[PATCH -rcu/kcsan 23/23] objtool, kcsan: Remove memory barrier instrumentation from noinstr

Marco Elver
2021-10-05T11:02:20Z

Teach objtool to turn instrumentation required for memory barrier
modeling into nops in noinstr text.

The __tsan_func_entry/exit calls are still emitted by compilers even
with the __no_sanitize_thread attribute. The memory barrier
instrumentation will be inserted explicitly (without compiler help), and
thus needs to also explicitly be removed.

Signed-off-by: Marco Elver <elver@google.com>
---
tools/objtool/check.c | 32 ++++++++++++++++++++++++++------
1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 7e8cd3ba5482..7b694e639164 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -965,6 +965,31 @@ static struct symbol *find_call_destination(struct section *sec, unsigned long o
return call_dest;
}

+static bool should_remove_if_noinstr(const char *name)
+{
+ /*
+ * Many compilers cannot disable KCOV with a function attribute so they
+ * need a little help, NOP out any KCOV calls from noinstr text.
+ */
+ if (!strncmp(name, "__sanitizer_cov_", 16))
+ return true;
+
+ /*
+ * Compilers currently do not remove __tsan_func_entry/exit with the
+ * __no_sanitize_thread attribute, remove them. Memory barrier
+ * instrumentation is not emitted by the compiler, but inserted
+ * explicitly, so we need to also remove them.
+ */
+ if (!strncmp(name, "__tsan_func_", 12) ||
+ !strcmp(name, "__kcsan_mb") ||
+ !strcmp(name, "__kcsan_wmb") ||
+ !strcmp(name, "__kcsan_rmb") ||
+ !strcmp(name, "__kcsan_release"))
+ return true;
+
+ return false;
+}
+
/*
* Find the destination instructions for all calls.
*/
@@ -1031,13 +1056,8 @@ static int add_call_destinations(struct objtool_file *file)
&file->static_call_list);
}

- /*
- * Many compilers cannot disable KCOV with a function attribute
- * so they need a little help, NOP out any KCOV calls from noinstr
- * text.
- */
if (insn->sec->noinstr &&
- !strncmp(insn->call_dest->name, "__sanitizer_cov_", 16)) {
+ should_remove_if_noinstr(insn->call_dest->name)) {
if (reloc) {
reloc->type = R_NONE;
elf_write_reloc(file->elf, reloc);
--
2.33.0.800.g4c38ced690-goog