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
 
 
 
 
 
 
; 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  ; +0Ch
 
; 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 ; +0Eh
 
 
 
 
 
 
 
 
 
 
 
skipsig:         ; +1Dh
 
; 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 ax, CMDTAIL
mov [EXEC_PARAM_REC+2], ax
mov [EXEC_PARAM_REC+4], cs
 
; 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
 
; command.com tail arguments, in PSP format (length byte followed by arg)
CMDTAIL db 0
 
; 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 448	Rev 450
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`	-
29	`BUF000 db 128, 0 ; +0Ch`	-
30	`BUF064 db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"`	-
31	`BUF128 db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"`	-
32		-
33	`; offset of the COMSPEC variable in the environment block, 0 means "use`	28	`; 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`	29	`; boot drive". this value is patched by the transient part of COMMAND.COM`
35	`COMSPECPTR dw 0 ; +8Eh`	30	`COMSPECPTR dw 0 ; +0Ch`
36		31
37	`; fallback COMSPEC string used if no COMPSEC is present in the environment`	32	`; fallback COMSPEC string used if no COMPSEC is present in the environment`
38	`; drive. drive is patched by the transient part of COMMAND.COM`	33	`; drive. drive is patched by the transient part of COMMAND.COM`
39	`COMSPECBOOT db "@:\COMMAND.COM", 0 ; +90h`	34	`COMSPECBOOT db "@:\COMMAND.COM", 0 ; +0Eh`
40		-
41	`; ECHO status used by COMMAND.COM. 0 = ECHO OFF, 1 = ECHO ON`	-
42	`CMDECHO db 1 ; +9Fh`	-
43		-
44	`; segment of the first batch in batch chain. this is used by transient`	-
45	`; COMMAND.COM to chain multiple batch files (through CALL). 0 means "none".`	-
46	`BATCHCHAIN dw 0 ; +A0h`	-
47		-
48	`; original parent (segment of)`	-
49	`ORIGPARENT dd 0 ; +A2h`	-
50		35
51	`skipsig: ; +A6h`	36	`skipsig: ; +1Dh`
52		37
53	`; set up CS=DS=SS and point SP to my private stack buffer`	38	`; set up CS=DS=SS and point SP to my private stack buffer`
54	`mov ax, cs`	39	`mov ax, cs`
55	`mov ds, ax`	40	`mov ds, ax`
56	`mov es, ax`	41	`mov es, ax`
57	`mov ss, ax`	42	`mov ss, ax`
58	`mov sp, STACKPTR`	43	`mov sp, STACKPTR`
59		44
60	`; collect the exit code of previous application`	45	`; collect the exit code of previous application`
61	`mov ah, 0x4D`	46	`mov ah, 0x4D`
62	`int 0x21`	47	`int 0x21`
63	`xor ah, ah ; clear out termination status, I only want the exit code`	48	`xor ah, ah ; clear out termination status, I only want the exit code`
64	`mov [LEXCODE], ax`	49	`mov [LEXCODE], ax`
65		50
66	`; preset the default COMSPEC pointer to ES:DX (ES is already set to DS)`	51	`; preset the default COMSPEC pointer to ES:DX (ES is already set to DS)`
67	`mov dx, COMSPECBOOT`	52	`mov dx, COMSPECBOOT`
68		53
69	`; do I have a valid COMSPEC?`	54	`; do I have a valid COMSPEC?`
70	`or [COMSPECPTR], word 0`	55	`or [COMSPECPTR], word 0`
71	`jz USEDEFAULTCOMSPEC`	56	`jz USEDEFAULTCOMSPEC`
72	`; set ES:DX to actual COMSPEC`	57	`; set ES:DX to actual COMSPEC`
73	`mov es, [ENVSEG]`	58	`mov es, [ENVSEG]`
74	`mov dx, [COMSPECPTR]`	59	`mov dx, [COMSPECPTR]`
75	`USEDEFAULTCOMSPEC:`	60	`USEDEFAULTCOMSPEC:`
76		61
77	`; prepare the exec param block`	62	`; prepare the exec param block`
78	`mov ax, [ENVSEG]`	63	`mov ax, [ENVSEG]`
79	`mov [EXEC_PARAM_REC], ax`	64	`mov [EXEC_PARAM_REC], ax`
80	`mov ax, CMDTAIL`	65	`mov ax, CMDTAIL`
81	`mov [EXEC_PARAM_REC+2], ax`	66	`mov [EXEC_PARAM_REC+2], ax`
82	`mov [EXEC_PARAM_REC+4], cs`	67	`mov [EXEC_PARAM_REC+4], cs`
83		68
84	`; execute command.com`	69	`; execute command.com`
85	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`	70	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`
86	`push es ;`	71	`push es ;`
87	`pop ds ;`	72	`pop ds ;`
88	`;mov dx, COMSPEC ; DS:DX - ASCIZ program name (preset already)`	73	`;mov dx, COMSPEC ; DS:DX - ASCIZ program name (preset already)`
89	`push cs`	74	`push cs`
90	`pop es`	75	`pop es`
91	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`	76	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`
92	`int 0x21`	77	`int 0x21`
93		78
94	`; if all went well, jump back to start`	79	`; if all went well, jump back to start`
95	`jnc skipsig`	80	`jnc skipsig`
96		81
97	`; restore DS=CS`	82	`; restore DS=CS`
98	`mov bx, cs`	83	`mov bx, cs`
99	`mov ds, bx`	84	`mov ds, bx`
100		85
101	`; update error string so it contains the error number`	86	`; update error string so it contains the error number`
102	`add al, '0'`	87	`add al, '0'`
103	`mov [ERRLOAD + 4], al`	88	`mov [ERRLOAD + 4], al`
104		89
105	`; display error message`	90	`; display error message`
106	`mov ah, 0x09`	91	`mov ah, 0x09`
107	`mov dx, ERRLOAD`	92	`mov dx, ERRLOAD`
108	`int 0x21`	93	`int 0x21`
109		94
110	`; wait for keypress`	95	`; wait for keypress`
111	`mov ah, 0x08`	96	`mov ah, 0x08`
112	`int 0x21`	97	`int 0x21`
113		98
114	`; back to program start`	99	`; back to program start`
115	`jmp skipsig`	100	`jmp skipsig`
116		101
117	`; command.com tail arguments, in PSP format (length byte followed by arg)`	102	`; command.com tail arguments, in PSP format (length byte followed by arg)`
118	`CMDTAIL db 0`	103	`CMDTAIL db 0`
119		104
120	`; ExecParamRec used by INT 21h, AX=4b00 (load and execute program), 14 bytes:`	105	`; ExecParamRec used by INT 21h, AX=4b00 (load and execute program), 14 bytes:`
121	`; offset size content`	106	`; offset size content`
122	`; +0 2 segment of environment for child (0 = current)`	107	`; +0 2 segment of environment for child (0 = current)`
123	`; +2 4 address of command line to place at PSP:0080`	108	`; +2 4 address of command line to place at PSP:0080`
124	`; +6 4 address of an FCB to be placed at PSP:005c`	109	`; +6 4 address of an FCB to be placed at PSP:005c`
125	`; +0Ah 4 address of an FCB to be placed at PSP:006c`	110	`; +0Ah 4 address of an FCB to be placed at PSP:006c`
126	`EXEC_PARAM_REC db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0`	111	`EXEC_PARAM_REC db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0`
127		112
128	`ERRLOAD db "ERR x, FAILED TO LOAD COMMAND.COM", 13, 10, '$'`	113	`ERRLOAD db "ERR x, FAILED TO LOAD COMMAND.COM", 13, 10, '$'`
129		114
130	`; DOS int 21h functions that I use require at least 32 bytes of stack, here I`	115	`; DOS int 21h functions that I use require at least 32 bytes of stack, here I`
131	`; allocate 64 bytes to be sure`	116	`; allocate 64 bytes to be sure`
132	`STACKBUF db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"`	117	`STACKBUF db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"`
133	`STACKPTR db "xx"`	118	`STACKPTR db "xx"`
134		119

Subversion Repositories SvarDOS

(root)/svarcom/trunk/rmod.asm @ 1096 – Rev 448 → 450