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

["Andreas Färber" <afaerber@suse.de>]

Am 19.07.2013 04:26, schrieb Mike Qiu:
> 于 2013/7/19 1:14, Andreas Färber 写道:
>> There's some typos in the commit message, but the change looks okay to
>> me - although there were discussions to catch this on the memory API
>> side of things instead.
> You mean this patch: see below:
> 
> exec: Support 64-bit operations in address_s

No, I don't. There were other segfault avoidance patches like yours over
the past months - they're all fixing individual segfault symptoms.
Question for Paolo is whether we want to continue to discover them one
by one or whether to implement a fallback inside memory code if .read or
.write is NULL.

Andreas

> 
> BTW, this bug has been opened before?
> 
> Thanks
> Mike
>>
>> Regards,
>> Andreas
>>
>>> Thanks
>>> Mike
>>> 2013/7/16 11:50, Mike Qiu wrote:
>>>> 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,
>>>
>>
> 


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