Re: [PATCH] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer
From: Stefan Agner <stefan@agner.ch>
Date: 2019-08-29 07:57:13
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On 2019-08-29 08:26, Nathan Chancellor wrote:
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 because the calling convention was not correct. Now that it is fixed, add this to the command line when clang is 10.0.0 or newer so everything works properly.
Cool, finally function tracing with Clang :-)
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 Signed-off-by: Nathan Chancellor <redacted>
Reviewed-by: Stefan Agner <stefan@agner.ch> -- Stefan
quoted hunk ↗ jump to hunk
--- arch/arm/Makefile | 6 ++++++ 1 file changed, 6 insertions(+)diff --git a/arch/arm/Makefile b/arch/arm/Makefile index c3624ca6c0bc..7b5a26a866fc 100644 --- a/arch/arm/Makefile +++ b/arch/arm/Makefile@@ -112,6 +112,12 @@ ifeq ($(CONFIG_ARM_UNWIND),y) CFLAGS_ABI +=-funwind-tables endif +ifeq ($(CONFIG_CC_IS_CLANG),y) +ifeq ($(shell test $(CONFIG_CLANG_VERSION) -ge 100000; echo $$?),0) +CFLAGS_ABI +=-meabi gnu +endif +endif + # Accept old syntax despite ".syntax unified" AFLAGS_NOWARN :=$(call as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W)
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