[UNIKRAFT PATCH 2/2] arch/arm: Provide ukarch_spinwait noop for ARM

[Alexander Jung <a.jung@xxxxxxxxxxx>]

ARM does not support a pause-type instruction for busy spin wait
operations.  This commit provides the same alias to be used in
instances where it is required but defaults to a blank operation.

Signed-off-by: Alexander Jung <alexander.jung@xxxxxxxxx>
---
 arch/arm/arm/include/uk/asm/lcpu.h   | 5 +++++
 arch/arm/arm64/include/uk/asm/lcpu.h | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/arch/arm/arm/include/uk/asm/lcpu.h 
b/arch/arm/arm/include/uk/asm/lcpu.h
index cdeffc3..f38ffb9 100644
--- a/arch/arm/arm/include/uk/asm/lcpu.h
+++ b/arch/arm/arm/include/uk/asm/lcpu.h
@@ -57,3 +57,8 @@ struct __regs {
 #ifndef wmb
 #define wmb() __asm__("dsb" : : : "memory")
 #endif
+
+static inline void ukarch_spinwait(void)
+{
+       /* Intelligent busy wait not supported on arm. */
+}
diff --git a/arch/arm/arm64/include/uk/asm/lcpu.h 
b/arch/arm/arm64/include/uk/asm/lcpu.h
index 45d1b23..51e17ad 100644
--- a/arch/arm/arm64/include/uk/asm/lcpu.h
+++ b/arch/arm/arm64/include/uk/asm/lcpu.h
@@ -146,4 +146,9 @@ static inline unsigned long ukarch_read_sp(void)
        return sp;
 }
 
+static inline void ukarch_spinwait(void)
+{
+       /* Intelligent busy wait not supported on arm64. */
+}
+
 #endif /* __ASSEMBLY__ */
-- 
2.11.0