[PATCH] x86/ftrace: Mark ftrace_modify_code_direct() __ref

[Borislav Petkov]

On Sat, Nov 16, 2019 at 09:46:07PM +0100, Borislav Petkov wrote:
> WARNING: vmlinux.o(.text+0x8c0b1): Section mismatch in reference from the function ftrace_modify_code_direct() to the function .init.text:text_poke_early()
> The function ftrace_modify_code_direct() references
> the function __init text_poke_early().
> This is often because ftrace_modify_code_direct lacks a __init 
> annotation or the annotation of text_poke_early is wrong.
> 
> FATAL: modpost: Section mismatches detected.
> Set CONFIG_SECTION_MISMATCH_WARN_ONLY=y to allow them.
> make[1]: *** [scripts/Makefile.modpost:66: __modpost] Error 1
> make: *** [Makefile:1077: vmlinux] Error 2

Here's a fix suggested by Peter:

---
From: Borislav Petkov <bp@xxxxxxx>
Subject: [PATCH] x86/ftrace: Mark ftrace_modify_code_direct() __ref

... because it calls the .init.text function text_poke_early(). That is
ok because it does call that function early, during boot.

Fixes: 9706f7c3531f ("x86/ftrace: Use text_poke()")
Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20191116204607.GC23231@xxxxxxx
---
 arch/x86/kernel/ftrace.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 2a179fb35cd1..108ee96f8b66 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -99,7 +99,12 @@ static int ftrace_verify_code(unsigned long ip, const char *old_code)
 	return 0;
 }
 
-static int
+/*
+ * Marked __ref because it calls text_poke_early() which is .init.text. That is
+ * ok because that call will happen early, during boot, when .init sections are
+ * still present.
+ */
+static int __ref
 ftrace_modify_code_direct(unsigned long ip, const char *old_code,
 			  const char *new_code)
 {
-- 
2.21.0

-- 
Regards/Gruss,
    Boris.

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