_0-570_94_1-1-3.ko
  $ ./tools/perf/perf record --kcore -a -o /tmp/klp-bloated.data -- sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.274 MB /tmp/klp-bloated.data (2757 samples) ]
  
  $ tree --noreport  -h /tmp/klp-bloated.data
  /tmp/klp-bloated.data
  |-- [ 288K]  data
  `-- [   50]  kcore_dir
      |-- [  11M]  kallsyms
      |-- [  68M]  kcore
      `-- [ 1.8K]  modules
  
  
  3. Post-fix = patched perf, with livepatch
  ------------------------------------------
  
  [ kpatch-5_14_0-570_94_1-1-3.ko still loaded from test (2) ]
  
  $ ./tools/perf/perf record --kcore -a -o /tmp/postfix.data -- sleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.274 MB /tmp/postfix.data (2763 samples) ]
  
  $ tree --noreport -h /tmp/postfix.data
  /tmp/postfix.data
  |-- [ 289K]  data
  `-- [   50]  kcore_dir
      |-- [  11M]  kallsyms
      |-- [  25M]  kcore
      `-- [ 1.8K]  modules

Changes
=======

v2:
- Move klp symbol check into tools/perf/util/symbol.h alongside similar
  is_ignored_kernel_symbol() check [Petr]
- Use KLP_SYM_PREFIX instead of inlining it [Petr]
- Add similar check to kcore_copy__process_kallsyms() [Sashiko]

- Note: Sashiko flagged a pre-existing off-by-one in kallsyms__parse()
  where the symbol-name loop could write past symbol_name[] on overlong
  entries. That issue is unrelated to livepatch symbols and was already
  fixed by Rui Qi's 68018df3f55e ("perf: Fix off-by-one stack buffer
  overflow in kallsyms__parse()").

v1: https://lore.kernel.org/linux-perf-users/ajzwjNncrI3Bob_o@pathway.suse.cz/T/#t

Joe Lawrence (2):
  perf symbols: skip livepatch symbols when loading kallsyms
  perf symbols: skip livepatch symbols in kcore_copy kallsyms processing

 tools/perf/util/symbol-elf.c |  4 ++++
 tools/perf/util/symbol.c     |  4 ++--
 tools/perf/util/symbol.h     | 12 ++++++++++++
 3 files changed, 18 insertions(+), 2 deletions(-)

-- 
2.54.0