[Qemu-devel] [PATCH] Bug Fix:Segmentation fault when use usb-ehci device

[Mike Qiu <qiudayu@linux.vnet.ibm.com>]

For usb-ehci in qemu, its caps just has read() operation,
the write() operation does not exist.

This cause a Segmentation fault when use usb-ehci device in ppc64
platform.

here is gdb output:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x3fffa7fcef20 (LWP 6793)]
0x00000000103f5244 in memory_region_oldmmio_write_accessor
(opaque=0x113e9e78, addr=9, value=0x3fffa7fce088,
size=1, shift=0, mask=255) at /home/Mike/qemu-impreza/memory.c:384
384  mr->ops->old_mmio.write[ctz32(size)](mr->opaque, addr, tmp);
(gdb) p *mr->ops
$1 = {read = @0x10716f68: 0x1020699c <ehci_caps_read>, write = 0,
   endianness = DEVICE_LITTLE_ENDIAN, valid = {min_access_size = 1,
   max_access_size = 4, unaligned = false, accepts = 0}, impl =
   {min_access_size = 1, max_access_size = 1, unaligned = false},
   old_mmio = {read = {0, 0, 0}, write = {0, 0, 0}}}

Becasue function write() of mr->ops has not been implement, in
function memory_region_dispatch_write(), it call
oldmmio write accessor, but at the same time old_mmio still not
been implement by default.

That is the root cause of the Segmentation fault.

To solve this problem, add empty function: ehci_caps_write()

Signed-off-by: Mike Qiu <qiudayu@linux.vnet.ibm.com>
---
 hw/usb/hcd-ehci.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/hw/usb/hcd-ehci.c b/hw/usb/hcd-ehci.c
index 67e4b24..6c8a439 100644
--- a/hw/usb/hcd-ehci.c
+++ b/hw/usb/hcd-ehci.c
@@ -1072,6 +1072,12 @@ static void ehci_port_write(void *ptr, hwaddr addr,
     trace_usb_ehci_portsc_change(addr + s->portscbase, addr >> 2, *portsc, old);
 }
 
+static void ehci_caps_write(void *ptr, hwaddr addr, uint64_t val,
+                           unsigned size)
+{
+    /* nothing */
+}
+
 static void ehci_opreg_write(void *ptr, hwaddr addr,
                              uint64_t val, unsigned size)
 {
@@ -2380,6 +2386,7 @@ static void ehci_frame_timer(void *opaque)
 
 static const MemoryRegionOps ehci_mmio_caps_ops = {
     .read = ehci_caps_read,
+    .write = ehci_caps_write,
     .valid.min_access_size = 1,
     .valid.max_access_size = 4,
     .impl.min_access_size = 1,
-- 
1.7.10.1