From 92e4b519e0808948ae4bc710fb1db7d3cc2245a1 Mon Sep 17 00:00:00 2001 From: David Gibson Date: Wed, 7 Mar 2012 14:41:09 +0000 Subject: [PATCH] kvm: Comparison with ioctl number macros needs to be unsigned In kvm-all.c we store an ioctl cmd number in the irqchip_inject_ioctl field of KVMState, which has type 'int'. This seems to make sense since the ioctl() man page says that the cmd parameter has type int. However, the kernel treats ioctl numbers as unsigned - sys_ioctl() takes an unsigned int, and the macros which generate ioctl numbers expand to unsigned expressions. Furthermore, some ioctls (IOC_READ ioctls on x86 and IOC_WRITE ioctls on powerpc) have bit 31 set, and so would be negative if interpreted as an int. This has the surprising and compile-breaking consequence that in kvm_irqchip_set_irq() where we do: return (s->irqchip_inject_ioctl == KVM_IRQ_LINE) ? 1 : event.status; We will get a "comparison is always false due to limited range of data type" warning from gcc if KVM_IRQ_LINE is one of the bit-31-set ioctls, which it is on powerpc. So, despite the fact that the man page and posix say ioctl numbers are signed, they're actually unsigned. The kernel uses unsigned, the glibc header uses unsigned long, and FreeBSD, NetBSD and OSX also use unsigned long ioctl numbers in the code. Therefore, this patch changes the variable to be unsigned, fixing the compile. Signed-off-by: David Gibson Signed-off-by: Alexander Graf --- kvm-all.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/kvm-all.c b/kvm-all.c index 42e5e23d5d..ba2cee10f2 100644 --- a/kvm-all.c +++ b/kvm-all.c @@ -79,7 +79,10 @@ struct KVMState int pit_state2; int xsave, xcrs; int many_ioeventfds; - int irqchip_inject_ioctl; + /* The man page (and posix) say ioctl numbers are signed int, but + * they're not. Linux, glibc and *BSD all treat ioctl numbers as + * unsigned, and treating them as signed here can break things */ + unsigned irqchip_inject_ioctl; #ifdef KVM_CAP_IRQ_ROUTING struct kvm_irq_routing *irq_routes; int nr_allocated_irq_routes;