linux-kernel - [PATCH v7 05/25] arm64: Build vDSO with -ffixed-x18

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Message-Id: <20190621095252.32307-6-vincenzo.frascino@arm.com>
Date:   Fri, 21 Jun 2019 10:52:32 +0100
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Russell King <linux@...linux.org.uk>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Shuah Khan <shuah@...nel.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Huw Davies <huw@...eweavers.com>,
        Shijith Thotton <sthotton@...vell.com>,
        Andre Przywara <andre.przywara@....com>,
        Mark Salyzyn <salyzyn@...gle.com>
Subject: [PATCH v7 05/25] arm64: Build vDSO with -ffixed-x18

From: Peter Collingbourne <pcc@...gle.com>

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.

[1] https://patchwork.kernel.org/patch/10044501/

Signed-off-by: Peter Collingbourne <pcc@...gle.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
Tested-by: Shijith Thotton <sthotton@...vell.com>
Tested-by: Andre Przywara <andre.przywara@....com>
Cc: Mark Salyzyn <salyzyn@...gle.com>
Cc: Will Deacon <will.deacon@....com>
Cc: linux-arm-kernel@...ts.infradead.org
---
 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 -soname=linux-vdso.so.1 --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
 ccflags-y += -DDISABLE_BRANCH_PROFILING
 
 VDSO_LDFLAGS := -Bsymbolic
-- 
2.21.0