use Devel::Peek;
my $x = "";
Dump $x;
ddd($x);
Dump $x;

use Inline 'C' => <<'CODE';
int ddd(SV* x){
     char* dx = "dddddd\n";
     char* bbb=NULL;
     Newx(bbb, 8, char);
     Copy(dx, bbb, 8, char);
     printf("string dx is %p \n", dx);
     printf("string bbb is %p \n", bbb);
 //  sv_setpvn(x, dx, 8);       #copy string to a SV
 //  sv_usepvn(x, dx, 8);       #segment fault!
     sv_usepvn(x, bbb, 8);      #"attach" to a SV
     return 0;
 }
CODE
########## output ##########
SV = PV(0x559f4143cfd0) at 0x559f41461018
  REFCNT = 1
  FLAGS = (POK,IsCOW,pPOK)
  PV = 0x559f414d58a0 ""\0
  CUR = 0
  LEN = 10
  COW_REFCNT = 1
string dx is 0x7f12ed54f8d8
string bbb is 0x559f41462ad0
SV = PV(0x559f4143cfd0) at 0x559f41461018
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x559f41462ad0 "dddddd\n\0"\0
  CUR = 8
  LEN = 16