[PATCH 5.3 111/166] ARM: 8905/1: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer

Greg Kroah-Hartman
2019-10-06T17:43:56Z

From: Nathan Chancellor <natechancellor@gmail.com>

[ Upstream commit b0fe66cf095016e0b238374c10ae366e1f087d11 ]

Currently, multi_v7_defconfig + CONFIG_FUNCTION_TRACER fails to build
with clang:

arm-linux-gnueabi-ld: kernel/softirq.o: in function `_local_bh_enable':
softirq.c:(.text+0x504): undefined reference to `mcount'
arm-linux-gnueabi-ld: kernel/softirq.o: in function `__local_bh_enable_ip':
softirq.c:(.text+0x58c): undefined reference to `mcount'
arm-linux-gnueabi-ld: kernel/softirq.o: in function `do_softirq':
softirq.c:(.text+0x6c8): undefined reference to `mcount'
arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_enter':
softirq.c:(.text+0x75c): undefined reference to `mcount'
arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_exit':
softirq.c:(.text+0x840): undefined reference to `mcount'
arm-linux-gnueabi-ld: kernel/softirq.o:softirq.c:(.text+0xa50): more undefined references to `mcount' follow

clang can emit a working mcount symbol, __gnu_mcount_nc, when
'-meabi gnu' is passed to it. Until r369147 in LLVM, this was
broken and caused the kernel not to boot with '-pg' because the
calling convention was not correct. Always build with '-meabi gnu'
when using clang but ensure that '-pg' (which is added with
CONFIG_FUNCTION_TRACER and its prereq CONFIG_HAVE_FUNCTION_TRACER)
cannot be added with it unless this is fixed (which means using
clang 10.0.0 and newer).

Link: https://github.com/ClangBuiltLinux/linux/issues/35
Link: https://bugs.llvm.org/show_bug.cgi?id=33845
Link: https://github.com/llvm/llvm-project/commit/16fa8b09702378bacfa3d07081afe6b353b99e60

Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/arm/Kconfig | 2 +-
arch/arm/Makefile | 4 ++++
2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 5e2c68e9dd6e2..b587a3b3939ab 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -82,7 +82,7 @@ config ARM
select HAVE_FAST_GUP if ARM_LPAE
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_GCC || CLANG_VERSION >= 100000)
select HAVE_GCC_PLUGINS
select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7)
select HAVE_IDE if PCI || ISA || PCMCIA
diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index c3624ca6c0bca..9b3d4deca9e4e 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -112,6 +112,10 @@ ifeq ($(CONFIG_ARM_UNWIND),y)
CFLAGS_ABI +=-funwind-tables
endif

+ifeq ($(CONFIG_CC_IS_CLANG),y)
+CFLAGS_ABI += -meabi gnu
+endif
+
# Accept old syntax despite ".syntax unified"
AFLAGS_NOWARN :=$(call as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W)

--
2.20.1