DEFINITION MODULE Runtime ;

(* 8086 runtime library for TP3-compiled programs.

   The original embeds its runtime in the compiler's own code segment and
   copies it to the front of the generated code buffer (TPSRC7 "copyrt":
   "MOV CX,#start / REPZ MOVS.B" with SI=DI=0, then "MOV pc,#$2D7C" so the
   generated program starts past it; the .COM writer emits the runtime as a
   block ahead of the program).  Same shape here: RT_Build assembles the
   library into rt[0..RT_Size-1], the compiler copies it to the front of its
   code buffer and starts pc/dc past it, so the runtime's own data lives at
   low, link-time-constant addresses and needs no relocation.

   Entry offsets are *derived* from where the code actually lands, not
   hardcoded - see RT_Entry.  Everything the compiler calls is reached by a
   relative CALL, and both sides shift by the same runtime size, so the
   displacement arithmetic in EmCall is unaffected by the runtime being
   prepended. *)

FROM SYSTEM IMPORT BYTE ;

CONST
   (* entry selectors for RT_Entry *)
   E_InitMem = 0 ;  E_ProgEnd = 1 ;  E_StackChk = 2 ;
   E_WrInt   = 3 ;  E_WrChar  = 4 ;  E_WrBool  = 5 ;
   E_WrReal  = 6 ;  E_WrLn    = 7 ;
   E_RdInt   = 8 ;  E_RdChar  = 9 ;  E_RdBool  = 10 ;
   E_RdLn    = 11 ; E_Halt    = 12 ; E_WrInl   = 13 ;

PROCEDURE RT_Build () ;
(* assemble the runtime; idempotent, called once at Compile time *)

PROCEDURE RT_Size () : CARDINAL ;
(* size of the runtime in bytes - the offset at which the generated program
   starts inside the image *)

PROCEDURE RT_Byte (i : CARDINAL) : BYTE ;
(* i-th runtime byte, 0 past the end, for hex dumps *)

PROCEDURE RT_Entry (i : CARDINAL) : CARDINAL ;
(* offset of entry i (an E_* selector) inside the runtime; 0 if unknown *)

PROCEDURE RT_CodeEnd () : CARDINAL ;
(* offset where the code stops and the runtime's data block starts.  Bytes
   from here on are strings and scratch, so disassembling them is
   meaningless; tests use this to sweep the code region only. *)

END Runtime.