EXEC.ASM

SUBTTL $exec - load/go a program
PAGE
;
; Assembler usage:
;           LDS     DX, name
;           LES     BX, blk
;           MOV     AH, Exec
;           MOV     AL, func
;           INT     int_command
;
;       AL  Function
;       --  --------
;        0  Load and execute the program.
;        1  Load, create  the  program  header  but  do  not
;           begin execution.
;        3  Load overlay. No header created.
;
;           AL = 0 -> load/execute program
;
;           +---------------------------+
;           | WORD segment address of   |
;           | environment.              |
;           +---------------------------+
;           | DWORD pointer to ASCIZ    |
;           | command line at 80h       |
;           +---------------------------+
;           | DWORD pointer to default  |
;           | FCB to be passed at 5Ch   |
;           +---------------------------+
;           | DWORD pointer to default  |
;           | FCB to be passed at 6Ch   |
;           +---------------------------+
;
;           AL = 1 -> load program
;
;           +---------------------------+
;           | WORD segment address of   |
;           | environment.              |
;           +---------------------------+
;           | DWORD pointer to ASCIZ    |
;           | command line at 80h       |
;           +---------------------------+
;           | DWORD pointer to default  |
;           | FCB to be passed at 5Ch   |
;           +---------------------------+
;           | DWORD pointer to default  |
;           | FCB to be passed at 6Ch   |
;           +---------------------------+
;           | DWORD returned value of   |
;           | CS:IP                     |
;           +---------------------------+
;           | DWORD returned value of   |
;           | SS:IP                     |
;           +---------------------------+
;
;           AL = 3 -> load overlay
;
;           +---------------------------+
;           | WORD segment address where|
;           | file will be loaded.      |
;           +---------------------------+
;           | WORD relocation factor to |
;           | be applied to the image.  |
;           +---------------------------+
;
; Returns:
;           AX = exec_invalid_function
;              = exec_bad_format
;              = exec_bad_environment
;              = exec_not_enough_memory
;              = exec_file_not_found
;

IF IBM
ZEXEC_DATA  SEGMENT PUBLIC BYTE
ZERO =   $
ENDIF

exec_blk            DD  ?
exec_func           DB  ?
exec_fh             DW  ?
exec_rel_fac        DW  ?
exec_res_len_para   DW  ?
exec_init_IP        DW  ?
exec_init_CS        DW  ?
exec_init_SP        DW  ?
exec_init_SS        DW  ?
exec_environ        DW  ?
exec_size           DW  ?
exec_load_block     DW  ?

exec_load_high      DB  ?

exec_internal_buffer    EQU $
exec_signature      DW  ?               ; must contain 4D5A  (yay zibo!)
exec_len_mod_512    DW  ?               ; low 9 bits of length
exec_pages          DW  ?               ; number of 512b pages in file
exec_rle_count      DW  ?               ; count of reloc entries
exec_par_dir        DW  ?               ; number of paragraphs before image
exec_min_BSS        DW  ?               ; minimum number of para of BSS
exec_max_BSS        DW  ?               ; max number of para of BSS
exec_SS             DW  ?               ; stack of image
exec_SP             DW  ?               ; SP of image
exec_chksum         DW  ?               ; checksum  of file (ignored)
exec_IP             DW  ?               ; IP of entry
exec_CS             DW  ?               ; CS of entry
exec_rle_table      DW  ?               ; byte offset of reloc table
exec_iov            DW  ?               ; overlay number (0 for root)
exec_dma            DW  ?
exec_internal_buffer_size   EQU $-exec_internal_buffer

IF IBM
exec_ctrlc          DB  ?               ; state of users ctrlc flag
Exec_low_seg        DW  ?
CurrentPDB          DW  ?
NUMIO               DB  ?
ZEXECDATASIZ    =       $-ZERO
ZEXECDATAEND    LABEL   BYTE
        PUBLIC  ZEXECDATAEND
ZEXEC_DATA  ENDS
ZEXEC_CODE  SEGMENT PUBLIC PARA
        PUBLIC  $EXEC
ZERO =   $
        procedure   $EXEC,FAR
        ASSUME  CS:EGROUP,SS:RESGROUP,ES:NOTHING,DS:NOTHING
ENDIF
IF NOT IBM
        procedure   $Exec,NEAR
        ASSUME  DS:NOTHING, ES:NOTHING
ENDIF
;
; validate function
;

IF IBM
        PUSH    CS
        POP     DS
        ASSUME  DS:EGROUP

        MOV     AX,(Set_Ctrl_C_Trapping SHL 8) + 0      ; Save current ctrl-c
        INT     int_command
        MOV     exec_ctrlc,DL
        XOR     DX,DX
        MOV     AX,(Set_Ctrl_C_Trapping SHL 8) + 1      ; Turn it off!
        INT     int_command

        MOV     AH,Get_current_PDB
        INT     int_command
        MOV     [CurrentPDB],BX
;
; set up user return stack info
;
        MOV     ES,BX
        LES     BX,DWORD PTR [user_sp]
        MOV     WORD PTR ES:[PDB_user_stack+2],ES
        MOV     WORD PTR ES:[PDB_user_stack],BX

        MOV     AH,Get_Default_Drive
        INT     int_command
        MOV     DL,AL
        MOV     AH,Set_default_drive
        INT     int_command
        MOV     [NUMIO],AL
;
; determine lowest seg address for overwrite problem (round DOWN)
;
        MOV     CL,4
        MOV     AX,OFFSET ZEXEC_CODE:exec_check
        SHR     AX,CL
        PUSH    CS
        POP     BX
        ADD     AX,BX
        MOV     [exec_low_seg],AX

        CALL    get_user_stack
        ASSUME  DS:NOTHING
        MOV     AX,[SI.user_AX]
        MOV     BX,[SI.user_BX]
        MOV     DX,[SI.user_DX]
        MOV     ES,[SI.user_ES]
        MOV     DS,[SI.user_DS]
ENDIF

        CMP     AL,3                    ; only 0, 1 or 3 are allowed
        JNA     exec_check_2

exec_bad_fun:
        error   error_invalid_function

exec_ret_err:
        transfer    SYS_RET_ERR

exec_check_2:
        CMP     AL,2
        JZ      exec_bad_fun

        MOV     WORD PTR [exec_blk],BX  ; stash args
        MOV     WORD PTR [exec_blk+2],ES
        MOV     BYTE PTR [exec_func],AL
        MOV     BYTE PTR [exec_load_high],0
IF IBM
        MOV     AX,(OPEN SHL 8) + 0
        INT     int_command
ENDIF
IF NOT IBM
        XOR     AL,AL                   ; open for reading
        invoke  $OPEN                   ; is the file there?
ENDIF
        JC      exec_ret_err
        MOV     [exec_fh],AX
        MOV     BX,AX
IF IBM
        MOV     AX,(ioctl SHL 8)        ; get device information
        INT     int_command
ENDIF
IF NOT IBM
        XOR     AL,AL
        invoke  $IOCTL
ENDIF
        TEST    DL,devid_ISDEV
        JZ      exec_check_environ
        MOV     AL,exec_file_not_found
        transfer    SYS_RET_ERR

exec_check_environ:
        MOV     [exec_load_block],0

        TEST    BYTE PTR [exec_func],exec_func_overlay   ; overlays... no environment
        JNZ     exec_read_header
        LDS     SI,DWORD PTR [exec_blk] ; get block
        MOV     AX,[SI].Exec1_environ   ; address of environ
        OR      AX,AX
        JNZ     exec_scan_env
        MOV     DS,[CurrentPDB]
        MOV     AX,DS:[PDB_environ]
        MOV     [exec_environ],AX
        OR      AX,AX
        JZ      exec_read_header

exec_scan_env:
        CLD
        MOV     ES,AX
        XOR     DI,DI
        MOV     CX,07FFFh               ; at most 32k of environment
        XOR     AL,AL

exec_get_environ_len:
        REPNZ   SCASB                   ; find that nul byte
        JZ      exec_check              ; CX is out... bad environment
        MOV     AL,exec_bad_environment
        JMP     exec_bomb

exec_check:
        SCASB                           ; is there another nul byte?
        JNZ     exec_get_environ_len    ; no, scan some more
        PUSH    DI
        MOV     BX,DI                   ; AX <- length of environment
        ADD     BX,0Fh
        MOV     CL,4
        SHR     BX,CL                   ; number of paragraphs needed
        PUSH    ES
IF IBM
        MOV     AH,ALLOC
        INT     int_command
ENDIF
IF NOT IBM
        invoke  $ALLOC                  ; can we get the space?
ENDIF
        POP     DS
        POP     CX
        JNC     exec_save_environ
        JMP     exec_no_mem             ; nope... cry and sob

exec_save_environ:
        MOV     ES,AX
        MOV     [exec_environ],AX       ; save him for a rainy day
IF IBM
        PUSH    CX
        MOV     CX,ES
        ADD     CX,BX
        CMP     BX,[exec_low_seg]
        POP     CX
        JA      exec_no_mem
ENDIF
        XOR     SI,SI
        XOR     DI,DI
        REP     MOVSB                   ; copy the environment

exec_read_header:
;
; We read in the program header into the above data area and determine
; where in this memory the image will be located.
;
IF IBM
        PUSH    CS
        POP     DS                      ; and put it in DS:DX
        ASSUME  DS:EGROUP
ENDIF
IF NOT IBM
        PUSH    SS
        POP     DS                      ; and put it in DS:DX
        ASSUME  DS:DOSGROUP
ENDIF
        MOV     CX,exec_internal_buffer_size; header size
        MOV     BX,[exec_fh]            ; from the handle
IF IBM
        MOV     DX,OFFSET EGROUP:exec_signature
ENDIF
IF NOT IBM
        MOV     DX,OFFSET DOSGROUP:exec_signature
ENDIF
        PUSH    ES
        PUSH    DS
        CALL    exec_dealloc
IF IBM
        MOV     AH,READ
        INT     int_command
ENDIF
IF NOT IBM
        invoke  $READ
ENDIF
        CALL    exec_alloc
        POP     DS
        POP     ES
        JC      exec_bad_file
        CMP     AX,exec_internal_buffer_size; did we read the right number?
        JNZ     exec_com_filej          ; yep... continue
        CMP     [exec_max_BSS],0
        JNZ     exec_check_sig
        MOV     [exec_load_high],-1
exec_check_sig:
        MOV     AX,[exec_signature]
        CMP     AX,exe_valid_signature  ; zibo arises!
        JZ      exec_save_start         ; assume com file if no signature
        CMP     AX,exe_valid_old_signature  ; zibo arises!
        JZ      exec_save_start         ; assume com file if no signature

exec_com_filej:
        JMP     exec_com_file

;
; We have the program header... determine memory requirements
;
exec_save_start:
        MOV     AX,[exec_pages]         ; get 512-byte pages
        MOV     CL,5                    ; convert to paragraphs
        SHL     AX,CL
        SUB     AX,[exec_par_dir]       ; AX = size in paragraphs
        MOV     [exec_res_len_para],AX

;
; Do we need to allocate memory?  Yes if function is not load-overlay
;
        TEST    BYTE PTR [exec_func],exec_func_overlay
        JZ      exec_allocate           ; allocation of space
;
; get load address from block
;
        LES     DI,DWORD PTR [exec_blk]
        MOV     AX,ES:[DI].exec3_load_addr
        MOV     [exec_dma],AX
        MOV     AX,ES:[DI].exec3_reloc_fac
        MOV     [exec_rel_fac],AX
IF IBM
        JMP     exec_find_res
ENDIF
IF NOT IBM
        JMP     SHORT exec_find_res
ENDIF

exec_no_mem:
        MOV     AL,exec_not_enough_memory
        JMP     SHORT exec_bomb             ; AX should be set by $ALLOC

exec_bad_file:
        MOV     AL,exec_bad_format

exec_bomb:
        ASSUME  DS:NOTHING,ES:NOTHING
        PUSH    AX
        MOV     BX,[exec_fh]
        CALL    exec_dealloc
IF IBM
        MOV     AH,CLOSE
        INT     int_command
ENDIF
IF NOT IBM
        invoke  $CLOSE
ENDIF
        POP     AX
        transfer    SYS_RET_ERR

exec_allocate:
IF IBM
        ASSUME  DS:EGROUP
ENDIF
IF NOT IBM
        ASSUME  DS:DOSGROUP
ENDIF
        PUSH    AX
        MOV     BX,0FFFFh               ; see how much room in arena
        PUSH    DS
IF IBM
        MOV     AH,ALLOC
        INT     int_command
ENDIF
IF NOT IBM
        invoke  $ALLOC                  ; should have carry set and BX has max
ENDIF
        POP     DS
        POP     AX
        ADD     AX,10h                  ; room for header
        CMP     BX,11h                  ; enough room for a header
        JB      exec_no_mem
        CMP     AX,BX                   ; is there enough for bare image?
        JA      exec_no_mem
        CMP     [exec_load_high],0      ; if load high, use max
        JNZ     exec_BX_max             ; use max
        ADD     AX,[exec_min_BSS]       ; go for min allocation
        JC      exec_no_mem             ; oops! carry
        CMP     AX,BX                   ; enough space?
        JA      exec_no_mem             ; nope...
        SUB     AX,[exec_min_BSS]
        ADD     AX,[exec_max_BSS]       ; go for the MAX
        JC      exec_BX_max
        CMP     AX,BX
        JBE     exec_got_block

exec_BX_max:
        MOV     AX,BX

exec_got_block:
        PUSH    DS
        MOV     BX,AX
        MOV     [exec_size],BX
IF IBM
        MOV     AH,ALLOC
        INT     int_command
ENDIF
IF NOT IBM
        invoke  $ALLOC                  ; get the space
ENDIF
        POP     DS
        JC      exec_no_mem
        MOV     [exec_load_block],AX
        ADD     AX,10h
        CMP     [exec_load_high],0
        JZ      exec_use_ax             ; use ax for load info
        ADD     AX,[exec_size]          ; go to end
        SUB     AX,[exec_res_len_para]  ; drop off header
        SUB     AX,10h                  ; drop off pdb
exec_use_ax:
        MOV     [exec_rel_fac],AX       ; new segment
        MOV     [exec_dma],AX           ; beginning of dma
IF IBM
        CMP     AX,[exec_low_seg]       ; below loader
        JA      exec_no_mem_try
        ADD     AX,[exec_res_len_para]  ; go to end
        CMP     Ax,[exec_low_seg]       ; above loader
        JBE     exec_find_res
exec_try_high:
        CMP     [exec_load_high],0
        JZ      exec_no_memj1
exec_try_just_below:
        MOV     DX,AX
        SUB     DX,[exec_size]          ; get beginning
        ADD     DX,[exec_res_len_para]  ; no space
        CMP     DX,[exec_low_seg]       ; room there?
        JA      exec_no_memj1
        MOV     AX,[exec_low_seg]
        SUB     AX,[exec_res_len_para]
        JMP     exec_use_ax
exec_no_mem_try:
        MOV     DX,CS
        ADD     DX,(zexecdatasiz+zexeccodesize+15)/16
        CMP     AX,DX
        JAE     exec_try_high
        JMP     exec_try_just_below
exec_no_memj1:
        JMP     exec_no_mem
ENDIF

;
; Determine the location in the file of the beginning of the resident
;
exec_find_res:
        MOV     DX,[exec_par_dir]
        PUSH    DX
        MOV     CL,4
        SHL     DX,CL                   ; low word of location
        POP     AX
        MOV     CL,12
        SHR     AX,CL                   ; high word of location
        MOV     CX,AX                   ; CX <- high

;
; Read in the resident image (first, seek to it)
;
        MOV     BX,[exec_fh]
        PUSH    DS
IF IBM
        MOV     AX,(LSEEK SHL 8) + 0
        INT     int_command
ENDIF
IF NOT IBM
        XOR     AL,AL
        invoke  $LSEEK                  ; seek to resident
ENDIF
        POP     DS

exec_big_read:                          ; Read resident into memory
        MOV     BX,[exec_res_len_para]
        CMP     BX,1000h                ; too many bytes to read?
        JB      exec_read_ok
        MOV     BX,0FE0h                ; max in one chunk FE00 bytes

exec_read_ok:
        SUB     [exec_res_len_para],BX  ; we read (soon) this many
        PUSH    BX
        MOV     CL,4
        SHL     BX,CL                   ; get count in bytes from paras
        MOV     CX,BX                   ; count in correct register
        MOV     BX,[exec_fh]            ; handle in correct register
        PUSH    DS
        MOV     DS,[exec_dma]           ; Set up read buffer
        ASSUME  DS:NOTHING
        XOR     DX,DX
        PUSH    CX                      ; save our count
        CALL    exec_dealloc
IF IBM
        MOV     AH,READ
        INT     int_command
ENDIF
IF NOT IBM
        invoke  $READ                   ; WOMP!
ENDIF
        CALL    exec_alloc
        POP     CX                      ; get old count to verify
        POP     DS
IF IBM
        ASSUME  DS:EGROUP
ENDIF
IF NOT IBM
        ASSUME  DS:DOSGROUP
ENDIF
        CMP     CX,AX                   ; did we read enough?
        POP     BX                      ; get paragraph count back
        JNZ     exec_do_reloc           ; and do reloc if no more to read
;
; We've read in CX bytes... bump DTA location
;

        ADD     [exec_dma],BX           ; bump dma address
        CMP     [exec_res_len_para],0
        JNZ     exec_big_read

;
; The image has now been read in.  We must perform relocation to
; the current location.
;

exec_do_reloc:
        MOV     CX,[exec_rel_fac]
        MOV     AX,[exec_SS]            ; get initial SS
        ADD     AX,CX                   ; and relocate him
        MOV     [exec_init_SS],AX

        MOV     AX,[exec_SP]            ; initial SP
        MOV     [exec_init_SP],AX

        LES     AX,DWORD PTR [exec_IP]
        MOV     [exec_init_IP],AX
        MOV     AX,ES
        ADD     AX,CX                   ; relocated...
        MOV     [exec_init_CS],AX

        XOR     CX,CX
        MOV     DX,[exec_rle_table]
        MOV     BX,[exec_fh]
        PUSH    DS
IF IBM
        MOV     AX,(LSEEK SHL 8) + 0
        INT     int_command
ENDIF
IF NOT IBM
        XOR     AX,AX
        invoke  $LSEEK
ENDIF
        POP     DS

        JNC     exec_get_entries
exec_bad_filej:
        JMP     exec_bad_file

exec_get_entries:
        MOV     DX,[exec_rle_count]     ; Number of entries left

exec_read_reloc:
        ASSUME  DS:NOTHING
        PUSH    DX
IF IBM
        MOV     DX,OFFSET EGROUP:exec_signature
ENDIF
IF NOT IBM
        MOV     DX,OFFSET DOSGROUP:exec_signature
ENDIF
        MOV     CX,((exec_internal_buffer_size)/4)*4
        MOV     BX,[exec_fh]
        PUSH    DS
        CALL    exec_dealloc
IF IBM
        MOV     AH,READ
        INT     int_command
ENDIF
IF NOT IBM
        invoke  $READ
ENDIF
        CALL    exec_alloc
        POP     ES
        POP     DX
        JC      exec_bad_filej
        MOV     CX,(exec_internal_buffer_size)/4
IF IBM
        MOV     DI,OFFSET EGROUP:exec_signature   ; Pointer to byte location in header
ENDIF
IF NOT IBM
        MOV     DI,OFFSET DOSGROUP:exec_signature   ; Pointer to byte location in header
ENDIF
;
; Relocate a single address
;
        MOV     SI,[exec_rel_fac]

exec_reloc_one:
        CMP     DX,0                    ; Any more entries?
        JNE     exec_get_addr
        JMP     Exec_set_PDB

exec_get_addr:
        LDS     BX,DWORD PTR ES:[DI]    ; Get ra/sa of entry
        MOV     AX,DS                   ; Relocate address of item
        ADD     AX,SI
        MOV     DS,AX
        MOV     AX,WORD PTR DS:[BX]     ; Relocate item
        ADD     AX,SI
        MOV     WORD PTR DS:[BX],AX
        ADD     DI,4
        DEC     DX
        LOOP    exec_reloc_one              ; End of internal buffer?

;
; We've exhausted a single buffer's worth.  Read in the next piece
; of the relocation table.
;

        PUSH    ES
        POP     DS
        JMP     exec_read_reloc

exec_no_memj:
        JMP     exec_no_mem

;
; we have a .COM file.  First, determine if we are merely loading an overlay.
;
exec_com_file:
        TEST    BYTE PTR [exec_func],exec_func_overlay
        JZ      exec_alloc_com_file
        LDS     SI,DWORD PTR [exec_blk]           ; get arg block
        LODSW                           ; get load address
        MOV     [exec_dma],AX
        JMP     SHORT exec_64k          ; read it all!

; We must allocate the max possible size block (ick!)  and set up
; CS=DS=ES=SS=PDB pointer, IP=100, SP=max size of block.
;
exec_alloc_com_file:
        MOV     BX,0FFFFh
IF IBM
        MOV     AH,ALLOC
        INT     int_command
ENDIF
IF NOT IBM
        invoke  $ALLOC                  ; largest piece available as error
ENDIF
        OR      BX,BX
        JZ      exec_no_memj
        MOV     [exec_size],BX          ; save size of allocation block
IF IBM
        MOV     AH,ALLOC
        INT     int_command
ENDIF
IF NOT IBM
        PUSH    BX
        invoke  $ALLOC                  ; largest piece available as error
        POP     BX                      ; get size of block...
ENDIF
        MOV     [exec_load_block],AX
        ADD     AX,10h                  ; increment for header
        MOV     [exec_dma],AX
        SUB     BX,10h                  ; remember header
IF IBM
;
; need to read up to exec_low_seg (at most)
;
        MOV     CX,[exec_low_seg]
        CMP     AX,CX                   ; is base of allocation above spot
        JA      exec_check_64k
        SUB     CX,AX
        CMP     CX,BX
        JA      exec_check_64k
        MOV     BX,CX

exec_check_64k:
ENDIF
        CMP     BX,1000h                ; 64k or more?
        JAE     exec_64k                ; yes, read only 64k
        MOV     AX,BX                   ; convert size to bytes
        MOV     CL,4
        SHL     AX,CL
        JMP     SHORT exec_read_com

exec_64k:
        MOV     AX,0FFFFh               ; 64k-1 bytes

exec_read_com:
        PUSH    AX                      ; save number to read
        MOV     BX,[exec_fh]            ; of com file
        XOR     CX,CX                   ; but seek to 0:0
        MOV     DX,CX
IF IBM
        MOV     AX,(LSEEK SHL 8) + 0
        INT     int_command
ENDIF
IF NOT IBM
        XOR     AX,AX                   ; seek relative to beginning
        invoke  $LSEEK                  ; back to beginning of file
ENDIF
        MOV     BX,[exec_fh]
        POP     CX                      ; number to read
        MOV     DS,[exec_dma]
        XOR     DX,DX
        PUSH    CX
        CALL    exec_dealloc
IF IBM
        MOV     AH,READ
        INT     int_command
ENDIF
IF NOT IBM
        invoke  $READ                   ; read in com file
ENDIF
        CALL    exec_alloc
        POP     SI                      ; get number of bytes to read
        CMP     AX,SI                   ; did we read them all?
IF IBM
        JNZ     exec_skip               ; exactly the wrong number... no memory
        JMP     exec_no_mem
exec_skip:
ENDIF
IF NOT IBM
        JZ      exec_no_memj            ; exactly the wrong number... no memory
ENDIF
        TEST    BYTE PTR [exec_func],exec_func_overlay
        JNZ     exec_set_PDB            ; no starto, chumo!
        MOV     AX,[exec_DMA]
        SUB     AX,10h
        MOV     [exec_init_CS],AX
        MOV     [exec_init_IP],100h     ; initial IP is 100
        ; SI is at most FFFFh
        DEC     SI                      ; make room for stack
        ; SI is at most FFFEh, room for a 0!
        MOV     [exec_init_SP],SI       ; max value for read is also SP!
        MOV     [exec_init_SS],AX
        MOV     DS,AX
        MOV     WORD PTR DS:[SI],0      ; 0 for return

exec_set_PDB:
        MOV     BX,[exec_fh]            ; we are finished with the file.
        CALL    exec_dealloc
IF IBM
        MOV     AH,CLOSE
        INT     int_command
ENDIF
IF NOT IBM
        invoke  $CLOSE                  ; release the jfn
ENDIF
        CALL    exec_alloc
        TEST    BYTE PTR [exec_func],exec_func_overlay
        JZ      exec_build_header
        transfer    SYS_RET_OK          ; overlay load -> done

exec_build_header:
        MOV     DX,[exec_load_block]
;
; assign the space to the process
;

        MOV     SI,arena_owner          ; pointer to owner field

        MOV     AX,[exec_environ]       ; get environ pointer
        OR      AX,AX
        JZ      NO_OWNER                ; no environment
        DEC     AX                      ; point to header
        MOV     DS,AX
        MOV     DS:[SI],DX              ; assign ownership
NO_OWNER:
        MOV     AX,[exec_load_block]    ; get load block pointer
        DEC     AX
        MOV     DS,AX                   ; point to header
        MOV     DS:[SI],DX              ; assign ownership

        PUSH    DX
IF IBM
        MOV     AH,DUP_PDB
        INT     int_command
        MOV     ES,DX
        MOV     [CurrentPDB],DX
ENDIF
IF NOT IBM
        MOV     BYTE PTR [CreatePDB], 0FFH  ; indicate a new process
        invoke  $Dup_PDB                    ; ES is now PDB
ENDIF
        POP     DX
        PUSH    [exec_environ]
        POP     ES:[PDB_environ]
        MOV     SI,[exec_size]
        ADD     SI,DX
        MOV     ES:[PDB_block_len],SI
;
; set up proper command line stuff
;
        LDS     SI,DWORD PTR [exec_blk]           ; get the block
        PUSH    DS                      ; save its location
        PUSH    SI
        LDS     SI,DS:[SI.exec0_5C_FCB] ; get the 5c fcb
        MOV     CX,12                   ; copy drive, name and ext
        PUSH    CX
        MOV     DI,5Ch
        MOV     BL,DS:[SI]
        REP     MOVSB
        XOR     AX,AX                   ; zero extent, etc for CPM
        STOSW
        STOSW
        POP     CX
        POP     SI                      ; get block
        POP     DS
        PUSH    DS                      ; save (again)
        PUSH    SI
        LDS     SI,DS:[SI.exec0_6C_FCB] ; get 6C FCB
        MOV     DI,6Ch                  ; do same as above
        MOV     BH,DS:[SI]
        REP     MOVSB
        STOSW
        STOSW
        POP     SI                      ; get block (last time)
        POP     DS
        LDS     SI,DS:[SI.exec0_com_line]   ; command line
        MOV     CX,80h
        MOV     DI,CX
        REP     MOVSB                   ; Wham!

;
; Process BX into default AX (validity of drive specs on args)
;
        DEC     CL                      ; get 0FFh in CX
        CMP     BH,[NUMIO]
        JBE     exec_BH_good
        MOV     BH,CL
        JMP     SHORT exec_BL
exec_BH_good:
        XOR     BH,BH
exec_BL:
        CMP     BL,[NUMIO]
        JBE     exec_BL_good
        MOV     BL,CL
        JMP     SHORT exec_set_return
exec_BL_good:
        XOR     BL,BL
exec_set_return:
        invoke  get_user_stack          ; get his return address
        PUSH    [SI.user_CS]            ; suck out the CS and IP
        PUSH    [SI.user_IP]
        PUSH    [SI.user_CS]            ; suck out the CS and IP
        PUSH    [SI.user_IP]
        POP     WORD PTR ES:[PDB_Exit]
        POP     WORD PTR ES:[PDB_Exit+2]
        XOR     AX,AX
        MOV     DS,AX
        POP     DS:[addr_int_terminate] ; save them where we can get them later
        POP     DS:[addr_int_terminate+2]   ; when the child exits.
IF NOT IBM
        MOV     WORD PTR [DMAADD],80h
        MOV     DS,[CurrentPDB]
        MOV     WORD PTR [DMAADD+2],DS
ENDIF
IF IBM
        PUSH    DX
        PUSH    DS
        MOV     DS,[CurrentPDB]
        MOV     DX,80h
        MOV     AH,SET_DMA
        INT     int_command
        POP     DS
        POP     DX
ENDIF
        TEST    BYTE PTR [exec_func],exec_func_no_execute
        JZ      exec_go

        LDS     SI,DWORD PTR [exec_init_SP] ; get stack
        LES     DI,DWORD PTR [exec_blk]           ; and block for return
        MOV     ES:[DI].exec1_SS,DS     ; return SS

        DEC     SI                      ; 'push' default AX
        DEC     SI
        MOV     DS:[SI],BX              ; save default AX reg
        MOV     ES:[DI].exec1_SP,SI     ; return 'SP'

        LDS     AX,DWORD PTR [exec_init_IP]
        MOV     ES:[DI].exec1_CS,DS     ; initial entry stuff

        MOV     ES:[DI].exec1_IP,AX
        transfer    SYS_RET_OK

exec_go:
IF IBM
        CALL    restore_ctrlc               ; restore value of ctrl-c checker
ENDIF
        LDS     SI,DWORD PTR [exec_init_IP] ; get entry point
        CLI
IF NOT IBM
        MOV     BYTE PTR INDOS,0
ENDIF
        MOV     SS,[exec_init_SS]       ; set up user's stack
        ASSUME  SS:NOTHING
        MOV     SP,[exec_init_SP]       ; and SP
        STI
        PUSH    DS                      ; fake long call to entry
        PUSH    SI
        MOV     ES,DX                   ; set up proper seg registers
        MOV     DS,DX
        MOV     AX,BX                   ; set up proper AX
        procedure   exec_long_ret,FAR
        RET
exec_long_ret   ENDP

$Exec   ENDP

        procedure   exec_dealloc,near
        ASSUME      DS:NOTHING,ES:NOTHING
        PUSH        BX
        MOV         BX,arena_owner_system
        CALL        exec_do_change_owner
        POP         BX
        return
exec_dealloc  ENDP

        procedure   exec_alloc,near
        PUSH        BX
        MOV         BX,[CurrentPDB]
        CALL        exec_do_change_owner
        POP         BX
        return
exec_alloc  ENDP

        procedure   exec_do_change_owner,NEAR
        PUSH    DS
        PUSH    AX
        MOV     AX,[exec_environ]
        OR      AX,AX
        JZ      exec_alloc_try_load
        DEC     AX
        MOV     DS,AX
        MOV     DS:[arena_owner],BX
exec_alloc_try_load:
        MOV     AX,[exec_load_block]
        OR      AX,AX
        JZ      exec_alloc_done
        DEC     AX
        MOV     DS,AX
        MOV     DS:[arena_owner],BX
exec_alloc_done:
        POP     AX
        POP     DS
        RET
exec_do_change_owner    ENDP

IF IBM
SYS_RET_ERR:
        CALL    get_user_stack
        PUSH    [SI.user_f]
        XOR     AH,AH
        MOV     [SI.user_AX],AX
        POPF
        STC
        JMP SYS_RET
SYS_RET_OK:
        CALL    get_user_stack
        PUSH    [SI.user_f]
        POPF
        CLC
SYS_RET:
        PUSHF
        CALL    restore_ctrlc
        POP     [SI.user_f]
        JMP     exec_long_ret

;
; get_user_stack returns the user's stack (and hence registers) in DS:SI
;
        procedure   get_user_stack,NEAR
        PUSH    SS
        POP     DS
        ASSUME  DS:RESGROUP
        LDS     SI,DWORD PTR [user_SP]
        RET
get_user_stack  ENDP
;
; restore value of the ctrl-c checker
;
        procedure    restore_ctrlc
        PUSH    AX
        PUSH    DX
        MOV     DL,CS:[exec_ctrlc]
        MOV     AX,(Set_Ctrl_C_Trapping SHL 8) + 1      ; Put it back
        INT     int_command
        POP     DX
        POP     AX
        RET
restore_ctrlc   ENDP

ZEXECCODESIZE   EQU     $-ZERO
ZEXECCODEEND    LABEL BYTE
        PUBLIC  ZEXECCODEEND
ZEXEC_CODE      ENDS
ENDIF