Passing dynamic array of structs to GPU kernel

Question

I try to pass my dynamic array of structs to kernel but it doesn't works. I get - "Segmentation fault (core dumped)"

My code - EDITED

#include <stdio.h>
#include <stdlib.h>

struct Test {
    unsigned char *array;
};

__global__ void kernel(Test *dev_test) {
}

int main(void) {

    int n = 4;
    int size = 5;
    unsigned char *array[size];
    Test *dev_test;

    //   allocate for host
    Test *test = (Test*)malloc(sizeof(Test)*n);
    for(int i = 0; i < n; i++)
    test[i].array =  (unsigned char*)malloc(size);


    //  fill data
    for(int i=0; i<n; i++) {
        unsigned char temp[] = { 'a', 'b', 'c', 'd' , 'e' };
        memcpy(test[i].array, temp, size);
    }

    //  allocate for gpu
    cudaMalloc((void**)&dev_test, n * sizeof(Test));
    for(int i=0; i < n; i++) {
        cudaMalloc((void**)&(array[i]), size * sizeof(unsigned char));
        cudaMemcpy(&(dev_test[i].array), &(array[i]), sizeof(unsigned char *), cudaMemcpyHostToDevice);
    }

    kernel<<<1, 1>>>(dev_test);

    return 0;
}

How correctly I should allocate gpu memory and copy data to this memory?

Standard Warning : Please do not cast the return value of malloc() and family in C. — Sourav Ghosh
– Sourav Ghosh, Commented May 5, 2015 at 14:01
@SouravGhosh although the question is currently tagged c, the context here is actually c++. — Robert Crovella
– Robert Crovella, Commented May 5, 2015 at 14:10

Community · Accepted Answer · 2017-05-23 12:06:33Z

4

You need to allocate memory for struct member array.

Test *test = malloc(sizeof(Test)*n);
for(int i = 0; i < n; i++)   
    test[i]->array =  malloc(size);

I would suggest to read this answer to cope up with other issues after this fix.

edited May 23, 2017 at 12:06

CommunityBot

11 silver badge

answered May 5, 2015 at 14:04

haccks

107k28 gold badges181 silver badges274 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Robert Crovella Over a year ago

And when you've fixed this issue, which is indeed the source of the seg fault (has nothing to do with CUDA) you'll run into the next problem with this code (if you attempt to use the data in the kernel) which will be a duplicate of what is discussed here.

haccks Over a year ago

@RobertCrovella; Agreed.

Bakus123 Over a year ago

@RobertCrovella, thanks I improved my code according to your instructions. But how can I copy data from test[i].array to dev_test[i].array? And how looks deallocation of memory in this case?

Robert Crovella Over a year ago

refer to the duplicate question I linked and study the linked examples. You have copied the pointers but not the actual data they point to. If you still need help, ask a new question. This one has already been answered. SO is not a chat room, and if you continue to modify your question as you incorporate the feedback given in the answers, it's going to be very confusing.

X3liF · Accepted Answer · 2015-05-05 15:36:32Z

2

what is your card ? if your card support compute capability >= 3.0, try the unified memory system , to have same data in host/device memory

you can have a look here :

it should maybe look like this one :

    int main(void) {
int n = 4;
int size = 5;
Test *test;
cudaMallocManaged(&test, n * size);
unsigned char values[] = { 'a', 'b', 'c', 'd' , 'e' };
for(int i=0; i<n; i++) 
{
    unsigned char* temp;
    cudaMallocManaged(&temp, size*sizeof(char) );
    memcpy(temp, values, sizeof(values) );
}
// avoid copy code, makes a deep copy of objects
kernel<<<1, 1>>>(test);
return 0;
    }

And i hope you know it, but Don't forget do call cudaFree & delete/free on allocated memory. (better to use std::vector and use data() to access to raw pointer)

edited May 5, 2015 at 15:36

answered May 5, 2015 at 14:55

X3liF

1,0726 silver badges10 bronze badges

Collectives™ on Stack Overflow

Passing dynamic array of structs to GPU kernel

2 Answers 2

4 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related