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

[Marco Elver]

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@xxxxxxxxxx>
---
 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