Hi,
On Fri, Dec 09, 2016 at 06:49:56AM +0000, Yang, Rong R wrote:
> The change is for the case that param_value_size > sizeof(device->FIELD).
> For example:
> cl_ulong max_alloc_size;
> clGetDeviceInfo(device, CL_DEVICE_MAX_MEM_ALLOC_SIZE,
> sizeof(max_alloc_size), &max_alloc_size, NULL);
> param_value_size is 8, if beignet's device->max_alloc_size is size_t,
> sizeof(device->max_alloc_size) is 4 in i386 systems.
Yes, but this has been fixed now.
> Because max_alloc_size hasn't been initialized, is garbage, and
> memcpy(param_value, &device->FIELD, sizeof device->FIELD);
> only copy the low 4 bytes, the high 4 bytes is still garbage.
> For example max_alloc_size is 0xdeaddeaddeaddead before call clGetDeviceInfo,
> and device-> max_alloc_size is 0x40000000,
> After clGetDeviceInfo, max_alloc_size's value is 0xdeaddead40000000.
Right, but the returned size value is 4, so the program should know that
there was a communication error, and bail out anyway, because if Beignet
doesn't return sizeof(cl_ulong) there, then obviously it hasn't stored a
cl_ulong, so the result cannot be interpreted that way.
If a program doesn't do that check, it is broken. I cannot expect
__uint128_t max_alloc_size;
clGetDeviceInfo(device, CL_DEVICE_MAX_MEM_ALLOC_SIZE, sizeof(max_alloc_size),
&max_alloc_size, NULL);
to work either. People need to write this out completely, as
__uint128_t max_alloc_size;
cl_uint max_alloc_size_size;
int error = clGetDeviceInfo(device, CL_DEVICE_MAX_MEM_ALLOC_SIZE, sizeof
max_alloc_size, &max_alloc_size, &max_alloc_size_size);
if(error != CL_SUCCESS)
goto error;
if(max_alloc_size_size != sizeof max_alloc_size)
goto error;
and if they don't, I want valgrind to say "btw, they are using a value with
uninitialized bits here."
> So add memset(param_value, 0, param_value_size) to clear param_value, the
> param_value's size is param_value_size, I think it is safe.
Safe, yes, because the spec doesn't say what should happen to the rest of
the buffer (so overwriting with zeros is fine), but also unnecessary.
Simon
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