kernel/arm-gcc-8-build-fixes.patch

From patchwork Fri Feb  2 15:07:34 2018
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Subject: [1/2] ARM: kvm: fix building with gcc-8
From: Arnd Bergmann <arnd@arndb.de>
X-Patchwork-Id: 10196985
Message-Id: <20180202150756.420422-1-arnd@arndb.de>
To: Christoffer Dall <christoffer.dall@linaro.org>,
 Marc Zyngier <marc.zyngier@arm.com>, Russell King <linux@armlinux.org.uk>
Cc: Nicolas Pitre <nico@linaro.org>, Andi Kleen <ak@linux.intel.com>,
 Richard Earnshaw <rearnsha@gcc.gnu.org>,
 Tamar Christina <tnfchris@gcc.gnu.org>,
 Arnd Bergmann <arnd@arndb.de>, stable@vger.kernel.org,
 Julien Thierry <julien.thierry@arm.com>,
 linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
 linux-kernel@vger.kernel.org
Date: Fri,  2 Feb 2018 16:07:34 +0100

In banked-sr.c, we use a top-level '__asm__(".arch_extension virt")'
statement to allow compilation of a multi-CPU kernel for ARMv6
and older ARMv7-A that don't normally support access to the banked
registers.

This is considered to be a programming error by the gcc developers
and will no longer work in gcc-8, where we now get a build error:

/tmp/cc4Qy7GR.s:34: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_usr'
/tmp/cc4Qy7GR.s:41: Error: Banked registers are not available with this architecture. -- `mrs r3,ELR_hyp'
/tmp/cc4Qy7GR.s:55: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_svc'
/tmp/cc4Qy7GR.s:62: Error: Banked registers are not available with this architecture. -- `mrs r3,LR_svc'
/tmp/cc4Qy7GR.s:69: Error: Banked registers are not available with this architecture. -- `mrs r3,SPSR_svc'
/tmp/cc4Qy7GR.s:76: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_abt'

Passign the '-march-armv7ve' flag to gcc works, and is ok here, because
we know the functions won't ever be called on pre-ARMv7VE machines.
Unfortunately, older compiler versions (4.8 and earlier) do not understand
that flag, so we still need to keep the asm around.

Backporting to stable kernels (4.6+) is needed to allow those to be built
with future compilers as well.

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84129
Fixes: 33280b4cd1dc ("ARM: KVM: Add banked registers save/restore")
Cc: stable@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Christoffer Dall <christoffer.dall@linaro.org>
---
 arch/arm/kvm/hyp/Makefile    | 5 +++++
 arch/arm/kvm/hyp/banked-sr.c | 4 ++++
 2 files changed, 9 insertions(+)

diff --git a/arch/arm/kvm/hyp/Makefile b/arch/arm/kvm/hyp/Makefile
index 5638ce0c9524..63d6b404d88e 100644
--- a/arch/arm/kvm/hyp/Makefile
+++ b/arch/arm/kvm/hyp/Makefile
@@ -7,6 +7,8 @@ ccflags-y += -fno-stack-protector -DDISABLE_BRANCH_PROFILING
 
 KVM=../../../../virt/kvm
 
+CFLAGS_ARMV7VE		   :=$(call cc-option, -march=armv7ve)
+
 obj-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/hyp/vgic-v2-sr.o
 obj-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/hyp/vgic-v3-sr.o
 obj-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/hyp/timer-sr.o
@@ -15,7 +17,10 @@ obj-$(CONFIG_KVM_ARM_HOST) += tlb.o
 obj-$(CONFIG_KVM_ARM_HOST) += cp15-sr.o
 obj-$(CONFIG_KVM_ARM_HOST) += vfp.o
 obj-$(CONFIG_KVM_ARM_HOST) += banked-sr.o
+CFLAGS_banked-sr.o	   += $(CFLAGS_ARMV7VE)
+
 obj-$(CONFIG_KVM_ARM_HOST) += entry.o
 obj-$(CONFIG_KVM_ARM_HOST) += hyp-entry.o
 obj-$(CONFIG_KVM_ARM_HOST) += switch.o
+CFLAGS_switch.o		   += $(CFLAGS_ARMV7VE)
 obj-$(CONFIG_KVM_ARM_HOST) += s2-setup.o
diff --git a/arch/arm/kvm/hyp/banked-sr.c b/arch/arm/kvm/hyp/banked-sr.c
index 111bda8cdebd..be4b8b0a40ad 100644
--- a/arch/arm/kvm/hyp/banked-sr.c
+++ b/arch/arm/kvm/hyp/banked-sr.c
@@ -20,6 +20,10 @@
 
 #include <asm/kvm_hyp.h>
 
+/*
+ * gcc before 4.9 doesn't understand -march=armv7ve, so we have to
+ * trick the assembler.
+ */
 __asm__(".arch_extension     virt");
 
 void __hyp_text __banked_save_state(struct kvm_cpu_context *ctxt)
From patchwork Fri Feb  2 15:07:35 2018
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Subject: [2/2] ARM: xscale: fix gcc-8 build
From: Arnd Bergmann <arnd@arndb.de>
X-Patchwork-Id: 10196991
Message-Id: <20180202150756.420422-2-arnd@arndb.de>
To: Russell King <linux@armlinux.org.uk>
Cc: Nicolas Pitre <nico@linaro.org>, Andi Kleen <ak@linux.intel.com>,
 Richard Earnshaw <rearnsha@gcc.gnu.org>,
 Tamar Christina <tnfchris@gcc.gnu.org>, Arnd Bergmann <arnd@arndb.de>,
 linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Date: Fri,  2 Feb 2018 16:07:35 +0100

We use a hack in xscale-cp0.c to allow building it for ARMv4 while
also using ARMv5TE and iWMMXt specific inline assembly, by
adding a top-level asm statement.

Unfortunately that hack no longer works with gcc-8, since it will
revert back to the normal architecture. The recommended way of
handling this is to use __attribute__((target("armv5te"))) on the
functions that need it, or #pragma GCC target("arch=armv5te").
Either of those work with gcc-8, but not earlier versions, and
it seems worse to combine that with the old hack.

Instead, this adds the .arch statement to each inline assembler
statement that needs it individually. That is also slightly uglier
than the previous hack, but it works with all compiler versions
and documents better why we need the override in the first place.

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84129
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Nicolas Pitre <nico@linaro.org>
---
 arch/arm/kernel/xscale-cp0.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/arm/kernel/xscale-cp0.c b/arch/arm/kernel/xscale-cp0.c
index 77a2eef72115..e06a2f6dac4f 100644
--- a/arch/arm/kernel/xscale-cp0.c
+++ b/arch/arm/kernel/xscale-cp0.c
@@ -17,11 +17,10 @@
 #include <asm/thread_notify.h>
 #include <asm/cputype.h>
 
-asm("	.arch armv5te\n");
-
 static inline void dsp_save_state(u32 *state)
 {
 	__asm__ __volatile__ (
+		".arch	armv5te\n\t"
 		"mrrc	p0, 0, %0, %1, c0\n"
 		: "=r" (state[0]), "=r" (state[1]));
 }
@@ -29,6 +28,7 @@ static inline void dsp_save_state(u32 *state)
 static inline void dsp_load_state(u32 *state)
 {
 	__asm__ __volatile__ (
+		".arch	armv5te\n\t"
 		"mcrr	p0, 0, %0, %1, c0\n"
 		: : "r" (state[0]), "r" (state[1]));
 }
@@ -134,7 +134,8 @@ static int __init cpu_has_iwmmxt(void)
 	 *	tmrrc	%0, %1, wR0
 	 */
 	__asm__ __volatile__ (
-		"mcrr	p0, 0, %2, %3, c0\n"
+		".arch	armv5te\n\t"
+		"mcrr	p0, 0, %2, %3, c0\n\t"
 		"mrrc	p0, 0, %0, %1, c0\n"
 		: "=r" (lo), "=r" (hi)
 		: "r" (0), "r" (0x100));