LKML Archive on
 help / color / Atom feed
From: Nathan Chancellor <>
To: Russell King <>
Cc: Nick Desaulniers <>,
	Arnd Bergmann <>, Stefan Agner <>,
	Matthias Kaehlcke <>,,,,
	Nathan Chancellor <>
Subject: [PATCH] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer
Date: Wed, 28 Aug 2019 23:26:35 -0700
Message-ID: <> (raw)

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.

Signed-off-by: Nathan Chancellor <>
 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 ($(CONFIG_ARM_UNWIND),y)
 CFLAGS_ABI	+=-funwind-tables
+ifeq ($(CONFIG_CC_IS_CLANG),y)
+ifeq ($(shell test $(CONFIG_CLANG_VERSION) -ge 100000; echo $$?),0)
+CFLAGS_ABI	+=-meabi gnu
 # Accept old syntax despite ".syntax unified"
 AFLAGS_NOWARN	:=$(call as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W)

             reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-29  6:26 Nathan Chancellor [this message]
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 ` [PATCH v2] " Nathan Chancellor
2019-09-03 18:48   ` Matthias Kaehlcke

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on

Archives are clonable:
	git clone --mirror lkml/git/0.git
	git clone --mirror lkml/git/1.git
	git clone --mirror lkml/git/2.git
	git clone --mirror lkml/git/3.git
	git clone --mirror lkml/git/4.git
	git clone --mirror lkml/git/5.git
	git clone --mirror lkml/git/6.git
	git clone --mirror lkml/git/7.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ \
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone