odd SIGBUS

shm_mmap_test.c

#include <fcntl.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <stdlib.h>
#include <string.h>

int main()
{

  int fileDescriptor;
  int size = 4*1024*1024;

  fileDescriptor = shm_open("/test", O_CREAT | O_CLOEXEC | O_RDWR, S_IRUSR | S_IWUSR);
  ftruncate(fileDescriptor, size);

  void* data = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, fileDescriptor, 0);

  memset(data, 'a', size);
  return 0;
}

OK it is a system integration issue, the tmpfs of /dev/shm has a mount option size=1M which can't have a 4M shared memory.