Do enough of the boot stub to produce an EXE header and enter DPMI protected
mode.
This commit is contained in:
David Given
parent
3716d49cd9
commit
1e0961c679
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@ -12,141 +12,263 @@
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.sect .text
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.use16
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exe_header:
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.data2 0x5a4d ! magic number
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.data2 0 ! number of bytes in last loadable page
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.data2 exe_text_paras ! size of .exe, in pages
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.data2 0 ! number of relocation entries
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.data2 0 ! start of loadable area, in 16-byte paragraphs
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.data2 exe_ram_paras ! required RAM size, in 16-byte paragraphs
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.data2 0 ! maximum RAM siz, in 16-byte paragraphse
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.data2 0 ! initial SS, relative to program
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.data2 exe_stack ! initial SP
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.data2 0 ! checksum (ignored)
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.data2 exe_start ! initial IP
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.data2 0 ! initial CS, relative to program
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.data2 0 ! offset of relocation table
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.data2 0 ! overlay number
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dpmi_edi = 0x00
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dpmi_esi = 0x04
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dpmi_ebp = 0x08
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dpmi_ebx = 0x10
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dpmi_edx = 0x14
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dpmi_ecx = 0x18
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dpmi_eax = 0x1c
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dpmi_flags = 0x20
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dpmi_es = 0x22
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dpmi_ds = 0x24
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dpmi_fs = 0x26
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dpmi_gs = 0x28
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dpmi_ip = 0x2a
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dpmi_cs = 0x2c
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dpmi_sp = 0x2e
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dpmi_ss = 0x30
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dpmi_ps = 0x32 ! WORD: protected register segment
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dpmi_rs = 0x34 ! WORD: real register segment
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dpmi_psp = 0x36 ! WORD: PSP segment
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dpmi_switch = 0x38 ! DWORD: far pointer of pmode switch routine
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.seek 0x3c
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exe_start:
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! On entry, DS=ES=PSP. Make DS=CS, so we're running in tiny mode.
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push cs
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pop ds
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mov (dpmi_rs), ds
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mov (dpmi_psp), es
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! Initialise DPMI.
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mov ax, 0x1687
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int 0x2f
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or ax, ax
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jnz no_dpmi
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mov (dpmi_switch+0), di ! write back PMODE switch routine
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mov (dpmi_switch+2), es
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or si, si ! do we need a DPMI private area?
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jz 1f
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mov bx, si
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movb ah, 0x48
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int 0x21 ! allocate memory from DOS
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mov es, ax ! data area segment -> es
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1:
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! Switch to protected mode.
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mov ax, 1 ! 32-bit app
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callf (dpmi_switch)
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jc no_pmode
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mov (dpmi_edx), go_msg
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mov ax, (dpmi_rs)
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mov (dpmi_ds), ax
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mov (dpmi_eax+1), 9
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call int21
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mov ax, 0x4c00
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int 0x21
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! Simulate DOS interrupt bx.
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int21:
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mov bx, 0x21
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callint:
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xor ax, ax
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mov (dpmi_ss), ax ! zero stack: DPMI host allocates one.
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mov (dpmi_sp), ax
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push ds
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pop es
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mov di, ax
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mov ax, 0x300
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int 0x31 ! simulate DOS interrupt
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push cs
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pop ds
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ret
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no_pmode: ! Could not switch to protected mode.
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mov dx, no_pmode_msg
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jmp exit_with_error
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no_dpmi:
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mov dx, no_dpmi_msg
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! fall through
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! Displays the message in dx and exits.
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exit_with_error:
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movb ah, 9
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int 0x21 ! print $-terminated string
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mov ax, 0x4cff
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int 0x21 ! terminate with error code al
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.use32
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start_32bit:
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go_msg:
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.ascii "Go!$"
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no_pmode_msg:
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.ascii "Couldn't switch to protected mode$"
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no_dpmi_msg:
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.ascii "No DPMI$"
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exe_top:
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exe_stack = exe_top + 512
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exe_text_paras = [exe_top - exe_header + 511] / 512
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exe_ram_paras = [exe_stack - exe_top + 15] / 16
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#define STACK_BUFFER 128 /* number of bytes to leave for stack */
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begtext:
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! Make sure we are running under MS-DOS 2 or above.
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!
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! While at it, also remember the actual DOS version, so that we know
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! whether DOS gives us the program's name in the environment
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! segment. (DOS 3+ does; DOS 2.x does not.)
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movb ah, 0x30
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int 0x21
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cbw
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cmpb al, 2
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xchg bp, ax
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jnc ok_sys
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! Make sure we are running under MS-DOS 2 or above.
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!
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! While at it, also remember the actual DOS version, so that we know
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! whether DOS gives us the program's name in the environment
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! segment. (DOS 3+ does; DOS 2.x does not.)
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movb ah, 0x30
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int 0x21
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cbw
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cmpb al, 2
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xchg bp, ax
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jnc ok_sys
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mov dx, bad_sys_msg
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mov dx, bad_sys_msg
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dos_msg:
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movb ah, 9
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int 0x21
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ret
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ret
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ok_sys:
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! Resize the program's memory control block (MCB) to cover only the
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! program's near code and data space. Use the starting sp value as
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! a guide to how much memory we can grab. Abort on any failure.
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!
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! As a side effect, this also frees up any memory allocated to our
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! program beyond 64 KiB. (The freed memory can possibly be used by
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! e.g. child processes, in the future.)
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!
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! Also check that we have some space between the BSS end and the
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! starting sp.
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cmp sp, endbss+STACK_BUFFER
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jb no_room
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! Resize the program's memory control block (MCB) to cover only the
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! program's near code and data space. Use the starting sp value as
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! a guide to how much memory we can grab. Abort on any failure.
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!
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! As a side effect, this also frees up any memory allocated to our
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! program beyond 64 KiB. (The freed memory can possibly be used by
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! e.g. child processes, in the future.)
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!
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! Also check that we have some space between the BSS end and the
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! starting sp.
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cmp sp, endbss+STACK_BUFFER
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jb no_room
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movb ah, 0x4a
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mov bx, sp
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movb cl, 4
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shr bx, cl
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inc bx
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int 0x21
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jc no_room
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movb ah, 0x4a
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mov bx, sp
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movb cl, 4
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shr bx, cl
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inc bx
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int 0x21
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jc no_room
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! Clear BSS.
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mov di, begbss
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mov cx, endbss+1
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sub cx, di
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shr cx, 1
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xor ax, ax
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cld
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rep stosw
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! Clear BSS.
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mov di, begbss
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mov cx, endbss+1
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sub cx, di
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shr cx, 1
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xor ax, ax
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cld
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rep stosw
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! Get the size of the environment variables plus (if present) the
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! program name. Also count the number of environment variables.
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xor di, di
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mov es, 0x002C(di)
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! ax = 0 from above
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cwd ! dx = count of env. vars.
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! cx = 0 from above
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dec cx ! cx = max. str. bytes to scan
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scasb ! handle special case of empty env.
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jz is_empty_env
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! Get the size of the environment variables plus (if present) the
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! program name. Also count the number of environment variables.
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xor di, di
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mov es, 0x002C(di)
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! ax = 0 from above
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cwd ! dx = count of env. vars.
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! cx = 0 from above
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dec cx ! cx = max. str. bytes to scan
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scasb ! handle special case of empty env.
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jz is_empty_env
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size_env:
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inc dx
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repnz scasb
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scasb
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jnz size_env
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inc dx
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repnz scasb
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scasb
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jnz size_env
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is_empty_env:
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cmp bp, 2
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jz no_argv0
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scasw
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repnz scasb
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cmp bp, 2
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jz no_argv0
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scasw
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repnz scasb
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no_argv0:
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! Copy out the environment variables and (possibly) program name
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! onto the stack.
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mov si, di
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dec si
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std
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! Copy out the environment variables and (possibly) program name
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! onto the stack.
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mov si, di
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dec si
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std
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copy_env:
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and si, -2
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eseg lodsw
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push ax
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jnz copy_env
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mov cx, sp
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and si, -2
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eseg lodsw
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push ax
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jnz copy_env
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mov cx, sp
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! Reset DF and es properly.
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cld
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push ss
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pop es
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! Reset DF and es properly.
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cld
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push ss
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pop es
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! Reserve space for argc and the argv and envp pointers on the
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! stack. These will be passed to __m_a_i_n later.
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sub sp, 6
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mov ax, sp
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! Reserve space for argc and the argv and envp pointers on the
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! stack. These will be passed to __m_a_i_n later.
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sub sp, 6
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mov ax, sp
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! Build up argc, argv[], and envp[].
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push ax ! output buffer for argc, argv, envp
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push bp ! MS-DOS version
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push cx ! env. string data
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push dx ! count of env. vars.
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mov ax, 0x0080
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push ax ! raw command line
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call __sys_initmain
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add sp, 10
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! Build up argc, argv[], and envp[].
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push ax ! output buffer for argc, argv, envp
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push bp ! MS-DOS version
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push cx ! env. string data
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push dx ! count of env. vars.
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mov ax, 0x0080
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push ax ! raw command line
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call __sys_initmain
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add sp, 10
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! Bail out if something went wrong.
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test ax, ax
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jnz no_room
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! Bail out if something went wrong.
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test ax, ax
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jnz no_room
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! argc, argv, and envp are now at the stack top. Now go.
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call __m_a_i_n
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add sp, 6
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push ax
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call _exit
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! argc, argv, and envp are now at the stack top. Now go.
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call __m_a_i_n
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add sp, 6
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push ax
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call _exit
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no_room:
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mov dx, no_room_msg
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call dos_msg
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movb al, -1
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jmp al_exit
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mov dx, no_room_msg
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call dos_msg
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movb al, -1
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jmp al_exit
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! Exit.
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! Exit.
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.define __exit
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.extern __exit
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.define EXIT
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.extern EXIT
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__exit:
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EXIT:
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pop bx
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pop ax
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pop bx
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pop ax
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al_exit:
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movb ah, 0x4c
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int 0x21
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movb ah, 0x4c
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int 0x21
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! Define symbols at the beginning of our various segments, so that we can find
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! them. (Except .text, which has already been done.)
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@ -168,3 +290,6 @@ no_room_msg: .ascii 'No room$'
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.comm .trppc, 4
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.comm .ignmask, 4
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.comm _errno, 4
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! vim: ts=4 sw=4 et ft=asm
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