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Date:   Thu,  3 Mar 2022 17:06:42 +0800
From:   David Gow <>
To:     Kees Cook <>
Cc:     David Gow <>, Jeff Dike <>,
        Richard Weinberger <>,
        Anton Ivanov <>,
        Masahiro Yamada <>,
        Nick Desaulniers <>,
        Nathan Chancellor <>,,,,,,,
Subject: [PATCH] um: clang: Strip out -mno-global-merge from USER_CFLAGS

The things built with USER_CFLAGS don't seem to recognise it as a
compiler option, and print a warning:
clang: warning: argument unused during compilation: '-mno-global-merge' [-Wunused-command-line-argument]

Fixes: 744814d2fa ("um: Allow builds with Clang")
Signed-off-by: David Gow <>

This warning shows up after merging:

I'm not 100% sure why this is necessary, but it does seem to work. All
the attempts to get rid of -mno-global-merge entirely have been met with
skepticism, but I'm guessing that it's not a problem for just the UML
"user" files, as they shouldn't(?) interact too much with modules.

 arch/um/Makefile | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/um/Makefile b/arch/um/Makefile
index f2fe63bfd819..320b09cd513c 100644
--- a/arch/um/Makefile
+++ b/arch/um/Makefile
@@ -75,6 +75,10 @@ USER_CFLAGS = $(patsubst $(KERNEL_DEFINES),,$(patsubst -I%,,$(KBUILD_CFLAGS))) \
 		-D_FILE_OFFSET_BITS=64 -idirafter $(srctree)/include \
 		-idirafter $(objtree)/include -D__KERNEL__ -D__UM_HOST__
+USER_CFLAGS := $(patsubst -mno-global-merge,,$(USER_CFLAGS))
 #This will adjust *FLAGS accordingly to the platform.
 include $(srctree)/$(ARCH_DIR)/Makefile-os-$(OS)

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