When testing the example given in the mtrace(3) man page,
no data are generated:

$ cat t_mtrace.c
#include <mcheck.h>
#include <stdio.h>
#include <stdlib.h>

int
main(void)
{
  mtrace();

  for (unsigned int j = 0; j < 2; j++)
    malloc(100);            /* Never freed--a memory leak */

  calloc(16, 16);             /* Never freed--a memory leak */
  exit(EXIT_SUCCESS);
}

$ cc -g t_mtrace.c -o t_mtrace
t_mtrace.c: In function ‘main’:
t_mtrace.c:11:5: warning: ignoring return value of ‘malloc’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
   11 |     malloc(100);            /* Never freed--a memory leak */
      |     ^~~~~~~~~~~
t_mtrace.c:13:3: warning: ignoring return value of ‘calloc’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
   13 |   calloc(16, 16);             /* Never freed--a memory leak */
      |   ^~~~~~~~~~~~~~
$ export MALLOC_TRACE=/tmp/t
$ ./t_mtrace
$ mtrace ./t_mtrace $MALLOC_TRACE
Cannot open mtrace data file at /bin/mtrace line 152, <locs> line 4.
$ ls $MALLOC_TRACE
ls: cannot access '/tmp/t': No such file or directory