[RFC PATCH v2 15/21] objtool: Don't warn about __cfi_ preambles falling through

Sami Tolvanen
2022-05-13T20:22:37Z

The __cfi_ preambles contain valid instructions, which embed KCFI
type information in the following format:

__cfi_function:
int3
int3
mov <id>, %eax
int3
int3
function:
...

While the preambles are STT_FUNC and contain valid instructions,
they are not executed and always fall through. Skip the warning for
them.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
tools/objtool/check.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index ca5b74603008..88f005ae6dcc 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3311,6 +3311,10 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
next_insn = next_insn_to_validate(file, insn);

if (func && insn->func && func != insn->func->pfunc) {
+ /* Ignore KCFI type preambles, which always fall through */
+ if (!strncmp(func->name, "__cfi_", 6))
+ return 0;
+
WARN("%s() falls through to next function %s()",
func->name, insn->func->name);
return 1;
--
2.36.0.550.gb090851708-goog