[Xen-devel] [PATCH] xen: arm: correct use of find_next_bit

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

find_next_bit takes a "const unsigned long *" but forcing a cast of an
"uint32_t *" throws away the alignment constraints and ends up causing an
alignment fault on arm64 if the input happened to be 4 but not 8 byte aligned.

Instead of casting use a temporary variable of the right type.

I've had a look around for similar constructs and the only thing I found was
maintenance_interrupt which cases a uint64_t down to an unsigned long, which
although perhaps not best advised is safe I think.

This was observed with the AArch64 Linaro toolchain 2013.12 but I think that
is just coincidental due to subtle changes to the stack layout etc.

Reported-by: Fu Wei <fu.wei@xxxxxxxxxx>
Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 xen/arch/arm/vgic.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/vgic.c b/xen/arch/arm/vgic.c
index 90e9707..553411d 100644
--- a/xen/arch/arm/vgic.c
+++ b/xen/arch/arm/vgic.c
@@ -362,11 +362,12 @@ read_as_zero:
 
 static void vgic_disable_irqs(struct vcpu *v, uint32_t r, int n)
 {
+    const unsigned long mask = r;
     struct pending_irq *p;
     unsigned int irq;
     int i = 0;
 
-    while ( (i = find_next_bit((const long unsigned int *) &r, 32, i)) < 32 ) {
+    while ( (i = find_next_bit(&mask, 32, i)) < 32 ) {
         irq = i + (32 * n);
         p = irq_to_pending(v, irq);
         clear_bit(GIC_IRQ_GUEST_ENABLED, &p->status);
@@ -379,11 +380,12 @@ static void vgic_disable_irqs(struct vcpu *v, uint32_t r, 
int n)
 
 static void vgic_enable_irqs(struct vcpu *v, uint32_t r, int n)
 {
+    const unsigned long mask = r;
     struct pending_irq *p;
     unsigned int irq;
     int i = 0;
 
-    while ( (i = find_next_bit((const long unsigned int *) &r, 32, i)) < 32 ) {
+    while ( (i = find_next_bit(&mask, 32, i)) < 32 ) {
         irq = i + (32 * n);
         p = irq_to_pending(v, irq);
         set_bit(GIC_IRQ_GUEST_ENABLED, &p->status);
-- 
1.7.10.4


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