[PATCH v2 4/9] compiler_types: Let notrace keep the function prefix NOPs

["Jose Fernandez (Anthropic)" <jose.fernandez@linux.dev>]

Let notrace keep the prefix NOPs when the architecture defines
CC_USING_PATCHABLE_FUNCTION_PREFIX. kCFI callers check the type hash
at a fixed offset before the entry point, so a notrace function needs
the same prefix NOPs as any other. Record the entry in a section the
linker drops, so ftrace never sees it. Clang 21 takes a section name
as a third argument of the attribute. Nothing defines the macro yet,
so no functional change.

Reviewed-by: Ben Cressey <ben@cressey.dev>
Reviewed-by: Florent Revest (Anthropic) <florent.revest@linux.dev>
Assisted-by: LLM
Signed-off-by: Jose Fernandez (Anthropic) <jose.fernandez@linux.dev>
---
 include/linux/compiler_types.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index c5921f1390079..43dafaa061942 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -211,6 +211,15 @@ struct ftrace_likely_data {
 
 #if defined(CC_USING_HOTPATCH)
 #define notrace			__attribute__((hotpatch(0, 0)))
+#elif defined(CC_USING_PATCHABLE_FUNCTION_PREFIX) && !defined(__BINDGEN__)
+/*
+ * Not for bindgen: its libclang may not support the section argument
+ * (Clang >= 21), and leaving the attribute out does not change the ABI.
+ */
+#define notrace								\
+	__attribute__((patchable_function_entry(CC_USING_PATCHABLE_FUNCTION_PREFIX, \
+						 CC_USING_PATCHABLE_FUNCTION_PREFIX, \
+						 ".discard.patchable_function_entries")))
 #elif defined(CC_USING_PATCHABLE_FUNCTION_ENTRY)
 #define notrace			__attribute__((patchable_function_entry(0, 0)))
 #else

-- 
2.52.0