| 1,8 → 1,11 |
|---|
| ; minimalist Watcom C startup routine - TINY memory model ONLY - (.COM files) |
| ; kindly contributed by Bernd Boeckmann |
| |
| .8086 |
| |
| STACK_SIZE = 2048 |
| |
| dgroup group _TEXT,_DATA,CONST,CONST2,_STACK,_BSS |
| DGROUP group _TEXT,_DATA,CONST,CONST2,_BSS,_EOF |
| |
| extrn "C",main : near |
| |
| 23,10 → 26,13 |
|---|
| ; for this reasons it is beneficial to resize the memory block we occupy |
| ; into a more reasonable value |
| |
| ; step 1: if SP is higher than my top_of_stack, then set SP explicitely |
| cmp sp, top_of_stack |
| jle resizemem |
| mov sp, top_of_stack |
| ; step 1: if SP > COM size + stack size, then set SP explicitely |
| ; POTENTIAL error: offset DGROUP:_EOF + STACK_SIZE may overflow! |
| ; Has to be detected at linking stage, but WLINK does not catch it. |
| adjustsp: |
| cmp sp, offset DGROUP:_EOF + STACK_SIZE |
| jbe resizemem ; JBE instead of JLE (unsigned comparison!) |
| mov sp, offset DGROUP:_EOF + STACK_SIZE |
| |
| ; step 2: resize our memory block to sp bytes (ie. sp/16 paragraphs) |
| resizemem: |
| 39,6 → 45,14 |
|---|
| inc bx |
| int 21h |
| |
| ; clear _BSS to be ANSI C conformant |
| mov di, offset DGROUP:_BSS |
| mov cx, offset DGROUP:_EOF |
| sub cx, di |
| xor al, al |
| cld |
| rep stosb |
| |
| call main |
| mov ah, 4ch |
| int 21h |
| 48,29 → 62,25 |
|---|
| ;__STK: |
| ; ret |
| |
| _DATA segment word public 'DATA' |
| _DATA ends |
| _DATA segment word public 'DATA' |
| _DATA ends |
| |
| CONST segment word public 'DATA' |
| CONST ends |
| CONST segment word public 'DATA' |
| CONST ends |
| |
| CONST2 segment word public 'DATA' |
| CONST2 ends |
| CONST2 segment word public 'DATA' |
| CONST2 ends |
| |
| _BSS segment word public 'BSS' |
| _BSS ends |
| _BSS segment word public 'BSS' |
| _BSS ends |
| |
| _STACK segment para public 'BSS' |
| db (STACK_SIZE) dup(0) ; set this explicitely to zero, otherwise |
| ; static variables are not properly |
| ; initialized. this makes the COM file |
| ; much bigger, but it is irrelevant if it |
| ; is UPXed afterwards anyway. If you care, |
| ; then you may zero out this area in |
| ; code instead (before calling main) |
| top_of_stack: |
| _STACK ends |
| ; _EOF should be the last segment in .COM (see linker memory map) |
| ; if not, someone introduced other segments, or startup.obj is not the first |
| ; linker object file |
| _EOF segment word public |
| _EOF ends |
| |
| _TEXT ends |
| |
| end _cstart_ |
| |