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 0x100
 
PSP_ENVSEG equ 0x2C
 
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 (in env segment)
mov es, [PSP_ENVSEG]
mov dx, [COMSPECPTR]
USEDEFAULTCOMSPEC:
 
; prepare the exec param block
mov ax, [PSP_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 450	Rev 459
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 0x100`
-		13
12	`org 0h ; this is meant to be executed without a PSP`	14	`PSP_ENVSEG equ 0x2C`
13		15
14	`section .text ; all goes into code segment`	16	`section .text ; all goes into code segment`
15		17
16	`; offset`	18	`; offset`
17	`SIG1 dw 0x1983 ; +0`	19	`SIG1 dw 0x1983 ; +0`
18	`SIG2 dw 0x1985 ; +2`	20	`SIG2 dw 0x1985 ; +2`
19	`SIG3 dw 0x2017 ; +4`	21	`SIG3 dw 0x2017 ; +4`
20	`SIG4 dw 0x2019 ; +6`	22	`SIG4 dw 0x2019 ; +6`
21		23
22	`; environment segment - this is updated by SvarCOM at init time`	24	`; environment segment - this is updated by SvarCOM at init time`
23	`ENVSEG dw 0 ; +8`	25	`ENVSEG dw 0 ; +8`
24		26
25	`; exit code of last application`	27	`; exit code of last application`
26	`LEXCODE dw 0 ; +0Ah`	28	`LEXCODE dw 0 ; +0Ah`
27		29
28	`; offset of the COMSPEC variable in the environment block, 0 means "use`	30	`; offset of the COMSPEC variable in the environment block, 0 means "use`
29	`; boot drive". this value is patched by the transient part of COMMAND.COM`	31	`; boot drive". this value is patched by the transient part of COMMAND.COM`
30	`COMSPECPTR dw 0 ; +0Ch`	32	`COMSPECPTR dw 0 ; +0Ch`
31		33
32	`; fallback COMSPEC string used if no COMPSEC is present in the environment`	34	`; fallback COMSPEC string used if no COMPSEC is present in the environment`
33	`; drive. drive is patched by the transient part of COMMAND.COM`	35	`; drive. drive is patched by the transient part of COMMAND.COM`
34	`COMSPECBOOT db "@:\COMMAND.COM", 0 ; +0Eh`	36	`COMSPECBOOT db "@:\COMMAND.COM", 0 ; +0Eh`
35		37
36	`skipsig: ; +1Dh`	38	`skipsig: ; +1Dh`
37		39
38	`; set up CS=DS=SS and point SP to my private stack buffer`	40	`; set up CS=DS=SS and point SP to my private stack buffer`
39	`mov ax, cs`	41	`mov ax, cs`
40	`mov ds, ax`	42	`mov ds, ax`
41	`mov es, ax`	43	`mov es, ax`
42	`mov ss, ax`	44	`mov ss, ax`
43	`mov sp, STACKPTR`	45	`mov sp, STACKPTR`
44		46
45	`; collect the exit code of previous application`	47	`; collect the exit code of previous application`
46	`mov ah, 0x4D`	48	`mov ah, 0x4D`
47	`int 0x21`	49	`int 0x21`
48	`xor ah, ah ; clear out termination status, I only want the exit code`	50	`xor ah, ah ; clear out termination status, I only want the exit code`
49	`mov [LEXCODE], ax`	51	`mov [LEXCODE], ax`
50		52
51	`; preset the default COMSPEC pointer to ES:DX (ES is already set to DS)`	53	`; preset the default COMSPEC pointer to ES:DX (ES is already set to DS)`
52	`mov dx, COMSPECBOOT`	54	`mov dx, COMSPECBOOT`
53		55
54	`; do I have a valid COMSPEC?`	56	`; do I have a valid COMSPEC?`
55	`or [COMSPECPTR], word 0`	57	`or [COMSPECPTR], word 0`
56	`jz USEDEFAULTCOMSPEC`	58	`jz USEDEFAULTCOMSPEC`
57	`; set ES:DX to actual COMSPEC`	59	`; set ES:DX to actual COMSPEC (in env segment)`
58	`mov es, [ENVSEG]`	60	`mov es, [PSP_ENVSEG]`
59	`mov dx, [COMSPECPTR]`	61	`mov dx, [COMSPECPTR]`
60	`USEDEFAULTCOMSPEC:`	62	`USEDEFAULTCOMSPEC:`
61		63
62	`; prepare the exec param block`	64	`; prepare the exec param block`
63	`mov ax, [ENVSEG]`	65	`mov ax, [PSP_ENVSEG]`
64	`mov [EXEC_PARAM_REC], ax`	66	`mov [EXEC_PARAM_REC], ax`
65	`mov ax, CMDTAIL`	67	`mov ax, CMDTAIL`
66	`mov [EXEC_PARAM_REC+2], ax`	68	`mov [EXEC_PARAM_REC+2], ax`
67	`mov [EXEC_PARAM_REC+4], cs`	69	`mov [EXEC_PARAM_REC+4], cs`
68		70
69	`; execute command.com`	71	`; execute command.com`
70	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`	72	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`
71	`push es ;`	73	`push es ;`
72	`pop ds ;`	74	`pop ds ;`
73	`;mov dx, COMSPEC ; DS:DX - ASCIZ program name (preset already)`	75	`;mov dx, COMSPEC ; DS:DX - ASCIZ program name (preset already)`
74	`push cs`	76	`push cs`
75	`pop es`	77	`pop es`
76	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`	78	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`
77	`int 0x21`	79	`int 0x21`
78		80
79	`; if all went well, jump back to start`	81	`; if all went well, jump back to start`
80	`jnc skipsig`	82	`jnc skipsig`
81		83
82	`; restore DS=CS`	84	`; restore DS=CS`
83	`mov bx, cs`	85	`mov bx, cs`
84	`mov ds, bx`	86	`mov ds, bx`
85		87
86	`; update error string so it contains the error number`	88	`; update error string so it contains the error number`
87	`add al, '0'`	89	`add al, '0'`
88	`mov [ERRLOAD + 4], al`	90	`mov [ERRLOAD + 4], al`
89		91
90	`; display error message`	92	`; display error message`
91	`mov ah, 0x09`	93	`mov ah, 0x09`
92	`mov dx, ERRLOAD`	94	`mov dx, ERRLOAD`
93	`int 0x21`	95	`int 0x21`
94		96
95	`; wait for keypress`	97	`; wait for keypress`
96	`mov ah, 0x08`	98	`mov ah, 0x08`
97	`int 0x21`	99	`int 0x21`
98		100
99	`; back to program start`	101	`; back to program start`
100	`jmp skipsig`	102	`jmp skipsig`
101		103
102	`; command.com tail arguments, in PSP format (length byte followed by arg)`	104	`; command.com tail arguments, in PSP format (length byte followed by arg)`
103	`CMDTAIL db 0`	105	`CMDTAIL db 0`
104		106
105	`; ExecParamRec used by INT 21h, AX=4b00 (load and execute program), 14 bytes:`	107	`; ExecParamRec used by INT 21h, AX=4b00 (load and execute program), 14 bytes:`
106	`; offset size content`	108	`; offset size content`
107	`; +0 2 segment of environment for child (0 = current)`	109	`; +0 2 segment of environment for child (0 = current)`
108	`; +2 4 address of command line to place at PSP:0080`	110	`; +2 4 address of command line to place at PSP:0080`
109	`; +6 4 address of an FCB to be placed at PSP:005c`	111	`; +6 4 address of an FCB to be placed at PSP:005c`
110	`; +0Ah 4 address of an FCB to be placed at PSP:006c`	112	`; +0Ah 4 address of an FCB to be placed at PSP:006c`
111	`EXEC_PARAM_REC db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0`	113	`EXEC_PARAM_REC db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0`
112		114
113	`ERRLOAD db "ERR x, FAILED TO LOAD COMMAND.COM", 13, 10, '$'`	115	`ERRLOAD db "ERR x, FAILED TO LOAD COMMAND.COM", 13, 10, '$'`
114		116
115	`; DOS int 21h functions that I use require at least 32 bytes of stack, here I`	117	`; DOS int 21h functions that I use require at least 32 bytes of stack, here I`
116	`; allocate 64 bytes to be sure`	118	`; allocate 64 bytes to be sure`
117	`STACKBUF db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"`	119	`STACKBUF db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"`
118	`STACKPTR db "xx"`	120	`STACKPTR db "xx"`
119		121

Subversion Repositories SvarDOS

(root)/svarcom/trunk/rmod.asm @ 1084 – Rev 450 → 459