[PATCH] perf symbols: ignore livepatch symbols

[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>
Signed-off-by: Joe Lawrence <joe.lawrence@xxxxxxxxxx>
---
 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