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BACKPORT: ARM: 8905/1: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer

Browse source 
commit b0fe66cf095016e0b238374c10ae366e1f087d11 upstream.

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: 16fa8b0970

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>

Bug: 145525910
[nd: Kconfig change differs due to missing f00790aaf2e2]
Change-Id: I280bd7c0422c68284ed31e2134ccef8997832737
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
This commit is contained in:
Nathan Chancellor 2019-12-04 14:50:28 -08:00 • committed by Nick Desaulniers
commit 4bd3f510b9
2 changed files with 5 additions and 1 deletions
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2
arch/arm/Kconfig
View file

@ -69,7 +69,7 @@ config ARM
select HAVE_EXIT_THREAD
select HAVE_FTRACE_MCOUNT_RECORD if (!XIP_KERNEL)
select HAVE_FUNCTION_GRAPH_TRACER if (!THUMB2_KERNEL)
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_GENERIC_DMA_COHERENT
select HAVE_HW_BREAKPOINT if (PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7))

4
arch/arm/Makefile
View file

@ -115,6 +115,10 @@ 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)