WebSVN – SvarDOS – Diff – /svarcom/trunk/rmod.asm


;
; rmod - resident module of the SvarCOM command interpreter
;
; Copyright (C) 2021 Mateusz Viste
; MIT license
;
; this is installed in memory by the transient part of SvarCOM. it has only
; two jobs: providing a resident buffer for command history, environment, etc
; and respawning COMMAND.COM whenever necessary.
 
CPU 8086
org 0h           ; this is meant to be executed without a PSP
 
section .text    ; all goes into code segment
 
                 ; offset
SIG1 dw 0x1983   ;  +0
SIG2 dw 0x1985   ;  +2
SIG3 dw 0x2017   ;  +4
SIG4 dw 0x2019   ;  +6
 
; environment segment - this is updated by SvarCOM at init time
ENVSEG   dw 0    ;  +8
 
; exit code of last application
LEXCODE  dw 0    ; +0Ah
 
; input buffer used for the "previous command" history
BUF000 db 128, 0 ; +0Ch
BUF064 db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"
BUF128 db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"
 
; offset of the COMSPEC variable in the environment block, 0 means "use
; boot drive". this value is patched by the transient part of COMMAND.COM
COMSPECPTR dw 0  ; +8Eh
 
; fallback COMSPEC string used if no COMPSEC is present in the environment
; drive. drive is patched by the transient part of COMMAND.COM
COMSPECBOOT db "@:\COMMAND.COM", 0 ; +90h
 
skipsig:         ; +9Fh
 
; set up CS=DS=SS and point SP to my private stack buffer
mov ax, cs
mov ds, ax
mov es, ax
mov ss, ax
mov sp, STACKPTR
 
; collect the exit code of previous application
mov ah, 0x4D
int 0x21
xor ah, ah          ; clear out termination status, I only want the exit code
mov [LEXCODE], ax
 
; preset the default COMSPEC pointer to ES:DX (ES is already set to DS)
mov dx, COMSPECBOOT
 
; do I have a valid COMSPEC?
or [COMSPECPTR], word 0
jz USEDEFAULTCOMSPEC
; set ES:DX to actual COMSPEC
mov es, [ENVSEG]
mov dx, [COMSPECPTR]
USEDEFAULTCOMSPEC:
 
; prepare the exec param block
mov ax, [ENVSEG]
mov [EXEC_PARAM_REC], ax
mov [EXEC_PARAM_REC+2], dx
mov [EXEC_PARAM_REC+4], es
 
; execute command.com
mov ax, 0x4B00         ; DOS 2+ - load & execute program
push es                ;
pop ds                 ;
;mov dx, COMSPEC       ; DS:DX  - ASCIZ program name (preset already)
push cs
pop es
mov bx, EXEC_PARAM_REC ; ES:BX  - parameter block pointer
int 0x21
 
; if all went well, jump back to start
jnc skipsig
 
; restore DS=CS
mov bx, cs
mov ds, bx
 
; update error string so it contains the error number
add al, '0'
mov [ERRLOAD + 4], al
 
; display error message
mov ah, 0x09
mov dx, ERRLOAD
int 0x21
 
; wait for keypress
mov ah, 0x08
int 0x21
 
; back to program start
jmp skipsig
 
; ExecParamRec used by INT 21h, AX=4b00 (load and execute program), 14 bytes:
;  offset  size  content
;     +0     2   segment of environment for child (0 = current)
;     +2     4   address of command line to place at PSP:0080
;     +6     4   address of an FCB to be placed at PSP:005c
;    +0Ah    4   address of an FCB to be placed at PSP:006c
EXEC_PARAM_REC db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
 
ERRLOAD db "ERR x, FAILED TO LOAD COMMAND.COM", 13, 10, '$'
 
; DOS int 21h functions that I use require at least 32 bytes of stack, here I
; allocate 64 bytes to be sure
STACKBUF db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"
STACKPTR db "xx"
 

Rev 366	Rev 398
1	`;`	1	`;`
2	`; rmod - resident module of the SvarCOM command interpreter`	2	`; rmod - resident module of the SvarCOM command interpreter`
3	`;`	3	`;`
4	`; Copyright (C) 2021 Mateusz Viste`	4	`; Copyright (C) 2021 Mateusz Viste`
5	`; MIT license`	5	`; MIT license`
6	`;`	6	`;`
7	`; this is installed in memory by the transient part of SvarCOM. it has only`	7	`; this is installed in memory by the transient part of SvarCOM. it has only`
8	`; two jobs: providing a resident buffer for command history, environment, etc`	8	`; two jobs: providing a resident buffer for command history, environment, etc`
9	`; and respawning COMMAND.COM whenever necessary.`	9	`; and respawning COMMAND.COM whenever necessary.`
10		10
11	`CPU 8086`	11	`CPU 8086`
12	`org 0h ; this is meant to be executed without a PSP`	12	`org 0h ; this is meant to be executed without a PSP`
13		13
14	`section .text ; all goes into code segment`	14	`section .text ; all goes into code segment`
15		15
16	`; offset`	16	`; offset`
17	`SIG1 dw 0x1983 ; +0`	17	`SIG1 dw 0x1983 ; +0`
18	`SIG2 dw 0x1985 ; +2`	18	`SIG2 dw 0x1985 ; +2`
19	`SIG3 dw 0x2017 ; +4`	19	`SIG3 dw 0x2017 ; +4`
20	`SIG4 dw 0x2019 ; +6`	20	`SIG4 dw 0x2019 ; +6`
21		21
22	`; environment segment - this is updated by SvarCOM at init time`	22	`; environment segment - this is updated by SvarCOM at init time`
23	`ENVSEG dw 0 ; +8`	23	`ENVSEG dw 0 ; +8`
24		24
25	`; exit code of last application`	25	`; exit code of last application`
26	`LEXCODE dw 0 ; +0Ah`	26	`LEXCODE dw 0 ; +0Ah`
27		27
28	`; input buffer used for the "previous command" history`	28	`; input buffer used for the "previous command" history`
29	`BUF000 db 128, 0 ; +0Ch`	29	`BUF000 db 128, 0 ; +0Ch`
30	`BUF064 db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"`	30	`BUF064 db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"`
31	`BUF128 db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"`	31	`BUF128 db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"`
32		32
33	`; offset of the COMSPEC variable in the environment block, 0 means "use`	33	`; offset of the COMSPEC variable in the environment block, 0 means "use`
34	`; boot drive". this value is patched by the transient part of COMMAND.COM`	34	`; boot drive". this value is patched by the transient part of COMMAND.COM`
35	`COMSPECPTR dw 0 ; +8Eh`	35	`COMSPECPTR dw 0 ; +8Eh`
36		36
37	`; fallback COMSPEC string used if no COMPSEC is present in the environment`	37	`; fallback COMSPEC string used if no COMPSEC is present in the environment`
38	`; drive. drive is patched by the transient part of COMMAND.COM`	38	`; drive. drive is patched by the transient part of COMMAND.COM`
39	`COMSPECBOOT db "@:\COMMAND.COM", 0 ; +90h`	39	`COMSPECBOOT db "@:\COMMAND.COM", 0 ; +90h`
40		40
41	`skipsig: ; +9Fh`	41	`skipsig: ; +9Fh`
42		42
43	`; set up CS=DS=SS and point SP to my private stack buffer`	43	`; set up CS=DS=SS and point SP to my private stack buffer`
44	`mov ax, cs`	44	`mov ax, cs`
45	`mov ds, ax`	45	`mov ds, ax`
46	`mov es, ax`	46	`mov es, ax`
47	`mov ss, ax`	47	`mov ss, ax`
48	`mov sp, STACKPTR`	48	`mov sp, STACKPTR`
49		49
50	`; collect the exit code of previous application`	50	`; collect the exit code of previous application`
51	`mov ah, 0x4D`	51	`mov ah, 0x4D`
52	`int 0x21`	52	`int 0x21`
53	`xor ah, ah ; clear out termination status, I only want the exit code`	53	`xor ah, ah ; clear out termination status, I only want the exit code`
54	`mov [LEXCODE], ax`	54	`mov [LEXCODE], ax`
55		55
56	`; preset the default COMSPEC pointer to ES:DX (ES is already set to DS)`	56	`; preset the default COMSPEC pointer to ES:DX (ES is already set to DS)`
57	`mov dx, COMSPECBOOT`	57	`mov dx, COMSPECBOOT`
58		58
59	`; do I have a valid COMSPEC?`	59	`; do I have a valid COMSPEC?`
60	`or [COMSPECPTR], word 0`	60	`or [COMSPECPTR], word 0`
61	`jz USEDEFAULTCOMSPEC`	61	`jz USEDEFAULTCOMSPEC`
62	`; set ES:DX to actual COMSPEC`	62	`; set ES:DX to actual COMSPEC`
63	`mov es, [ENVSEG]`	63	`mov es, [ENVSEG]`
64	`mov dx, [COMSPECPTR]`	64	`mov dx, [COMSPECPTR]`
65	`USEDEFAULTCOMSPEC:`	65	`USEDEFAULTCOMSPEC:`
66		66
67	`; prepare the exec param block`	67	`; prepare the exec param block`
68	`mov ax, [ENVSEG]`	68	`mov ax, [ENVSEG]`
69	`mov [EXEC_PARAM_REC], ax`	69	`mov [EXEC_PARAM_REC], ax`
70	`mov [EXEC_PARAM_REC+2], dx`	70	`mov [EXEC_PARAM_REC+2], dx`
71	`mov [EXEC_PARAM_REC+4], es`	71	`mov [EXEC_PARAM_REC+4], es`
72		72
73	`; execute command.com`	73	`; execute command.com`
74	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`	74	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`
75	`push es ;`	75	`push es ;`
76	`pop ds ;`	76	`pop ds ;`
77	`;mov dx, COMSPEC ; DS:DX - ASCIZ program name (preset already)`	77	`;mov dx, COMSPEC ; DS:DX - ASCIZ program name (preset already)`
78	`push cs`	78	`push cs`
79	`pop es`	79	`pop es`
80	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`	80	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`
81	`int 0x21`	81	`int 0x21`
82		82
83	`; if all went well, jump back to start`	83	`; if all went well, jump back to start`
84	`jnc skipsig`	84	`jnc skipsig`
85		85
86	`; restore DS=CS`	86	`; restore DS=CS`
87	`mov bx, cs`	87	`mov bx, cs`
88	`mov ds, bx`	88	`mov ds, bx`
89		89
90	`; update error string so it contains the error number`	90	`; update error string so it contains the error number`
91	`add al, '0'`	91	`add al, '0'`
92	`mov [ERRLOAD + 4], al`	92	`mov [ERRLOAD + 4], al`
93		93
94	`; display error message`	94	`; display error message`
95	`mov ah, 0x09`	95	`mov ah, 0x09`
96	`mov dx, ERRLOAD`	96	`mov dx, ERRLOAD`
97	`int 0x21`	97	`int 0x21`
98		98
99	`; wait for keypress`	99	`; wait for keypress`
100	`mov ah, 0x08`	100	`mov ah, 0x08`
101	`int 0x21`	101	`int 0x21`
102		102
103	`; back to program start`	103	`; back to program start`
104	`jmp skipsig`	104	`jmp skipsig`
105		105
106	`; ExecParamRec used by INT 21h, AX=4b00 (load and execute program), 14 bytes:`	106	`; ExecParamRec used by INT 21h, AX=4b00 (load and execute program), 14 bytes:`
107	`; offset size content`	107	`; offset size content`
108	`; +0 2 segment of environment for child (0 = current)`	108	`; +0 2 segment of environment for child (0 = current)`
109	`; +2 4 address of command line to place at PSP:0080`	109	`; +2 4 address of command line to place at PSP:0080`
110	`; +6 4 address of an FCB to be placed at PSP:005c`	110	`; +6 4 address of an FCB to be placed at PSP:005c`
111	`; +0Ah 4 address of an FCB to be placed at PSP:006c`	111	`; +0Ah 4 address of an FCB to be placed at PSP:006c`
112	`EXEC_PARAM_REC db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0`	112	`EXEC_PARAM_REC db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0`
113		113
114	`ERRLOAD db "ERR x, FAILED TO LOAD COMMAND.COM", 13, 10, '$'`	114	`ERRLOAD db "ERR x, FAILED TO LOAD COMMAND.COM", 13, 10, '$'`
115		115
116	`; DOS int 21h functions that I use require at least 32 bytes of stack, here I`	116	`; DOS int 21h functions that I use require at least 32 bytes of stack, here I`
117	`; allocate 64 bytes to be sure`	117	`; allocate 64 bytes to be sure`
118	`STACKBUF db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"`	118	`STACKBUF db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"`
119	`STACKPTR db "xx"`	119	`STACKPTR db "xx"`
120		120

Subversion Repositories SvarDOS

(root)/svarcom/trunk/rmod.asm @ 1141 – Rev 366 → 398