Code Generation/Example 4

The Original Code

Consider the following C function:

extern int printf(const char *format, ...);
int printlist(int lo, int hi) {
  int ix = lo;
  while (ix < hi) {
    printf("%d\n", ix);
    ix++;
  }
  return ix;
}

Postfix Code

The Postfix code for the above function is as follows:

Postfix code

EXTRN printf TEXT ALIGN GLOBL printlist, FUNC LABEL printlist ENTER 4 ; ix@-4 lo@+8 hi@+12 ; int ix = lo is NOT an assignment LOCAL +8 LDINT ; read lo LOCAL -4 STINT ; write to ix ALIGN LABEL whiletest LOCAL -4 LDINT ; read ix LOCAL +12 LDINT ; read hi LT JZ whileend ; start while body ; prepare arguments for calling printf LOCAL -4 LDINT ; second printf arg: read ix ; put string literal in read-only memory RODATA ALIGN LABEL strlit SSTRING "%d\n" ; now get the address of the string literal (strlit) TEXT ADDR strlit ; first printf arg: string literal address ; args are in the stack: call the function CALL printf ; clean args TRASH 8 ; get printf return value LDFVAL32 ; get rid of return value (printf used as instruction) TRASH 4 ; increment ix LOCAL -4 LDINT ; read ix DUP32 INT 1 ADD LOCAL -4 STINT ; ix = ix + 1 ; trash old value of ix TRASH 4 ; end while body ; restart while cycle JMP whiletest ; this is the while exit point ALIGN LABEL whileend ; prepare return value LOCAL -4 LDINT ; read ix ; put it in the accumulator (register) to conform with Cdecl STFVAL32 LEAVE ; release stack frame RET ; return control to caller

Compiling and Running

To compile the Postfix code directly, pf2asm can be used:

pf2asm while.pf
yasm -felf while.asm