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


;
; rmod - resident module of the SvarCOM command interpreter (NASM code)
;
; 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  this acts also as a guardval to detect stack overflows
 
; DOS int 21h functions that I use require at least 40 bytes of stack under
; DOS-C (FreeDOS) kernel, so here I reserve 64 bytes juste to be sure
STACKBUF db "XXX  SVARCOM RMOD BY MATEUSZ VISTE  XXXXXXXXXXXXXXXXXXXXXXXXXXXX"
STACKPTR dw 0
 
; 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  ; +4Ah
 
; 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 ; +4Ch
 
; exit code of last application
LEXCODE  db 0    ; +5Bh
 
; 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   ; +5Ch
 
; Program to execute, preset by SvarCOM (128 bytes, ASCIIZ)  ; +6Ah
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
 
; offset within EXECPROG for out and in filenames in case stdin or stdout
; needs to be redirected (0xffff=no redirection)
REDIR_OUTFIL dw 0xffff    ; +EAh
REDIR_INFIL dw 0xffff     ; +ECh
REDIR_OUTAPPEND dw 0      ; +EEh
 
; CTRL+BREAK (int 23h) handler
; According to the TechHelp! Manual: "If you want to abort (exit to the parent
; process), then set the carry flag and return via a FAR RET. This causes DOS
; to perform normal cleanup and exit to the parent." (otherwise use iret)
BREAK_HANDLER:            ; +F0h
stc
retf
 
 
skipsig:                  ; +F2h
 
; 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
 
; set up myself as break handler
mov ax, 0x2523  ; set int vector 23h
mov dx, BREAK_HANDLER
int 0x21
 
; revert stdin/stdout redirections (if any) to their initial state
call REVERT_REDIR_IF_ANY
 
; redirect stdout if required
call REDIR_INOUTFILE_IF_REQUIRED
 
; 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
mov [LEXCODE], al
 
; 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, '$'
 
; variables used to revert stdin/stdout to their initial state
OLD_STDOUT dw 0xffff
OLD_STDIN  dw 0xffff
 
 
; ****************************************************************************
; *** ROUTINES ***************************************************************
; ****************************************************************************
 
; ----------------------------------------------------------------------------
; revert stdin/stdout redirections (if any) to their initial state
; all memory accesses are CS-prefixes because this code may be called at
; times when DS is out of whack.
REVERT_REDIR_IF_ANY:
; is stdout redirected?
mov bx, [OLD_STDOUT]
cmp bx, 0xffff
je STDOUT_DONE
; revert the stdout handle (dst in BX already)
mov cx, 1        ; src handle (1=stdout)
mov ah, 0x46     ; redirect a handle
int 0x21
; close the old handle (still in bx)
mov ah, 0x3e
int 0x21
mov [OLD_STDOUT], word 0xffff ; mark stdout as "not redirected"
STDOUT_DONE:
 
; is stdin redirected?
mov bx, [OLD_STDIN]
cmp bx, 0xffff
je STDIN_DONE
; revert the stdout handle (dst in BX already)
xor cx, cx       ; src handle (0=stdin)
mov ah, 0x46     ; redirect a handle
int 0x21
; close the old handle (still in bx)
mov ah, 0x3e
int 0x21
mov [OLD_STDIN], word 0xffff ; mark stdin as "not redirected"
STDIN_DONE:
 
ret
; ----------------------------------------------------------------------------
 
 
; ----------------------------------------------------------------------------
; redirect stdout if REDIR_OUTFIL points to something
REDIR_INOUTFILE_IF_REQUIRED:
mov si, [REDIR_OUTFIL]
cmp si, 0xffff
je NO_STDOUT_REDIR
add si, EXECPROG       ; si=output file
mov ax, 0x6c00         ; Extended Open/Create
mov bx, 1              ; access mode (0=read, 1=write, 2=r+w)
xor cx, cx             ; file attribs when(if) file is created (0=normal)
mov dx, [REDIR_OUTAPPEND] ; action if file exist (0x11=open, 0x12=truncate)
int 0x21               ; ax=handle on success (CF clear)
mov [REDIR_OUTFIL], word 0xffff
jc NO_STDOUT_REDIR     ; TODO: abort with an error message instead
 
; jump to end of file if flag was 0x11 (required for >> redirections)
cmp [REDIR_OUTAPPEND], word 0x11
jne SKIP_JMPEOF
mov bx, ax
mov ax, 0x4202         ; jump to position EOF - CX:DX in handle BX
xor cx, cx
xor dx, dx
int 0x21
mov ax, bx             ; put my handle back in ax, as expected by later code
SKIP_JMPEOF:
 
; duplicate current stdout so I can revert it later
push ax                ; save my file handle in stack
mov ah, 0x45           ; duplicate file handle BX
mov bx, 1              ; 1=stdout
int 0x21               ; ax=new (duplicated) file handle
mov [OLD_STDOUT], ax   ; save the old handle in memory
 
; redirect stdout to my file
pop bx                 ; dst handle
mov cx, 1              ; src handle (1=stdout)
mov ah, 0x46           ; "redirect a handle"
int 0x21
 
; close the original file handle, I no longer need it
mov ah, 0x3e           ; close a file handle (handle in BX)
int 0x21
NO_STDOUT_REDIR:
 
; *** redirect stdin if REDIR_INFIL points to something ***
mov dx, [REDIR_INFIL]
cmp dx, 0xffff
je NO_STDIN_REDIR
add dx, EXECPROG       ; ds:dx=file
mov ax, 0x3d00         ; open file for read
int 0x21               ; ax=handle on success (CF clear)
mov [REDIR_INFIL], word 0xffff
jc NO_STDIN_REDIR      ; TODO: abort with an error message instead
 
; duplicate current stdin so I can revert it later
push ax                ; save my file handle in stack
mov ah, 0x45           ; duplicate file handle BX
xor bx, bx             ; 0=stdin
int 0x21               ; ax=new (duplicated) file handle
mov [OLD_STDIN], ax    ; save the old handle in memory
 
; redirect stdout to my file
pop bx                 ; dst handle
xor cx, cx             ; src handle (0=stdin)
mov ah, 0x46           ; "redirect a handle"
int 0x21
 
; close the original file handle, I no longer need it
mov ah, 0x3e           ; close a file handle (handle in BX)
int 0x21
NO_STDIN_REDIR:
ret
; ----------------------------------------------------------------------------
 

Rev 537	Rev 543
1	`;`	1	`;`
2	`; rmod - resident module of the SvarCOM command interpreter (NASM code)`	2	`; rmod - resident module of the SvarCOM command interpreter (NASM code)`
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 this acts also as a guardval to detect stack overflows`	22	`SIG4 dw 0x2019 ; +6 this acts also as a guardval to detect stack overflows`
23		23
24	`; DOS int 21h functions that I use require at least 40 bytes of stack under`	24	`; DOS int 21h functions that I use require at least 40 bytes of stack under`
25	`; DOS-C (FreeDOS) kernel, so here I reserve 64 bytes juste to be sure`	25	`; DOS-C (FreeDOS) kernel, so here I reserve 64 bytes juste to be sure`
26	`STACKBUF db "XXX SVARCOM RMOD BY MATEUSZ VISTE XXXXXXXXXXXXXXXXXXXXXXXXXXXX"`	26	`STACKBUF db "XXX SVARCOM RMOD BY MATEUSZ VISTE XXXXXXXXXXXXXXXXXXXXXXXXXXXX"`
27	`STACKPTR dw 0`	27	`STACKPTR dw 0`
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 ; +4Ah`	31	`COMSPECPTR dw 0 ; +4Ah`
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 ; +4Ch`	35	`COMSPECBOOT db "@:\COMMAND.COM", 0 ; +4Ch`
36		36
37	`; exit code of last application`	37	`; exit code of last application`
38	`LEXCODE db 0 ; +5Bh`	38	`LEXCODE db 0 ; +5Bh`
39		39
40	`; ExecParamRec used by INT 21h, AX=4b00 (load and execute program), 14 bytes:`	40	`; ExecParamRec used by INT 21h, AX=4b00 (load and execute program), 14 bytes:`
41	`; offset size content`	41	`; offset size content`
42	`; +0 2 segment of environment for child (0 = current)`	42	`; +0 2 segment of environment for child (0 = current)`
43	`; +2 4 address of command line to place at PSP:0080`	43	`; +2 4 address of command line to place at PSP:0080`
44	`; +6 4 address of an FCB to be placed at PSP:005c`	44	`; +6 4 address of an FCB to be placed at PSP:005c`
45	`; +0Ah 4 address of an FCB to be placed at PSP:006c`	45	`; +0Ah 4 address of an FCB to be placed at PSP:006c`
46	`EXEC_PARAM_REC db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ; +5Ch`	46	`EXEC_PARAM_REC db 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ; +5Ch`
47		47
48	`; Program to execute, preset by SvarCOM (128 bytes, ASCIIZ) ; +6Ah`	48	`; Program to execute, preset by SvarCOM (128 bytes, ASCIIZ) ; +6Ah`
49	`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`	49	`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`
50		50
51	`; offset within EXECPROG for out and in filenames in case stdin or stdout`	51	`; offset within EXECPROG for out and in filenames in case stdin or stdout`
52	`; needs to be redirected (0xffff=no redirection)`	52	`; needs to be redirected (0xffff=no redirection)`
53	`REDIR_OUTFIL dw 0xffff ; +EAh`	53	`REDIR_OUTFIL dw 0xffff ; +EAh`
54	`REDIR_INFIL dw 0xffff ; +ECh`	54	`REDIR_INFIL dw 0xffff ; +ECh`
55	`REDIR_OUTAPPEND dw 0 ; +EEh`	55	`REDIR_OUTAPPEND dw 0 ; +EEh`
56		56
57	`; CTRL+BREAK (int 23h) handler`	57	`; CTRL+BREAK (int 23h) handler`
58	`; According to the TechHelp! Manual: "If you want to abort (exit to the parent`	58	`; According to the TechHelp! Manual: "If you want to abort (exit to the parent`
59	`; process), then set the carry flag and return via a FAR RET. This causes DOS`	59	`; process), then set the carry flag and return via a FAR RET. This causes DOS`
60	`; to perform normal cleanup and exit to the parent." (otherwise use iret)`	60	`; to perform normal cleanup and exit to the parent." (otherwise use iret)`
61	`BREAK_HANDLER: ; +F0h`	61	`BREAK_HANDLER: ; +F0h`
62	`stc`	62	`stc`
63	`retf`	63	`retf`
64		64
65		65
66	`skipsig: ; +F2h`	66	`skipsig: ; +F2h`
67		67
68	`; set up CS=DS=SS and point SP to my private stack buffer`	68	`; set up CS=DS=SS and point SP to my private stack buffer`
69	`mov ax, cs`	69	`mov ax, cs`
70	`mov ds, ax`	70	`mov ds, ax`
71	`mov es, ax`	71	`mov es, ax`
72	`mov ss, ax`	72	`mov ss, ax`
73	`mov sp, STACKPTR`	73	`mov sp, STACKPTR`
74		74
75	`; set up myself as break handler`	75	`; set up myself as break handler`
76	`mov ax, 0x2523 ; set int vector 23h`	76	`mov ax, 0x2523 ; set int vector 23h`
77	`mov dx, BREAK_HANDLER`	77	`mov dx, BREAK_HANDLER`
78	`int 0x21`	78	`int 0x21`
79		79
80	`; revert stdin/stdout redirections (if any) to their initial state`	80	`; revert stdin/stdout redirections (if any) to their initial state`
81	`call REVERT_REDIR_IF_ANY`	81	`call REVERT_REDIR_IF_ANY`
82		82
83	`; redirect stdout if required`	83	`; redirect stdout if required`
84	`call REDIR_OUTFILE_IF_REQUIRED`	84	`call REDIR_INOUTFILE_IF_REQUIRED`
85		85
86	`; should I executed command.com or a pre-set application?`	86	`; should I executed command.com or a pre-set application?`
87	`or [EXECPROG], byte 0`	87	`or [EXECPROG], byte 0`
88	`jz EXEC_COMMAND_COM`	88	`jz EXEC_COMMAND_COM`
89		89
90	`; TODO: perhaps I should call the DOS SetPSP function here? But if I do, the`	90	`; TODO: perhaps I should call the DOS SetPSP function here? But if I do, the`
91	`; int 21h, ah=50h call freezes...`	91	`; int 21h, ah=50h call freezes...`
92	`;mov ah, 0x50 ; DOS 2+ -- Set PSP`	92	`;mov ah, 0x50 ; DOS 2+ -- Set PSP`
93	`;mov bx, cs`	93	`;mov bx, cs`
94	`;int 0x21`	94	`;int 0x21`
95		95
96	`; exec an application preset (by SvarCOM) in the ExecParamRec`	96	`; exec an application preset (by SvarCOM) in the ExecParamRec`
97	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`	97	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`
98	`mov dx, EXECPROG ; DS:DX - ASCIZ program name (preset at PSP[already)`	98	`mov dx, EXECPROG ; DS:DX - ASCIZ program name (preset at PSP[already)`
99	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`	99	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`
100	`int 0x21`	100	`int 0x21`
101	`mov [cs:EXECPROG], byte 0 ; do not run app again (+DS might have been changed)`	101	`mov [cs:EXECPROG], byte 0 ; do not run app again (+DS might have been changed)`
102		102
103	`jmp short skipsig ; enforce valid ds/ss/etc (can be lost after int 21,4b)`	103	`jmp short skipsig ; enforce valid ds/ss/etc (can be lost after int 21,4b)`
104		104
105	`EXEC_COMMAND_COM:`	105	`EXEC_COMMAND_COM:`
106		106
107	`; collect the exit code of previous application`	107	`; collect the exit code of previous application`
108	`mov ah, 0x4D`	108	`mov ah, 0x4D`
109	`int 0x21`	109	`int 0x21`
110	`mov [LEXCODE], al`	110	`mov [LEXCODE], al`
111		111
112	`; zero out the exec param block (14 bytes)`	112	`; zero out the exec param block (14 bytes)`
113	`mov al, 0 ; byte to write`	113	`mov al, 0 ; byte to write`
114	`mov cx, 14 ; how many times`	114	`mov cx, 14 ; how many times`
115	`mov di, EXEC_PARAM_REC ; ES:DI = destination`	115	`mov di, EXEC_PARAM_REC ; ES:DI = destination`
116	`cld ; stosb must move forward`	116	`cld ; stosb must move forward`
117	`rep stosb ; repeat cx times`	117	`rep stosb ; repeat cx times`
118		118
119	`; preset the default COMSPEC pointer to ES:DX (ES is already set to DS)`	119	`; preset the default COMSPEC pointer to ES:DX (ES is already set to DS)`
120	`mov dx, COMSPECBOOT`	120	`mov dx, COMSPECBOOT`
121		121
122	`; do I have a valid COMSPEC?`	122	`; do I have a valid COMSPEC?`
123	`or [COMSPECPTR], word 0`	123	`or [COMSPECPTR], word 0`
124	`jz USEDEFAULTCOMSPEC`	124	`jz USEDEFAULTCOMSPEC`
125	`; set ES:DX to actual COMSPEC (in env segment)`	125	`; set ES:DX to actual COMSPEC (in env segment)`
126	`mov es, [PSP_ENVSEG]`	126	`mov es, [PSP_ENVSEG]`
127	`mov dx, [COMSPECPTR]`	127	`mov dx, [COMSPECPTR]`
128	`USEDEFAULTCOMSPEC:`	128	`USEDEFAULTCOMSPEC:`
129		129
130	`; prepare the exec param block`	130	`; prepare the exec param block`
131	`mov ax, [PSP_ENVSEG]`	131	`mov ax, [PSP_ENVSEG]`
132	`mov [EXEC_PARAM_REC], ax`	132	`mov [EXEC_PARAM_REC], ax`
133	`mov [EXEC_PARAM_REC+2], word CMDTAIL`	133	`mov [EXEC_PARAM_REC+2], word CMDTAIL`
134	`mov [EXEC_PARAM_REC+4], cs`	134	`mov [EXEC_PARAM_REC+4], cs`
135		135
136	`; execute command.com`	136	`; execute command.com`
137	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`	137	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`
138	`push es ;`	138	`push es ;`
139	`pop ds ;`	139	`pop ds ;`
140	`;mov dx, COMSPEC ; DS:DX - ASCIZ program name (preset already)`	140	`;mov dx, COMSPEC ; DS:DX - ASCIZ program name (preset already)`
141	`push cs`	141	`push cs`
142	`pop es`	142	`pop es`
143	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`	143	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`
144	`int 0x21`	144	`int 0x21`
145		145
146	`; if all went well, jump back to start`	146	`; if all went well, jump back to start`
147	`jnc skipsig`	147	`jnc skipsig`
148		148
149	`; restore DS=CS`	149	`; restore DS=CS`
150	`mov bx, cs`	150	`mov bx, cs`
151	`mov ds, bx`	151	`mov ds, bx`
152		152
153	`; update error string so it contains the error number`	153	`; update error string so it contains the error number`
154	`add al, '0'`	154	`add al, '0'`
155	`mov [ERRLOAD + 4], al`	155	`mov [ERRLOAD + 4], al`
156		156
157	`; display error message`	157	`; display error message`
158	`mov ah, 0x09`	158	`mov ah, 0x09`
159	`mov dx, ERRLOAD`	159	`mov dx, ERRLOAD`
160	`int 0x21`	160	`int 0x21`
161		161
162	`; wait for keypress`	162	`; wait for keypress`
163	`mov ah, 0x08`	163	`mov ah, 0x08`
164	`int 0x21`	164	`int 0x21`
165		165
166	`; back to program start`	166	`; back to program start`
167	`jmp skipsig`	167	`jmp skipsig`
168		168
169	`; command.com tail arguments, in PSP format: length byte followed by args and`	169	`; command.com tail arguments, in PSP format: length byte followed by args and`
170	`; terminated with \r) - a single 0x0A byte is passed so SvarCOM knows it is`	170	`; terminated with \r) - a single 0x0A byte is passed so SvarCOM knows it is`
171	`; called as respawn (as opposed to being invoked as a normal application)`	171	`; called as respawn (as opposed to being invoked as a normal application)`
172	`; this allows multiple copies of SvarCOM to stack upon each other.`	172	`; this allows multiple copies of SvarCOM to stack upon each other.`
173	`CMDTAIL db 0x01, 0x0A, 0x0D`	173	`CMDTAIL db 0x01, 0x0A, 0x0D`
174		174
175	`ERRLOAD db "ERR x, FAILED TO LOAD COMMAND.COM", 13, 10, '$'`	175	`ERRLOAD db "ERR x, FAILED TO LOAD COMMAND.COM", 13, 10, '$'`
176		176
177	`; variables used to revert stdin/stdout to their initial state`	177	`; variables used to revert stdin/stdout to their initial state`
178	`OLD_STDOUT dw 0xffff`	178	`OLD_STDOUT dw 0xffff`
179	`OLD_STDIN dw 0xffff`	179	`OLD_STDIN dw 0xffff`
180		180
181		181
182	`; ****************************************************************************`	182	`; ****************************************************************************`
183	`; * ROUTINES *************************************************************`	183	`; * ROUTINES *************************************************************`
184	`; ****************************************************************************`	184	`; ****************************************************************************`
185		185
186	`; ----------------------------------------------------------------------------`	186	`; ----------------------------------------------------------------------------`
187	`; revert stdin/stdout redirections (if any) to their initial state`	187	`; revert stdin/stdout redirections (if any) to their initial state`
188	`; all memory accesses are CS-prefixes because this code may be called at`	188	`; all memory accesses are CS-prefixes because this code may be called at`
189	`; times when DS is out of whack.`	189	`; times when DS is out of whack.`
190	`REVERT_REDIR_IF_ANY:`	190	`REVERT_REDIR_IF_ANY:`
191	`; is stdout redirected?`	191	`; is stdout redirected?`
192	`mov bx, [OLD_STDOUT]`	192	`mov bx, [OLD_STDOUT]`
193	`cmp bx, 0xffff`	193	`cmp bx, 0xffff`
194	`je STDOUT_DONE`	194	`je STDOUT_DONE`
195	`; revert the stdout handle (dst in BX already)`	195	`; revert the stdout handle (dst in BX already)`
196	`mov cx, 1 ; src handle (1=stdout)`	196	`mov cx, 1 ; src handle (1=stdout)`
197	`mov ah, 0x46 ; redirect a handle`	197	`mov ah, 0x46 ; redirect a handle`
198	`int 0x21`	198	`int 0x21`
199	`; close the old handle (still in bx)`	199	`; close the old handle (still in bx)`
200	`mov ah, 0x3e`	200	`mov ah, 0x3e`
201	`int 0x21`	201	`int 0x21`
202	`mov [OLD_STDOUT], word 0xffff ; mark stdout as "not redirected"`	202	`mov [OLD_STDOUT], word 0xffff ; mark stdout as "not redirected"`
203	`STDOUT_DONE:`	203	`STDOUT_DONE:`
-		204
-		205	`; is stdin redirected?`
-		206	`mov bx, [OLD_STDIN]`
-		207	`cmp bx, 0xffff`
-		208	`je STDIN_DONE`
-		209	`; revert the stdout handle (dst in BX already)`
-		210	`xor cx, cx ; src handle (0=stdin)`
-		211	`mov ah, 0x46 ; redirect a handle`
-		212	`int 0x21`
-		213	`; close the old handle (still in bx)`
-		214	`mov ah, 0x3e`
-		215	`int 0x21`
-		216	`mov [OLD_STDIN], word 0xffff ; mark stdin as "not redirected"`
-		217	`STDIN_DONE:`
-		218
204	`ret`	219	`ret`
205	`; ----------------------------------------------------------------------------`	220	`; ----------------------------------------------------------------------------`
206		221
207		222
208	`; ----------------------------------------------------------------------------`	223	`; ----------------------------------------------------------------------------`
209	`; redirect stdout if REDIR_OUTFIL points to something`	224	`; redirect stdout if REDIR_OUTFIL points to something`
210	`REDIR_OUTFILE_IF_REQUIRED:`	225	`REDIR_INOUTFILE_IF_REQUIRED:`
211	`mov si, [REDIR_OUTFIL]`	226	`mov si, [REDIR_OUTFIL]`
212	`cmp si, 0xffff`	227	`cmp si, 0xffff`
213	`je NO_STDOUT_REDIR`	228	`je NO_STDOUT_REDIR`
214	`add si, EXECPROG ; si=output file`	229	`add si, EXECPROG ; si=output file`
215	`mov ax, 0x6c00 ; Extended Open/Create`	230	`mov ax, 0x6c00 ; Extended Open/Create`
216	`mov bx, 1 ; access mode (0=read, 1=write, 2=r+w)`	231	`mov bx, 1 ; access mode (0=read, 1=write, 2=r+w)`
217	`xor cx, cx ; file attribs when(if) file is created (0=normal)`	232	`xor cx, cx ; file attribs when(if) file is created (0=normal)`
218	`mov dx, [REDIR_OUTAPPEND] ; action if file exist (0x11=open, 0x12=truncate)`	233	`mov dx, [REDIR_OUTAPPEND] ; action if file exist (0x11=open, 0x12=truncate)`
219	`int 0x21 ; ax=handle on success (CF clear)`	234	`int 0x21 ; ax=handle on success (CF clear)`
220	`mov [REDIR_OUTFIL], word 0xffff`	235	`mov [REDIR_OUTFIL], word 0xffff`
221	`jc NO_STDOUT_REDIR ; TODO: abort with an error message instead`	236	`jc NO_STDOUT_REDIR ; TODO: abort with an error message instead`
222		237
223	`; jump to end of file if flag was 0x11 (required for >> redirections)`	238	`; jump to end of file if flag was 0x11 (required for >> redirections)`
224	`cmp [REDIR_OUTAPPEND], word 0x11`	239	`cmp [REDIR_OUTAPPEND], word 0x11`
225	`jne SKIP_JMPEOF`	240	`jne SKIP_JMPEOF`
226	`mov bx, ax`	241	`mov bx, ax`
227	`mov ax, 0x4202 ; jump to position EOF - CX:DX in handle BX`	242	`mov ax, 0x4202 ; jump to position EOF - CX:DX in handle BX`
228	`xor cx, cx`	243	`xor cx, cx`
229	`xor dx, dx`	244	`xor dx, dx`
230	`int 0x21`	245	`int 0x21`
231	`mov ax, bx ; put my handle back in ax, as expected by later code`	246	`mov ax, bx ; put my handle back in ax, as expected by later code`
232	`SKIP_JMPEOF:`	247	`SKIP_JMPEOF:`
233		248
234	`; duplicate current stdout so I can revert it later`	249	`; duplicate current stdout so I can revert it later`
235	`push ax ; save my file handle in stack`	250	`push ax ; save my file handle in stack`
236	`mov ah, 0x45 ; duplicate file handle BX`	251	`mov ah, 0x45 ; duplicate file handle BX`
237	`mov bx, 1 ; 1=stdout`	252	`mov bx, 1 ; 1=stdout`
238	`int 0x21 ; ax=new (duplicated) file handle`	253	`int 0x21 ; ax=new (duplicated) file handle`
239	`mov [OLD_STDOUT], ax ; save the old handle in memory`	254	`mov [OLD_STDOUT], ax ; save the old handle in memory`
240		255
241	`; redirect stdout to my file`	256	`; redirect stdout to my file`
242	`pop bx ; dst handle`	257	`pop bx ; dst handle`
243	`mov cx, 1 ; src handle (1=stdout)`	258	`mov cx, 1 ; src handle (1=stdout)`
244	`mov ah, 0x46 ; "redirect a handle"`	259	`mov ah, 0x46 ; "redirect a handle"`
245	`int 0x21`	260	`int 0x21`
246		261
247	`; close the original file handle, I no longer need it`	262	`; close the original file handle, I no longer need it`
248	`mov ah, 0x3e ; close a file handle (handle in BX)`	263	`mov ah, 0x3e ; close a file handle (handle in BX)`
249	`int 0x21`	264	`int 0x21`
250	`NO_STDOUT_REDIR:`	265	`NO_STDOUT_REDIR:`
-		266
-		267	`; * redirect stdin if REDIR_INFIL points to something *`
-		268	`mov dx, [REDIR_INFIL]`
-		269	`cmp dx, 0xffff`
-		270	`je NO_STDIN_REDIR`
-		271	`add dx, EXECPROG ; ds:dx=file`
-		272	`mov ax, 0x3d00 ; open file for read`
-		273	`int 0x21 ; ax=handle on success (CF clear)`
-		274	`mov [REDIR_INFIL], word 0xffff`
-		275	`jc NO_STDIN_REDIR ; TODO: abort with an error message instead`
-		276
-		277	`; duplicate current stdin so I can revert it later`
-		278	`push ax ; save my file handle in stack`
-		279	`mov ah, 0x45 ; duplicate file handle BX`
-		280	`xor bx, bx ; 0=stdin`
-		281	`int 0x21 ; ax=new (duplicated) file handle`
-		282	`mov [OLD_STDIN], ax ; save the old handle in memory`
-		283
-		284	`; redirect stdout to my file`
-		285	`pop bx ; dst handle`
-		286	`xor cx, cx ; src handle (0=stdin)`
-		287	`mov ah, 0x46 ; "redirect a handle"`
-		288	`int 0x21`
-		289
-		290	`; close the original file handle, I no longer need it`
-		291	`mov ah, 0x3e ; close a file handle (handle in BX)`
-		292	`int 0x21`
-		293	`NO_STDIN_REDIR:`
251	`ret`	294	`ret`
252	`; ----------------------------------------------------------------------------`	295	`; ----------------------------------------------------------------------------`
253		296

Subversion Repositories SvarDOS

(root)/svarcom/trunk/rmod.asm – Rev 537 → 543