/in/foo.c: In function 'main':
/in/foo.c:8:3: warning: implicit declaration of function 'ptintf' [-Wimplicit-function-declaration]
   ptintf("****\n");
   ^~~~~~
/tmp/ccebSMm0.o: In function `main':
foo.c:(.text.startup+0x32): undefined reference to `ptintf'
collect2: error: ld returned 1 exit status