;; alloca386.s 1.2 ;; GNU-compatible stack allocation function for Xenix/386. ;; Written by Chip Salzenberg at ComDev. ;; Last modified 90/01/11 ;;> Is your alloca clearly better than the one in i386-alloca.s? I haven't ;;> looked at either. ;; ;;They're different because Xenix/386 has a different assembler. SCO ;;Xenix has the Microsoft C compiler and the Microsoft macro assembler, ;;called "masm". MASM's assembler syntax is quite different from AT&T's ;;in all sorts of ways. Xenix people can't use the AT&T version. ;;-- ;;Chip Salzenberg at ComDev/TCT <chip@tct.uucp>, <uunet!ateng!tct!chip> TITLE $alloca386 .386 DGROUP GROUP CONST, _BSS, _DATA _DATA SEGMENT DWORD USE32 PUBLIC 'DATA' _DATA ENDS _BSS SEGMENT DWORD USE32 PUBLIC 'BSS' _BSS ENDS CONST SEGMENT DWORD USE32 PUBLIC 'CONST' CONST ENDS _TEXT SEGMENT DWORD USE32 PUBLIC 'CODE' ASSUME CS: _TEXT, DS: DGROUP, SS: DGROUP, ES: DGROUP PUBLIC _alloca _alloca PROC NEAR ; Get argument. pop edx ; edx -> return address pop eax ; eax = amount to allocate ; Validate allocation amount. add eax,3 and eax,not 3 cmp eax,0 jg aa_size_ok mov eax,4 aa_size_ok: ; Allocate stack space. mov ecx,esp ; ecx -> old stack pointer sub esp,eax ; perform allocation mov eax,esp ; eax -> new stack pointer ; Copy the three saved register variables from old stack top to new stack top. ; They may not be there. So we waste twelve bytes. Big fat hairy deal. push DWORD PTR 8[ecx] push DWORD PTR 4[ecx] push DWORD PTR 0[ecx] ; Push something so the caller can pop it off. push eax ; Return to caller. jmp edx _alloca ENDP _TEXT ENDS END