From b48b5b13ce4c4977008bb57d751459590e4263f0 Mon Sep 17 00:00:00 2001 From: David Given Date: Tue, 9 Aug 2022 23:32:41 +0200 Subject: [PATCH] Maybe have a working stub now. --- plat/msdos386/stub.s | 317 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 317 insertions(+) create mode 100644 plat/msdos386/stub.s diff --git a/plat/msdos386/stub.s b/plat/msdos386/stub.s new file mode 100644 index 000000000..7eb3b2ddc --- /dev/null +++ b/plat/msdos386/stub.s @@ -0,0 +1,317 @@ +# +! $Source$ +! $State$ +! $Revision$ + +! Declare segments (the order is important). + +.sect .text +.sect .rom +.sect .data +.sect .bss + +.sect .text +.use16 +exe_header: + .data2 0x5a4d ! magic number + .data2 exe_last_page ! number of bytes in last loadable page + .data2 exe_text_pages ! size of .exe, in pages + .data2 0 ! number of relocation entries + .data2 0 ! start of loadable area, in 16-byte paragraphs + .data2 exe_ram_paras ! required RAM size, in 16-byte paragraphs + .data2 exe_ram_paras ! maximum RAM siz, in 16-byte paragraphs + .data2 0 ! initial SS, relative to program + .data2 stack ! initial SP + .data2 0 ! checksum (ignored) + .data2 exe_start ! initial IP + .data2 0 ! initial CS, relative to program + .data2 0 ! offset of relocation table + .data2 0 ! overlay number + +exe_start: + ! On entry, DS=ES=PSP. Make DS=CS, so we're running in tiny mode. + + push cs + pop ds + mov (rseg), ds + mov (pspseg), es + + ! Ensure that at least two handles are available by blindly closing some. + + mov bx, 19 ! close handle + movb ah, 0x3e + int 0x21 + mov bx, 18 ! close handle + movb ah, 0x3e + int 0x21 + + ! Scan the environment to find the program name. + + eseg mov es, (0x2c) ! environment pointer segment from PSP + xor di, di + xorb al, al + mov cx, 0xffff +1: + repne scasb ! find end of next string + eseg cmpb (di), 0 + jnz 1b +2: + add di, 3 + mov si, di + repne scasb + + ! es:si now points at the program name, and es:di at one past the end. + + mov cx, di + sub cx, si + sub sp, cx ! allocate space on stack + mov di, sp ! es:si source, ds:di dest +1: + eseg movb al, (si) + inc si + movb (di), al + inc di + cmpb al, 0 + jnz 1b + + ! Open the file. (0x5f) + + mov dx, sp + mov ax, 0x3d00 + int 0x21 + jc no_file + mov (fh), ax + add sp, cx ! don't need filename any more + + ! Get the file length (== text len). + + mov bx, ax + mov ax, 0x4202 + xor cx, cx ! high offset + xor dx, dx ! low offset + int 0x21 ! lseek + mov (textlen+0), ax + mov (textlen+2), dx + + ! Initialise DPMI. + + mov ax, 0x1687 + int 0x2f + or ax, ax + jnz no_dpmi + mov (pmode_switch+0), di ! write back PMODE switch routine + mov (pmode_switch+2), es + or si, si ! do we need a DPMI private area? + jz 1f + + mov bx, si + movb ah, 0x48 + int 0x21 ! allocate memory from DOS + mov es, ax ! data area segment -> es +1: + ! Switch to protected mode. + + mov ax, 1 ! 32-bit app + callf (pmode_switch) + jc bad_dpmi + + ! We're now in protected mode. (0xa9) + + mov (psegcs), cs + mov (psegds), ds + + ! Allocate space for the code segment. + + mov ax, 0x0000 + mov cx, 1 + int 0x31 ! allocate LDT + jc bad_dpmi + mov es, ax + + mov cx, (textlen+0) + mov bx, (textlen+2) + mov ax, 0x0501 + int 0x31 ! allocate linear address + jc bad_dpmi + mov (pmemhandle+0), si + mov (pmemhandle+2), di + + mov dx, cx + mov cx, bx + mov bx, es + mov ax, 0x0007 + int 0x31 ! set segment base address + jc bad_dpmi + + mov bx, es + mov dx, (textlen+0) + mov cx, (textlen+2) + mov ax, 0x0008 + int 0x31 ! set segment limit + + mov cx, cs + and cx, 3 + shl cx, 5 + or cx, 0xc09b ! 32-bit, big, code, non-conforming, readable + mov bx, es + mov ax, 0x0009 + int 0x31 ! set descriptor access rights + + ! Load the program. (0xff) + + mov bx, (fh) + mov ax, 0x4200 + xor cx, cx ! high offset + xor dx, dx ! low offset + int 0x21 ! lseek + + o32 xor edi, edi ! destination 32-bit register +1: + movb ah, 0x3f + mov bx, (fh) + mov cx, TRANSFER_BUFFER_SIZE + mov dx, transfer_buffer + o32 push edi + call int21 ! read up to 32kB into transfer buffer + o32 pop edi + cmp ax, 0 + je 2f + + o32 movzx ecx, ax ! number of bytes read + o32 mov esi, transfer_buffer + o32 rep movsb + jmp 1b +2: + + ! Close the file. + + movb ah, 0x3e + mov bx, (fh) + int 0x21 ! close + + ! Jump to the new segment and enter 32-bit mode! + + o32 mov eax, (pmemhandle) + o32 movzx ebx, (rseg) + push es + push text_top + retf + +bad_dpmi: + mov si, bad_dpmi_msg + jmp exit_with_error + +no_file: + mov si, no_file_msg + jmp exit_with_error + +no_dpmi: + mov si, no_dpmi_msg + ! fall through + +! Displays the message in si and exits. +! This uses a loop because from protected mode any interrupt which +! takes a pointer parameter requires special treatment. +exit_with_error: + movb dl, (si) + cmpb dl, 0 + je 1f + inc si + + movb ah, 2 + int 0x21 ! print character + jmp exit_with_error +1: + mov ax, 0x4cff + int 0x21 ! terminate with error code al + +pmode: + .use32 + mov ax, 0x4c00 + int 0x21 + .use16 + + ! Simulate DOS interrupt. +int21: + mov (dpmi_eax), ax + mov (dpmi_ebx), bx + mov (dpmi_ecx), cx + mov (dpmi_edx), dx + mov ax, (rseg) + mov (dpmi_ds), ax + push es + push ds + xor ax, ax + mov (dpmi_ss), ax ! zero stack: DPMI host allocates one. + mov (dpmi_sp), ax + push ds + pop es + mov di, dpmi_edi + mov ax, 0x300 + mov bx, 0x21 + int 0x31 ! simulate DOS interrupt + pop ds + pop es + mov ax, (dpmi_eax) + mov bx, (dpmi_ebx) + mov cx, (dpmi_ecx) + mov dx, (dpmi_edx) + push (dpmi_flags) + popf + ret + +bad_dpmi_msg: + .asciz "DPMI error during setup" +no_file_msg: + .asciz "Couldn't open .exe" +no_dpmi_msg: + .asciz "No DPMI host installed" +text_top: + +exe_text_pages = [text_top - exe_header + 511] / 512 +exe_last_page = [text_top - exe_header] % 512 + +.sect .rom + +.sect .bss +bss_start: + +dpmi_edi: .space 4 +dpmi_esi: .space 4 +dpmi_ebp: .space 4 + .space 4 ! reserved +dpmi_ebx: .space 4 +dpmi_edx: .space 4 +dpmi_ecx: .space 4 +dpmi_eax: .space 4 +dpmi_flags: .space 2 +dpmi_es: .space 2 +dpmi_ds: .space 2 +dpmi_fs: .space 2 +dpmi_gs: .space 2 +dpmi_ip: .space 2 +dpmi_cs: .space 2 +dpmi_sp: .space 2 +dpmi_ss: .space 2 + +pmode_switch: .space 4 +rseg: .space 2 ! real mode +pspseg: .space 2 ! real mode +psegcs: .space 2 ! protected mode 16-bit code segment +psegds: .space 2 ! protected mode 16-bit data segment +pmemhandle: .space 4 ! protected mode linear memory handle +fh: .space 2 +textlen: .space 4 + + .space 128 +stack: + +TRANSFER_BUFFER_SIZE = 32*1024 +transfer_buffer: + .space TRANSFER_BUFFER_SIZE + +bss_top: +exe_ram_paras = [bss_top - bss_start + 15] / 16 + +! vim: ts=4 sw=4 et ft=asm +