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Subject[PATCH v7 05/25] arm64: Build vDSO with -ffixed-x18
From: Peter Collingbourne <>

The vDSO needs to be build with x18 reserved in order to accommodate
userspace platform ABIs built on top of Linux that use the register
to carry inter-procedural state, as provided for by the AAPCS.
An example of such a platform ABI is the one that will be used by an
upcoming version of Android.

Although this change is currently a no-op due to the fact that the vDSO
is currently implemented in pure assembly on arm64, it is necessary
in order to prepare for another change [1] that will add C code to
the vDSO.


Signed-off-by: Peter Collingbourne <>
Signed-off-by: Vincenzo Frascino <>
Tested-by: Shijith Thotton <>
Tested-by: Andre Przywara <>
Cc: Mark Salyzyn <>
Cc: Will Deacon <>
arch/arm64/kernel/vdso/Makefile | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
index 3acfc813e966..ec81d28aeb5d 100644
--- a/arch/arm64/kernel/vdso/Makefile
+++ b/arch/arm64/kernel/vdso/Makefile
@@ -20,7 +20,7 @@ obj-vdso := $(addprefix $(obj)/, $(obj-vdso))
ldflags-y := -shared -nostdlib --hash-style=sysv \
--build-id -n -T

-ccflags-y := -fno-common -fno-builtin -fno-stack-protector
+ccflags-y := -fno-common -fno-builtin -fno-stack-protector -ffixed-x18

VDSO_LDFLAGS := -Bsymbolic
 \ /
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