OpenCL: using struct as kernel argument

Question

Can I use struct as OpenCL kernel argument?

I want to use struct type as OpenCL kernel argument in NVIDIA OpenCL 1.2 (NVIDIA driver 352.39)

I tried, but it makes CL_OUT_OF_RESOURCE error.

What is wrong in my code??

[for struct definition]

/* struct type definition */
typedef struct _st_foo
{
    int aaa;
    int bbb;
     .....
    int zzz;
}st_foo;      // st_foo doesn't have any pointer members

[Host code]

/* OpenCL initalize... */

st_foo stVar;

cl_mem cm_buffer;
cm_buffer = clCreateBuffer(cxContext, CL_MEM_READ_ONLY, sizeof(st_foo), NULL, NULL);
clSetKernelArg(ckKernel, 0, sizeof(cl_mem), (void*)&cm_buffer);
clEnqueueWriteBuffer(cqueue, cm_buffer, CL_TRUE, 0, sizeof(st_foo), &stVar, 0, NULL, NULL);

[Kernel code]

__kernel void testfunction(__global const st_foo *stVar)
{
    printf("stVar->aaa=%d\n", stVar->aaa);
}

Answer 1

It is not safe to declare structs in OpenCL if you are not using the OpenCL datatypes. And also, alignment may be an issue, force a packet alignment in the Host/Device compiler.

You should declare your structs as:

[Host]

typedef struct __attribute__ ((packed)) _st_foo
{
    cl_int aaa;
    cl_int bbb;
     .....
    cl_int zzz;
}st_foo;

[Device]

typedef struct __attribute__ ((packed)) _st_foo
{
    int aaa;
    int bbb;
     .....
    int zzz;
};

Aditionally, if you just want a single parameter, not an array of structs, then just pass it in as:

clSetKernelArg(ckKernel, 0, sizeof(mystruct), mystruct);