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]> [downstream backport] Signed-off-by: Joe Lawrence <[email protected]> --- tools/perf/util/symbol.c | 4 ++-- tools/perf/util/symbol.h | 12 ++++++++++++ 2 files changed, 14 insertions(+), 2 deletions(-) diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c index cd379ced19e5..a562702b4841 100644 --- a/tools/perf/util/symbol.c +++ b/tools/perf/util/symbol.c @@ -880,8 +880,8 @@ static int map__process_kallsym_symbol(void *arg, const char *name, if (!symbol_type__filter(type)) return 0; - /* Ignore mapping symbols in kallsyms */ - if (is_ignored_kernel_symbol(name)) + /* Ignore mapping and livepatch symbols in kallsyms */ + if (is_ignored_kernel_symbol(name) || is_livepatch_symbol(name)) return 0; /* diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h index a71525335703..d0bac824c79c 100644 --- a/tools/perf/util/symbol.h +++ b/tools/perf/util/symbol.h @@ -8,7 +8,9 @@ #include <stdint.h> #include <stdatomic.h> #include <linux/list.h> +#include <linux/livepatch_external.h> #include <linux/rbtree.h> +#include <linux/string.h> #include <stdio.h> #include <errno.h> #include "addr_location.h" @@ -45,6 +47,16 @@ static inline bool is_ignored_kernel_symbol(const char *str) return str[0] == '$'; } +/* + * Livepatch symbols (.klp.sym.*) are relocation placeholders whose resolved + * addresses alias existing kernel symbols. They carry a [module] tag which + * confuses module boundary tracking and symbol table lookups. + */ +static inline bool is_livepatch_symbol(const char *str) +{ + return strstarts(str, KLP_SYM_PREFIX); +} + /* * libelf 0.8.x and earlier do not support ELF_C_READ_MMAP; * for newer versions we can use mmap to reduce memory usage: -- 2.54.0
