[PATCH v2 1/2] perf symbols: skip livepatch symbols when loading kallsyms

[Joe Lawrence]

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 <bprockno@xxxxxxxxxx> [downstream backport]
Signed-off-by: Joe Lawrence <joe.lawrence@xxxxxxxxxx>
---
 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