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
 
FFU_UNUSED 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
 
; 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   ; +1Dh
 
; Program to execute, preset by SvarCOM (128 bytes, ASCIIZ)  ; +2Bh
EXECPROG dd 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
 
skipsig:         ; +ABh
 
; 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
 
; should I executed command.com or a pre-set application?
or [EXECPROG], byte 0
jz EXEC_COMMAND_COM
 
; TODO: perhaps I should call the DOS SetPSP function here? But if I do, the
;       int 21h, ah=50h call freezes...
;mov ah, 0x50           ; DOS 2+ -- Set PSP
;mov bx, cs
;int 0x21
 
; exec an application preset (by SvarCOM) in the ExecParamRec
mov ax, 0x4B00         ; DOS 2+ - load & execute program
mov dx, EXECPROG       ; DS:DX  - ASCIZ program name (preset at PSP[already)
mov bx, EXEC_PARAM_REC ; ES:BX  - parameter block pointer
int 0x21
mov [cs:EXECPROG], byte 0 ; do not run app again (+DS might have been changed)
 
jmp short skipsig      ; enforce valid ds/ss/etc (can be lost after int 21,4b)
 
EXEC_COMMAND_COM:
 
; 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
 
; zero out the exec param block (14 bytes)
mov al, 0              ; byte to write
mov cx, 14             ; how many times
mov di, EXEC_PARAM_REC ; ES:DI = destination
cld                    ; stosb must move forward
rep stosb              ; repeat cx times
 
; 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 [EXEC_PARAM_REC+2], word CMDTAIL
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 args and
; terminated with \r) - a single 0x0A byte is passed so SvarCOM knows it is
; called as respawn (as opposed to being invoked as a normal application)
; this allows multiple copies of SvarCOM to stack upon each other.
CMDTAIL db 0x01, 0x0A, 0x0D
 
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 463	Rev 465
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`	12	`org 0x100`
13		13
14	`PSP_ENVSEG equ 0x2C`	14	`PSP_ENVSEG equ 0x2C`
15		15
16	`section .text ; all goes into code segment`	16	`section .text ; all goes into code segment`
17		17
18	`; offset`	18	`; offset`
19	`SIG1 dw 0x1983 ; +0`	19	`SIG1 dw 0x1983 ; +0`
20	`SIG2 dw 0x1985 ; +2`	20	`SIG2 dw 0x1985 ; +2`
21	`SIG3 dw 0x2017 ; +4`	21	`SIG3 dw 0x2017 ; +4`
22	`SIG4 dw 0x2019 ; +6`	22	`SIG4 dw 0x2019 ; +6`
23		23
24	`FFU_UNUSED dw 0 ; +8`	24	`FFU_UNUSED dw 0 ; +8`
25		25
26	`; exit code of last application`	26	`; exit code of last application`
27	`LEXCODE dw 0 ; +0Ah`	27	`LEXCODE dw 0 ; +0Ah`
28		28
29	`; offset of the COMSPEC variable in the environment block, 0 means "use`	29	`; offset of the COMSPEC variable in the environment block, 0 means "use`
30	`; boot drive". this value is patched by the transient part of COMMAND.COM`	30	`; boot drive". this value is patched by the transient part of COMMAND.COM`
31	`COMSPECPTR dw 0 ; +0Ch`	31	`COMSPECPTR dw 0 ; +0Ch`
32		32
33	`; fallback COMSPEC string used if no COMPSEC is present in the environment`	33	`; fallback COMSPEC string used if no COMPSEC is present in the environment`
34	`; drive. drive is patched by the transient part of COMMAND.COM`	34	`; drive. drive is patched by the transient part of COMMAND.COM`
35	`COMSPECBOOT db "@:\COMMAND.COM", 0 ; +0Eh`	35	`COMSPECBOOT db "@:\COMMAND.COM", 0 ; +0Eh`
36		36
37	`; ExecParamRec used by INT 21h, AX=4b00 (load and execute program), 14 bytes:`	37	`; ExecParamRec used by INT 21h, AX=4b00 (load and execute program), 14 bytes:`
38	`; offset size content`	38	`; offset size content`
39	`; +0 2 segment of environment for child (0 = current)`	39	`; +0 2 segment of environment for child (0 = current)`
40	`; +2 4 address of command line to place at PSP:0080`	40	`; +2 4 address of command line to place at PSP:0080`
41	`; +6 4 address of an FCB to be placed at PSP:005c`	41	`; +6 4 address of an FCB to be placed at PSP:005c`
42	`; +0Ah 4 address of an FCB to be placed at PSP:006c`	42	`; +0Ah 4 address of an FCB to be placed at PSP:006c`
43	`EXEC_PARAM_REC db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ; +1Dh`	43	`EXEC_PARAM_REC db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ; +1Dh`
44		44
45	`; Program to execute, preset by SvarCOM (128 bytes, ASCIIZ) ; +2Bh`	45	`; Program to execute, preset by SvarCOM (128 bytes, ASCIIZ) ; +2Bh`
46	`EXECPROG dd 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0`	46	`EXECPROG dd 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0`
47		47
48	`skipsig: ; +ABh`	48	`skipsig: ; +ABh`
49		49
50	`; set up CS=DS=SS and point SP to my private stack buffer`	50	`; set up CS=DS=SS and point SP to my private stack buffer`
51	`mov ax, cs`	51	`mov ax, cs`
52	`mov ds, ax`	52	`mov ds, ax`
53	`mov es, ax`	53	`mov es, ax`
54	`mov ss, ax`	54	`mov ss, ax`
55	`mov sp, STACKPTR`	55	`mov sp, STACKPTR`
56		56
57	`; should I executed command.com or a pre-set application?`	57	`; should I executed command.com or a pre-set application?`
58	`or [EXECPROG], byte 0`	58	`or [EXECPROG], byte 0`
59	`jz EXEC_COMMAND_COM`	59	`jz EXEC_COMMAND_COM`
60		60
61	`; TODO: perhaps I should call the DOS SetPSP function here? But if I do, the`	61	`; TODO: perhaps I should call the DOS SetPSP function here? But if I do, the`
62	`; int 21h, ah=50h call freezes...`	62	`; int 21h, ah=50h call freezes...`
63	`;mov ah, 0x50 ; DOS 2+ -- Set PSP`	63	`;mov ah, 0x50 ; DOS 2+ -- Set PSP`
64	`;mov bx, cs`	64	`;mov bx, cs`
65	`;int 0x21`	65	`;int 0x21`
66		66
67	`; exec an application preset (by SvarCOM) in the ExecParamRec`	67	`; exec an application preset (by SvarCOM) in the ExecParamRec`
68	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`	68	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`
69	`mov dx, EXECPROG ; DS:DX - ASCIZ program name (preset at PSP[already)`	69	`mov dx, EXECPROG ; DS:DX - ASCIZ program name (preset at PSP[already)`
70	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`	70	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`
71	`int 0x21`	71	`int 0x21`
72	`mov [EXECPROG], byte 0 ; make sure to spawn command.com after app exits`	72	`mov [cs:EXECPROG], byte 0 ; do not run app again (+DS might have been changed)`
73		73
74	`jmp short skipsig ; enforce valid ds/ss/etc (can be lost after int 21,4b)`	74	`jmp short skipsig ; enforce valid ds/ss/etc (can be lost after int 21,4b)`
75		75
76	`EXEC_COMMAND_COM:`	76	`EXEC_COMMAND_COM:`
77		77
78	`; collect the exit code of previous application`	78	`; collect the exit code of previous application`
79	`mov ah, 0x4D`	79	`mov ah, 0x4D`
80	`int 0x21`	80	`int 0x21`
81	`xor ah, ah ; clear out termination status, I only want the exit code`	81	`xor ah, ah ; clear out termination status, I only want the exit code`
82	`mov [LEXCODE], ax`	82	`mov [LEXCODE], ax`
83		83
84	`; zero out the exec param block (14 bytes)`	84	`; zero out the exec param block (14 bytes)`
85	`mov al, 0 ; byte to write`	85	`mov al, 0 ; byte to write`
86	`mov cx, 14 ; how many times`	86	`mov cx, 14 ; how many times`
87	`mov di, EXEC_PARAM_REC ; ES:DI = destination`	87	`mov di, EXEC_PARAM_REC ; ES:DI = destination`
88	`cld ; stosb must move forward`	88	`cld ; stosb must move forward`
89	`rep stosb ; repeat cx times`	89	`rep stosb ; repeat cx times`
90		90
91	`; preset the default COMSPEC pointer to ES:DX (ES is already set to DS)`	91	`; preset the default COMSPEC pointer to ES:DX (ES is already set to DS)`
92	`mov dx, COMSPECBOOT`	92	`mov dx, COMSPECBOOT`
93		93
94	`; do I have a valid COMSPEC?`	94	`; do I have a valid COMSPEC?`
95	`or [COMSPECPTR], word 0`	95	`or [COMSPECPTR], word 0`
96	`jz USEDEFAULTCOMSPEC`	96	`jz USEDEFAULTCOMSPEC`
97	`; set ES:DX to actual COMSPEC (in env segment)`	97	`; set ES:DX to actual COMSPEC (in env segment)`
98	`mov es, [PSP_ENVSEG]`	98	`mov es, [PSP_ENVSEG]`
99	`mov dx, [COMSPECPTR]`	99	`mov dx, [COMSPECPTR]`
100	`USEDEFAULTCOMSPEC:`	100	`USEDEFAULTCOMSPEC:`
101		101
102	`; prepare the exec param block`	102	`; prepare the exec param block`
103	`mov ax, [PSP_ENVSEG]`	103	`mov ax, [PSP_ENVSEG]`
104	`mov [EXEC_PARAM_REC], ax`	104	`mov [EXEC_PARAM_REC], ax`
105	`mov ax, CMDTAIL`	-
106	`mov [EXEC_PARAM_REC+2], ax`	105	`mov [EXEC_PARAM_REC+2], word CMDTAIL`
107	`mov [EXEC_PARAM_REC+4], cs`	106	`mov [EXEC_PARAM_REC+4], cs`
108		107
109	`; execute command.com`	108	`; execute command.com`
110	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`	109	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`
111	`push es ;`	110	`push es ;`
112	`pop ds ;`	111	`pop ds ;`
113	`;mov dx, COMSPEC ; DS:DX - ASCIZ program name (preset already)`	112	`;mov dx, COMSPEC ; DS:DX - ASCIZ program name (preset already)`
114	`push cs`	113	`push cs`
115	`pop es`	114	`pop es`
116	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`	115	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`
117	`int 0x21`	116	`int 0x21`
118		117
119	`; if all went well, jump back to start`	118	`; if all went well, jump back to start`
120	`jnc skipsig`	119	`jnc skipsig`
121		120
122	`; restore DS=CS`	121	`; restore DS=CS`
123	`mov bx, cs`	122	`mov bx, cs`
124	`mov ds, bx`	123	`mov ds, bx`
125		124
126	`; update error string so it contains the error number`	125	`; update error string so it contains the error number`
127	`add al, '0'`	126	`add al, '0'`
128	`mov [ERRLOAD + 4], al`	127	`mov [ERRLOAD + 4], al`
129		128
130	`; display error message`	129	`; display error message`
131	`mov ah, 0x09`	130	`mov ah, 0x09`
132	`mov dx, ERRLOAD`	131	`mov dx, ERRLOAD`
133	`int 0x21`	132	`int 0x21`
134		133
135	`; wait for keypress`	134	`; wait for keypress`
136	`mov ah, 0x08`	135	`mov ah, 0x08`
137	`int 0x21`	136	`int 0x21`
138		137
139	`; back to program start`	138	`; back to program start`
140	`jmp skipsig`	139	`jmp skipsig`
141		140
142	`; command.com tail arguments, in PSP format: length byte followed by args and`	141	`; command.com tail arguments, in PSP format: length byte followed by args and`
143	`; terminated with \r)`	142	`; terminated with \r) - a single 0x0A byte is passed so SvarCOM knows it is`
-		143	`; called as respawn (as opposed to being invoked as a normal application)`
-		144	`; this allows multiple copies of SvarCOM to stack upon each other.`
144	`CMDTAIL db 0x00, 0x0D`	145	`CMDTAIL db 0x01, 0x0A, 0x0D`
145		146
146	`ERRLOAD db "ERR x, FAILED TO LOAD COMMAND.COM", 13, 10, '$'`	147	`ERRLOAD db "ERR x, FAILED TO LOAD COMMAND.COM", 13, 10, '$'`
147		148
148	`; DOS int 21h functions that I use require at least 32 bytes of stack, here I`	149	`; DOS int 21h functions that I use require at least 32 bytes of stack, here I`
149	`; allocate 64 bytes to be sure`	150	`; allocate 64 bytes to be sure`
150	`STACKBUF db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"`	151	`STACKBUF db "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF"`
151	`STACKPTR db "xx"`	152	`STACKPTR db "xx"`
152		153

Subversion Repositories SvarDOS

(root)/svarcom/trunk/rmod.asm @ 1037 – Rev 463 → 465