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; + /* Ignore livepatch symbols */ + if (strstarts(name, ".klp.sym.")) + return 0; + /* * module symbols are not sorted so we add all * symbols, setting length to 0, and rely on -- 2.54.0
