backend: i386 어셈블리를 내고 Windows 11 실행 파일을 만든다

fec --emit-asm -> wasm -> wlink -> .exe. 툴체인은 고정된 Open Watcom 그대로다.

레지스터 할당기가 없다. 임시값마다 스택 슬롯을 주고, 명령마다 피연산자를
고정 레지스터로 읽어 계산하고 다시 저장한다. 느린 코드지만 명백히 옳은
코드이고, 옳은 것이 먼저다. 나중에 할당기를 끼워도 나머지는 모른다 --
임시값이 어디 사는지만 바뀐다.

런타임 fec/rt/start.asm 은 진입 스텁과 fe_trap 이다. trap 은 이유와 파일과
줄을 stderr 에 쓰고 3으로 끝낸다.

처음으로 Ferro 프로그램이 실행됐다:

  1..10 합         -> 55
  (7*6-2)/4        -> 10
  루프+호출+분기   -> 1

tests/build.py 가 컴파일하고 링크하고 돌린다.

fec/rt/start.asm

@@ -0,0 +1,134 @@
+; Ferro runtime: process entry and the trap handler.
+;
+; The entry point calls the program's `main` and hands its result to
+; ExitProcess, so a Ferro program is an ordinary console executable.
+; `fe_trap` prints where the program stopped and why, then exits 3.
+
+.386
+.model flat
+
+extern _ExitProcess@4 : near
+extern _GetStdHandle@4 : near
+extern _WriteFile@20 : near
+extern fe_main_ : near
+
+_DATA segment dword public 'DATA'
+
+reasons     dd  offset r_bounds, offset r_overflow, offset r_divide
+            dd  offset r_unreach, offset r_explicit
+r_bounds    db  'index out of bounds',0
+r_overflow  db  'integer overflow',0
+r_divide    db  'divide by zero',0
+r_unreach   db  'reached unreachable code',0
+r_explicit  db  'trap',0
+r_unknown   db  'trap',0
+prefix      db  'ferro: ',0
+at_word     db  ' at ',0
+colon       db  ':',0
+newline     db  13,10,0
+numbuf      db  16 dup(0)
+written     dd  0
+
+_DATA ends
+
+_TEXT segment dword public 'CODE'
+
+; write_cstr(esi = pointer to a NUL-terminated string) -> void
+write_cstr proc near
+        push    ebp
+        mov     ebp, esp
+        push    ebx
+        push    esi
+        push    edi
+        mov     edi, esi
+        xor     ecx, ecx
+count_loop:
+        cmp     byte ptr [edi], 0
+        je      count_done
+        inc     edi
+        inc     ecx
+        jmp     count_loop
+count_done:
+        test    ecx, ecx
+        je      write_done
+        push    -11                     ; STD_ERROR_HANDLE
+        call    _GetStdHandle@4
+        push    0                       ; lpOverlapped
+        push    offset written
+        push    ecx
+        push    esi
+        push    eax
+        call    _WriteFile@20
+write_done:
+        pop     edi
+        pop     esi
+        pop     ebx
+        mov     esp, ebp
+        pop     ebp
+        ret
+write_cstr endp
+
+; write_uint(eax = value) -> void
+write_uint proc near
+        push    ebp
+        mov     ebp, esp
+        push    ebx
+        mov     edi, offset numbuf + 15
+        mov     byte ptr [edi], 0
+        mov     ebx, 10
+digit_loop:
+        xor     edx, edx
+        div     ebx
+        add     dl, '0'
+        dec     edi
+        mov     [edi], dl
+        test    eax, eax
+        jnz     digit_loop
+        mov     esi, edi
+        call    write_cstr
+        pop     ebx
+        mov     esp, ebp
+        pop     ebp
+        ret
+write_uint endp
+
+; fe_trap(reason, file, line) -- cdecl, never returns
+public fe_trap
+fe_trap proc near
+        push    ebp
+        mov     ebp, esp
+        mov     esi, offset prefix
+        call    write_cstr
+        mov     eax, [ebp+8]            ; reason
+        cmp     eax, 5
+        jb      reason_ok
+        mov     esi, offset r_unknown
+        jmp     reason_write
+reason_ok:
+        mov     esi, [reasons + eax*4]
+reason_write:
+        call    write_cstr
+        mov     esi, offset at_word
+        call    write_cstr
+        mov     esi, [ebp+12]           ; file
+        call    write_cstr
+        mov     esi, offset colon
+        call    write_cstr
+        mov     eax, [ebp+16]           ; line
+        call    write_uint
+        mov     esi, offset newline
+        call    write_cstr
+        push    3
+        call    _ExitProcess@4
+fe_trap endp
+
+public fe_start_
+fe_start_ proc near
+        call    fe_main_
+        push    eax
+        call    _ExitProcess@4
+fe_start_ endp
+
+_TEXT ends
+
+end fe_start_