[RFC PATCH v3 15/20] objtool: Disable CFI warnings

Sami Tolvanen
2022-06-10T23:35:52Z

The __cfi_ preambles contain int3 padding and a mov instruction that
embeds the KCFI type identifier in the following format:

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

While the preamble symbols are STT_FUNC and contain valid
instructions, they are never executed and always fall through. Skip
the warning for them.

.kcfi_traps sections point to CFI traps in text sections. Also skip
the warning about them referencing !ENDBR instructions.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
tools/objtool/check.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 864bb9dd3584..337b92c3b755 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3207,6 +3207,10 @@ 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;
@@ -3827,7 +3831,8 @@ static int validate_ibt(struct objtool_file *file)
!strcmp(sec->name, "__ex_table") ||
!strcmp(sec->name, "__jump_table") ||
!strcmp(sec->name, "__mcount_loc") ||
- !strcmp(sec->name, "__tracepoints"))
+ !strcmp(sec->name, "__tracepoints") ||
+ !strcmp(sec->name, ".kcfi_traps"))
continue;

list_for_each_entry(reloc, &sec->reloc->reloc_list, list)
--
2.36.1.476.g0c4daa206d-goog