Loading into Array causes Stack Smashing while having enough space?

Question

When executing the following code I get a Stack Smashing error.

const uint size = 62;

...
for (int i=0; i < 10; ++i){
    // mask = elements != zero
    // input = epi32 m512 data containing 1 byte values
    _mm512_mask_compress_epi32(input, mask, input);
    // get just elements != 0 as previous mask. 
    __mmask16 mask1 = _mm512_cmpneq_epi32_mask(compressed, _mm512_setzero_epi32());
    // append the non-zero elements to the uchar* 
    _mm512_mask_cvtusepi32_storeu_epi8((uchar*)str+pos, mask1, compressed); // uncommenting = no error, truncating mask = no error

     // add size of the inserted elements by counting 1's in mask
     pos += sizeOfInsertion;

     // print the position of the pointer AFTER storing
     void* pp = (void*) ((uchar*) str + pos);
     std::cout << pp << std::endl;
}

To investigate this issue, I was checking the position of the pointer while inserting the elements. At beginning (pointing to str[0]) I have 0x7ffce3468d30, at the end 0x7ffce3468d69. Subtracting these addresses I get 3E = 62. So it should fit inside the declared array. Shifting the mask by 1 (truncating one element), it doesn't throw an error.

Answer 1

The failure was in the compression. I didn't mind zeroing the values not matching the mask, so data wasn't stored contiguously and the stack was therefore overflowing.

In short:

_mm512_maskz_compress_epi32(mask, input);

made it work.