| Message ID | 1331167272-9800-2-git-send-email-david@gibson.dropbear.id.au |
|---|---|
| State | New |
| Headers | show |
On 08.03.2012, at 01:41, David Gibson wrote: > 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. > > Cc: Avi Kivity <avi@redhat.com> > Cc: Marcelo Tossatti <mtossatti@redhat.com> > > Signed-off-by: David Gibson <david@gibson.dropbear.id.au> I picked that one into ppc-next, as without compilation on ppc breaks for me. I haven't touched the other 3 patches in the set though. Alex PS: These 4 patches don't target a single maintainer. Thus it's better to not send them as a patch set :).
diff --git a/kvm-all.c b/kvm-all.c index 77eadf6..a5727a3 100644 --- a/kvm-all.c +++ b/kvm-all.c @@ -78,7 +78,10 @@ struct KVMState int pit_in_kernel; 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;
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. Cc: Avi Kivity <avi@redhat.com> Cc: Marcelo Tossatti <mtossatti@redhat.com> Signed-off-by: David Gibson <david@gibson.dropbear.id.au> --- kvm-all.c | 5 ++++- 1 files changed, 4 insertions(+), 1 deletions(-)