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From:   Tri Vo <trong@android.com>
To:     linux@armlinux.org.uk, yamada.masahiro@socionext.com
Cc:     ndesaulniers@google.com, stefan@agner.ch,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        Tri Vo <trong@android.com>
Subject: [PATCH] ARM: disable FUNCTION_TRACER when building with Clang
Date:   Wed, 22 May 2019 17:56:57 -0700
Message-Id: <20190523005657.170008-1-trong@android.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Clang needs "-meabi gnu" flag to emit calls to "__gnu_mcount_nc".
Otherwise, it inserts calls to undefined "mcount".

  kernel/softirq.o: In function `_local_bh_enable':
  ...
  undefined reference to `mcount'

"-meabi gnu" resolves link failures.  However, Clang does not implement
calls to "__gnu_mcount_nc" correctly.  It does not save the link
register on the stack, which corrupts the stack.  The resulting kernel
does not boot.

Disable FUNCTION_TRACER support when building with Clang.

Link: https://github.com/ClangBuiltLinux/linux/issues/35
Suggested-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Tri Vo <trong@android.com>
---
 arch/arm/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 8869742a85df..7a1804392795 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -75,7 +75,7 @@ config ARM
 	select HAVE_EXIT_THREAD
 	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
 	select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL && !CC_IS_CLANG
-	select HAVE_FUNCTION_TRACER if !XIP_KERNEL
+	select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !CC_IS_CLANG
 	select HAVE_GCC_PLUGINS
 	select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7)
 	select HAVE_IDE if PCI || ISA || PCMCIA
-- 
2.21.0.1020.gf2820cf01a-goog