From: Nathan Chancellor <natechancellor@gmail.com>
To: Russell King <linux@armlinux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>,
Matthias Kaehlcke <mka@chromium.org>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com,
Nathan Chancellor <natechancellor@gmail.com>,
Nick Desaulniers <ndesaulniers@google.com>,
Stefan Agner <stefan@agner.ch>
Subject: [PATCH v2] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer
Date: Fri, 30 Aug 2019 23:05:31 -0700 [thread overview]
Message-ID: <20190831060530.43082-1-natechancellor@gmail.com> (raw)
In-Reply-To: <20190829062635.45609-1-natechancellor@gmail.com>
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: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
v1 -> v2:
* Add Nick and Stefan's reviewed by tags
* Move version check from Makefile to Kconfig. This prevents '-pg` from
ever being added if '-meabi gnu' would produce a non-booting kernel
and it allows clang 9.0.0 and earlier to build and link all*config
kernels because the function tracer can't be selected.
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 a98c7af50bf0..440ad41e77e4 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -83,7 +83,7 @@ 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 a43fc753aa53..aa7023db66c7 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -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)
--
2.23.0
next prev parent reply other threads:[~2019-08-31 6:08 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-29 6:26 [PATCH] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer Nathan Chancellor
2019-08-29 7:57 ` Stefan Agner
2019-08-29 16:20 ` Matthias Kaehlcke
2019-08-29 17:55 ` Nick Desaulniers
2019-08-29 19:34 ` Nathan Chancellor
2019-08-29 20:21 ` Stefan Agner
2019-08-29 20:57 ` Nick Desaulniers
2019-08-30 17:28 ` Nathan Chancellor
2019-08-30 21:13 ` Nick Desaulniers
2019-08-30 21:15 ` Nick Desaulniers
2019-08-31 6:05 ` Nathan Chancellor [this message]
2019-09-03 18:48 ` [PATCH v2] " Matthias Kaehlcke
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