Hello,
On Fri, Jun 26, 2026 at 05:21:38PM -0400, Joe Lawrence wrote:
> 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()").
Petr, are you ok with this change?
Thanks,
Namhyung
>
> v1:
> https://lore.kernel.org/linux-perf-users/[email protected]/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
>
