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[PATCH 04/13] vfio-pci: use 32-bit comparisons for register address for gcc-4.5

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  [PATCH 04/13] vfio-pci: use 32-bit comparisons for register address for gcc-4.5 Arnd Bergmann <arnd@arndb.de> - 2016-12-16 12:00 +0100
    Re: [PATCH 04/13] vfio-pci: use 32-bit comparisons for register  address for gcc-4.5 Alex Williamson <alex.williamson@redhat.com> - 2016-12-16 16:40 +0100
      Re: [PATCH 04/13] vfio-pci: use 32-bit comparisons for register address for gcc-4.5 Arnd Bergmann <arnd@arndb.de> - 2016-12-16 21:00 +0100

#1543363 — [PATCH 04/13] vfio-pci: use 32-bit comparisons for register address for gcc-4.5

Using ancient compilers (gcc-4.5 or older) on ARM, we get a link
failure with the vfio-pci driver:

ERROR: "__aeabi_lcmp" [drivers/vfio/pci/vfio-pci.ko] undefined!

The reason is that the compiler tries to do a comparison of
a 64-bit range. This changes it to convert to a 32-bit number
explicitly first, as newer compilers do for themselves.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/vfio/pci/vfio_pci_rdwr.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/vfio/pci/vfio_pci_rdwr.c b/drivers/vfio/pci/vfio_pci_rdwr.c
index 5ffd1d9ad4bd..357243d76f10 100644
--- a/drivers/vfio/pci/vfio_pci_rdwr.c
+++ b/drivers/vfio/pci/vfio_pci_rdwr.c
@@ -193,7 +193,10 @@ ssize_t vfio_pci_vga_rw(struct vfio_pci_device *vdev, char __user *buf,
 	if (!vdev->has_vga)
 		return -EINVAL;
 
-	switch (pos) {
+	if (pos > 0xbfffful)
+		return -EINVAL;
+
+	switch ((u32)pos) {
 	case 0xa0000 ... 0xbffff:
 		count = min(count, (size_t)(0xc0000 - pos));
 		iomem = ioremap_nocache(0xa0000, 0xbffff - 0xa0000 + 1);
-- 
2.9.0

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#1543528 — Re: [PATCH 04/13] vfio-pci: use 32-bit comparisons for register address for gcc-4.5

On Fri, 16 Dec 2016 11:56:25 +0100
Arnd Bergmann <arnd@arndb.de> wrote:

> Using ancient compilers (gcc-4.5 or older) on ARM, we get a link
> failure with the vfio-pci driver:
> 
> ERROR: "__aeabi_lcmp" [drivers/vfio/pci/vfio-pci.ko] undefined!
> 
> The reason is that the compiler tries to do a comparison of
> a 64-bit range. This changes it to convert to a 32-bit number
> explicitly first, as newer compilers do for themselves.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/vfio/pci/vfio_pci_rdwr.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_rdwr.c b/drivers/vfio/pci/vfio_pci_rdwr.c
> index 5ffd1d9ad4bd..357243d76f10 100644
> --- a/drivers/vfio/pci/vfio_pci_rdwr.c
> +++ b/drivers/vfio/pci/vfio_pci_rdwr.c
> @@ -193,7 +193,10 @@ ssize_t vfio_pci_vga_rw(struct vfio_pci_device *vdev, char __user *buf,
>  	if (!vdev->has_vga)
>  		return -EINVAL;
>  
> -	switch (pos) {
> +	if (pos > 0xbfffful)
> +		return -EINVAL;
> +
> +	switch ((u32)pos) {
>  	case 0xa0000 ... 0xbffff:
>  		count = min(count, (size_t)(0xc0000 - pos));
>  		iomem = ioremap_nocache(0xa0000, 0xbffff - 0xa0000 + 1);

Acked-by: Alex Williamson <alex.williamson@redhat.com>

Would you like me to pull this one patch in through the vfio tree?
Thanks,

Alex

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#1543721

On Friday, December 16, 2016 8:30:56 AM CET Alex Williamson wrote:
> 
> Acked-by: Alex Williamson <alex.williamson@redhat.com>
> 
> Would you like me to pull this one patch in through the vfio tree?
> Thanks,

If you think the patch is appropriate, please merge it.

I originally just posted this as illustration to raise the
question of whether we actually want to support gcc-4.5,
from the feedback so far it does seem like the answer is yes,
and we will need it.

	Arnd

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