linux-kernel - [PATCH v2] arm64: ftrace: use function_nocfi for

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Message-Id: <20211005123645.2766258-1-sumit.garg@linaro.org>
Date:   Tue,  5 Oct 2021 18:06:45 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     rostedt@...dmis.org, mingo@...hat.com, catalin.marinas@....com,
        will@...nel.org, samitolvanen@...gle.com, ben.dai@...soc.com,
        mark.rutland@....com, nathan@...nel.org, keescook@...omium.org,
        ndesaulniers@...gle.com, daniel.thompson@...aro.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        Sumit Garg <sumit.garg@...aro.org>
Subject: [PATCH v2] arm64: ftrace: use function_nocfi for _mcount as well

Commit 800618f955a9 ("arm64: ftrace: use function_nocfi for ftrace_call")
only fixed address of ftrace_call but address of _mcount needs to be
fixed as well. Use function_nocfi() to get the actual address of _mcount
function as with CONFIG_CFI_CLANG, the compiler replaces function pointers
with jump table addresses which breaks dynamic ftrace as the address of
_mcount is replaced with the address of _mcount.cfi_jt.

This problem won't apply where the toolchain implements
-fpatchable-function-entry as we'll use that in preference to regular -pg,
i.e. this won't show up with recent versions of clang.

Fixes: 9186ad8e66bab6a1 ("arm64: allow CONFIG_CFI_CLANG to be selected")
Signed-off-by: Sumit Garg <sumit.garg@...aro.org>
Acked-by: Mark Rutland <mark.rutland@....com>
---

Changes in v2:
- Added fixes tag.
- Extended commit description.
- Picked up Mark's ack.

 arch/arm64/include/asm/ftrace.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index 91fa4baa1a93..347b0cc68f07 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -15,7 +15,7 @@
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
 #define ARCH_SUPPORTS_FTRACE_OPS 1
 #else
-#define MCOUNT_ADDR		((unsigned long)_mcount)
+#define MCOUNT_ADDR		((unsigned long)function_nocfi(_mcount))
 #endif
 
 /* The BL at the callsite's adjusted rec->ip */
-- 
2.17.1