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_OUTFILE_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:
ret
; ----------------------------------------------------------------------------
 
 
; ----------------------------------------------------------------------------
; redirect stdout if REDIR_OUTFIL points to something
REDIR_OUTFILE_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:
ret
; ----------------------------------------------------------------------------
 

Rev 529	Rev 537
1	`;`	1	`;`
2	`; rmod - resident module of the SvarCOM command interpreter`	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`
-		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`
-		60	`; to perform normal cleanup and exit to the parent." (otherwise use iret)`
-		61	`BREAK_HANDLER: ; +F0h`
-		62	`stc`
-		63	`retf`
-		64
-		65
57	`skipsig: ; +F0h`	66	`skipsig: ; +F2h`
58		67
59	`; 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`
60	`mov ax, cs`	69	`mov ax, cs`
61	`mov ds, ax`	70	`mov ds, ax`
62	`mov es, ax`	71	`mov es, ax`
63	`mov ss, ax`	72	`mov ss, ax`
64	`mov sp, STACKPTR`	73	`mov sp, STACKPTR`
65		74
-		75	`; set up myself as break handler`
-		76	`mov ax, 0x2523 ; set int vector 23h`
-		77	`mov dx, BREAK_HANDLER`
-		78	`int 0x21`
-		79
66	`; revert stdin/stdout redirections (if any) to their initial state`	80	`; revert stdin/stdout redirections (if any) to their initial state`
67	`call REVERT_REDIR_IF_ANY`	81	`call REVERT_REDIR_IF_ANY`
68		82
69	`; redirect stdout if required`	83	`; redirect stdout if required`
70	`call REDIR_OUTFILE_IF_REQUIRED`	84	`call REDIR_OUTFILE_IF_REQUIRED`
71		85
72	`; should I executed command.com or a pre-set application?`	86	`; should I executed command.com or a pre-set application?`
73	`or [EXECPROG], byte 0`	87	`or [EXECPROG], byte 0`
74	`jz EXEC_COMMAND_COM`	88	`jz EXEC_COMMAND_COM`
75		89
76	`; 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`
77	`; int 21h, ah=50h call freezes...`	91	`; int 21h, ah=50h call freezes...`
78	`;mov ah, 0x50 ; DOS 2+ -- Set PSP`	92	`;mov ah, 0x50 ; DOS 2+ -- Set PSP`
79	`;mov bx, cs`	93	`;mov bx, cs`
80	`;int 0x21`	94	`;int 0x21`
81		95
82	`; exec an application preset (by SvarCOM) in the ExecParamRec`	96	`; exec an application preset (by SvarCOM) in the ExecParamRec`
83	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`	97	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`
84	`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)`
85	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`	99	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`
86	`int 0x21`	100	`int 0x21`
87	`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)`
88		102
89	`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)`
90		104
91	`EXEC_COMMAND_COM:`	105	`EXEC_COMMAND_COM:`
92		106
93	`; collect the exit code of previous application`	107	`; collect the exit code of previous application`
94	`mov ah, 0x4D`	108	`mov ah, 0x4D`
95	`int 0x21`	109	`int 0x21`
96	`mov [LEXCODE], al`	110	`mov [LEXCODE], al`
97		111
98	`; zero out the exec param block (14 bytes)`	112	`; zero out the exec param block (14 bytes)`
99	`mov al, 0 ; byte to write`	113	`mov al, 0 ; byte to write`
100	`mov cx, 14 ; how many times`	114	`mov cx, 14 ; how many times`
101	`mov di, EXEC_PARAM_REC ; ES:DI = destination`	115	`mov di, EXEC_PARAM_REC ; ES:DI = destination`
102	`cld ; stosb must move forward`	116	`cld ; stosb must move forward`
103	`rep stosb ; repeat cx times`	117	`rep stosb ; repeat cx times`
104		118
105	`; 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)`
106	`mov dx, COMSPECBOOT`	120	`mov dx, COMSPECBOOT`
107		121
108	`; do I have a valid COMSPEC?`	122	`; do I have a valid COMSPEC?`
109	`or [COMSPECPTR], word 0`	123	`or [COMSPECPTR], word 0`
110	`jz USEDEFAULTCOMSPEC`	124	`jz USEDEFAULTCOMSPEC`
111	`; set ES:DX to actual COMSPEC (in env segment)`	125	`; set ES:DX to actual COMSPEC (in env segment)`
112	`mov es, [PSP_ENVSEG]`	126	`mov es, [PSP_ENVSEG]`
113	`mov dx, [COMSPECPTR]`	127	`mov dx, [COMSPECPTR]`
114	`USEDEFAULTCOMSPEC:`	128	`USEDEFAULTCOMSPEC:`
115		129
116	`; prepare the exec param block`	130	`; prepare the exec param block`
117	`mov ax, [PSP_ENVSEG]`	131	`mov ax, [PSP_ENVSEG]`
118	`mov [EXEC_PARAM_REC], ax`	132	`mov [EXEC_PARAM_REC], ax`
119	`mov [EXEC_PARAM_REC+2], word CMDTAIL`	133	`mov [EXEC_PARAM_REC+2], word CMDTAIL`
120	`mov [EXEC_PARAM_REC+4], cs`	134	`mov [EXEC_PARAM_REC+4], cs`
121		135
122	`; execute command.com`	136	`; execute command.com`
123	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`	137	`mov ax, 0x4B00 ; DOS 2+ - load & execute program`
124	`push es ;`	138	`push es ;`
125	`pop ds ;`	139	`pop ds ;`
126	`;mov dx, COMSPEC ; DS:DX - ASCIZ program name (preset already)`	140	`;mov dx, COMSPEC ; DS:DX - ASCIZ program name (preset already)`
127	`push cs`	141	`push cs`
128	`pop es`	142	`pop es`
129	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`	143	`mov bx, EXEC_PARAM_REC ; ES:BX - parameter block pointer`
130	`int 0x21`	144	`int 0x21`
131		145
132	`; if all went well, jump back to start`	146	`; if all went well, jump back to start`
133	`jnc skipsig`	147	`jnc skipsig`
134		148
135	`; restore DS=CS`	149	`; restore DS=CS`
136	`mov bx, cs`	150	`mov bx, cs`
137	`mov ds, bx`	151	`mov ds, bx`
138		152
139	`; update error string so it contains the error number`	153	`; update error string so it contains the error number`
140	`add al, '0'`	154	`add al, '0'`
141	`mov [ERRLOAD + 4], al`	155	`mov [ERRLOAD + 4], al`
142		156
143	`; display error message`	157	`; display error message`
144	`mov ah, 0x09`	158	`mov ah, 0x09`
145	`mov dx, ERRLOAD`	159	`mov dx, ERRLOAD`
146	`int 0x21`	160	`int 0x21`
147		161
148	`; wait for keypress`	162	`; wait for keypress`
149	`mov ah, 0x08`	163	`mov ah, 0x08`
150	`int 0x21`	164	`int 0x21`
151		165
152	`; back to program start`	166	`; back to program start`
153	`jmp skipsig`	167	`jmp skipsig`
154		168
155	`; 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`
156	`; 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`
157	`; 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)`
158	`; this allows multiple copies of SvarCOM to stack upon each other.`	172	`; this allows multiple copies of SvarCOM to stack upon each other.`
159	`CMDTAIL db 0x01, 0x0A, 0x0D`	173	`CMDTAIL db 0x01, 0x0A, 0x0D`
160		174
161	`ERRLOAD db "ERR x, FAILED TO LOAD COMMAND.COM", 13, 10, '$'`	175	`ERRLOAD db "ERR x, FAILED TO LOAD COMMAND.COM", 13, 10, '$'`
162		176
163	`; variables used to revert stdin/stdout to their initial state`	177	`; variables used to revert stdin/stdout to their initial state`
164	`OLD_STDOUT dw 0xffff`	178	`OLD_STDOUT dw 0xffff`
165	`OLD_STDIN dw 0xffff`	179	`OLD_STDIN dw 0xffff`
166		180
167		181
168	`; ****************************************************************************`	182	`; ****************************************************************************`
169	`; * ROUTINES *************************************************************`	183	`; * ROUTINES *************************************************************`
170	`; ****************************************************************************`	184	`; ****************************************************************************`
171		185
172	`; ----------------------------------------------------------------------------`	186	`; ----------------------------------------------------------------------------`
173	`; revert stdin/stdout redirections (if any) to their initial state`	187	`; revert stdin/stdout redirections (if any) to their initial state`
174	`; 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`
175	`; times when DS is out of whack.`	189	`; times when DS is out of whack.`
176	`REVERT_REDIR_IF_ANY:`	190	`REVERT_REDIR_IF_ANY:`
177	`; is stdout redirected?`	191	`; is stdout redirected?`
178	`mov bx, [OLD_STDOUT]`	192	`mov bx, [OLD_STDOUT]`
179	`cmp bx, 0xffff`	193	`cmp bx, 0xffff`
180	`je STDOUT_DONE`	194	`je STDOUT_DONE`
181	`; revert the stdout handle (dst in BX already)`	195	`; revert the stdout handle (dst in BX already)`
182	`mov cx, 1 ; src handle (1=stdout)`	196	`mov cx, 1 ; src handle (1=stdout)`
183	`mov ah, 0x46 ; redirect a handle`	197	`mov ah, 0x46 ; redirect a handle`
184	`int 0x21`	198	`int 0x21`
185	`; close the old handle (still in bx)`	199	`; close the old handle (still in bx)`
186	`mov ah, 0x3e`	200	`mov ah, 0x3e`
187	`int 0x21`	201	`int 0x21`
188	`mov [OLD_STDOUT], word 0xffff ; mark stdout as "not redirected"`	202	`mov [OLD_STDOUT], word 0xffff ; mark stdout as "not redirected"`
189	`STDOUT_DONE:`	203	`STDOUT_DONE:`
190	`ret`	204	`ret`
191	`; ----------------------------------------------------------------------------`	205	`; ----------------------------------------------------------------------------`
192		206
193		207
194	`; ----------------------------------------------------------------------------`	208	`; ----------------------------------------------------------------------------`
195	`; redirect stdout if REDIR_OUTFIL points to something`	209	`; redirect stdout if REDIR_OUTFIL points to something`
196	`REDIR_OUTFILE_IF_REQUIRED:`	210	`REDIR_OUTFILE_IF_REQUIRED:`
197	`mov si, [REDIR_OUTFIL]`	211	`mov si, [REDIR_OUTFIL]`
198	`cmp si, 0xffff`	212	`cmp si, 0xffff`
199	`je NO_STDOUT_REDIR`	213	`je NO_STDOUT_REDIR`
200	`add si, EXECPROG ; si=output file`	214	`add si, EXECPROG ; si=output file`
201	`mov ax, 0x6c00 ; Extended Open/Create`	215	`mov ax, 0x6c00 ; Extended Open/Create`
202	`mov bx, 1 ; access mode (0=read, 1=write, 2=r+w)`	216	`mov bx, 1 ; access mode (0=read, 1=write, 2=r+w)`
203	`xor cx, cx ; file attribs when(if) file is created (0=normal)`	217	`xor cx, cx ; file attribs when(if) file is created (0=normal)`
204	`mov dx, [REDIR_OUTAPPEND] ; action if file exist (0x11=open, 0x12=truncate)`	218	`mov dx, [REDIR_OUTAPPEND] ; action if file exist (0x11=open, 0x12=truncate)`
205	`int 0x21 ; ax=handle on success (CF clear)`	219	`int 0x21 ; ax=handle on success (CF clear)`
206	`mov [REDIR_OUTFIL], word 0xffff`	220	`mov [REDIR_OUTFIL], word 0xffff`
207	`jc NO_STDOUT_REDIR ; TODO: abort with an error message instead`	221	`jc NO_STDOUT_REDIR ; TODO: abort with an error message instead`
208		222
209	`; jump to end of file if flag was 0x11 (required for >> redirections)`	223	`; jump to end of file if flag was 0x11 (required for >> redirections)`
210	`cmp [REDIR_OUTAPPEND], word 0x11`	224	`cmp [REDIR_OUTAPPEND], word 0x11`
211	`jne SKIP_JMPEOF`	225	`jne SKIP_JMPEOF`
212	`mov bx, ax`	226	`mov bx, ax`
213	`mov ax, 0x4202 ; jump to position EOF - CX:DX in handle BX`	227	`mov ax, 0x4202 ; jump to position EOF - CX:DX in handle BX`
214	`xor cx, cx`	228	`xor cx, cx`
215	`xor dx, dx`	229	`xor dx, dx`
216	`int 0x21`	230	`int 0x21`
217	`mov ax, bx ; put my handle back in ax, as expected by later code`	231	`mov ax, bx ; put my handle back in ax, as expected by later code`
218	`SKIP_JMPEOF:`	232	`SKIP_JMPEOF:`
219		233
220	`; duplicate current stdout so I can revert it later`	234	`; duplicate current stdout so I can revert it later`
221	`push ax ; save my file handle in stack`	235	`push ax ; save my file handle in stack`
222	`mov ah, 0x45 ; duplicate file handle BX`	236	`mov ah, 0x45 ; duplicate file handle BX`
223	`mov bx, 1 ; 1=stdout`	237	`mov bx, 1 ; 1=stdout`
224	`int 0x21 ; ax=new (duplicated) file handle`	238	`int 0x21 ; ax=new (duplicated) file handle`
225	`mov [OLD_STDOUT], ax ; save the old handle in memory`	239	`mov [OLD_STDOUT], ax ; save the old handle in memory`
226		240
227	`; redirect stdout to my file`	241	`; redirect stdout to my file`
228	`pop bx ; dst handle`	242	`pop bx ; dst handle`
229	`mov cx, 1 ; src handle (1=stdout)`	243	`mov cx, 1 ; src handle (1=stdout)`
230	`mov ah, 0x46 ; "redirect a handle"`	244	`mov ah, 0x46 ; "redirect a handle"`
231	`int 0x21`	245	`int 0x21`
232		246
233	`; close the original file handle, I no longer need it`	247	`; close the original file handle, I no longer need it`
234	`mov ah, 0x3e ; close a file handle (handle in BX)`	248	`mov ah, 0x3e ; close a file handle (handle in BX)`
235	`int 0x21`	249	`int 0x21`
236	`NO_STDOUT_REDIR:`	250	`NO_STDOUT_REDIR:`
237	`ret`	251	`ret`
238	`; ----------------------------------------------------------------------------`	252	`; ----------------------------------------------------------------------------`
239		253

Subversion Repositories SvarDOS

(root)/svarcom/trunk/rmod.asm – Rev 529 → 537