Patchwork [13/16] kvm: Comparison with ioctl number macros needs to be unsigned

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Submitter Alexander Graf
Date March 15, 2012, 12:14 p.m.
Message ID <1331813662-15141-14-git-send-email-agraf@suse.de>
Download mbox | patch
Permalink /patch/146936/
State New
Headers show

Comments

Alexander Graf - March 15, 2012, 12:14 p.m.
From: David Gibson <david@gibson.dropbear.id.au>

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 <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>
---
 kvm-all.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

Patch

diff --git a/kvm-all.c b/kvm-all.c
index 42e5e23..ba2cee1 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;