On Wed 2026-06-24 16:12:54, Joe Lawrence wrote: > Livepatch modules contain special symbols (prefixed by ".klp.sym.") that > act as relocation placeholders. Once resolved, they point to the same > addresses as the original kernel symbols they reference. [1] > > These special symbols confuse the 'vmlinux symtab matches kallsyms' perf > test as kallsyms may report multiple symbols sharing a single kernel > address. For example: > > kallsyms (without livepatch) > ---------------------------- > ffffffff81a41110 T __pfx_arch_release_task_struct > > ffffffff81a41120 T arch_release_task_struct > ffffffff81a41140 T __pfx_exit_thread > ffffffff81a41150 T exit_thread > > kallsyms (with livepatch loaded) > --------------------------------- > ffffffff81a41110 T __pfx_arch_release_task_struct > > ffffffff81a41120 T arch_release_task_struct > ffffffff81a41140 T __pfx_exit_thread > ffffffff81a41150 T exit_thread > > ffffffff81a41120 w .klp.sym.vmlinux.arch_release_task_struct,0 > > [kpatch_5_14_0_570_94_1_1_3] > > When perf loads kallsyms, both symbols are inserted into the > symbol table at the same address, corrupting symbol end-address > calculations and causing test failures. > > Filter out symbols prefixed with ".klp.sym." when loading kallsyms, as > they alias existing kernel symbols. > > Link: > https://docs.kernel.org/livepatch/module-elf-format.html#livepatch-symbols [1] > Reported-and-tested-by: Ben Procknow <[email protected]> > Signed-off-by: Joe Lawrence <[email protected]> > --- > tools/perf/util/symbol.c | 4 ++++ > 1 file changed, 4 insertions(+) > > >From Ben's tests: > > 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 > > diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c > index fcaeeddbbb6b..eeaed3f5cf50 100644 > --- a/tools/perf/util/symbol.c > +++ b/tools/perf/util/symbol.c > @@ -774,6 +774,10 @@ static int map__process_kallsym_symbol(void *arg, const > char *name, > if (name[0] == '$') > return 0;
It seems that the above checks has been moved into is_ignored_kernel_symbol(), in the current Linus' tree, see https://lore.kernel.org/lkml/[email protected]/ > + /* Ignore livepatch symbols */ > + if (strstarts(name, ".klp.sym.")) > + return 0; I guess that this check should be moved there as well. Nit: It might be possible to include <linux/livepatch_external.h> and use KLP_SYM_PREFIX instead of ".klp.sym." > + > /* > * module symbols are not sorted so we add all > * symbols, setting length to 0, and rely on Best Regards, Petr
