[英]How to execute DOS' COMMAND.COM command from FASM?
Is there any DOS function to execute string, containing command.com's line?是否有任何 DOS function 执行字符串,包含 command.com 的行? I need something like C's
system()
, but for DOS and FASM.我需要类似 C 的
system()
之类的东西,但适用于 DOS 和 FASM。
I've previously used code like this to execute DOS shell commands.我以前使用过这样的代码来执行 DOS shell 命令。 It's for nasm, but you might be able to adapt it for your purposes.
它适用于 nasm,但您可以根据自己的目的对其进行调整。 This code specifically executes our own command line tail as a DOS command, but you can patch in some other command line tail if you want to execute a different command.
这段代码专门将我们自己的命令行尾部作为 DOS 命令执行,但如果您想执行不同的命令,可以修补其他一些命令行尾部。
section .data
comspec db "COMSPEC=" ; for finding COMSPEC in the env block
comlen equ $-comspec
command db "COMMAND.COM",0
; EXEC parameter block
execpar dw 0 ; environment for child (use ours)
dw 80h, 0h ; command tail (use ours)
dw 5Ch, 0h ; first FCB (use ours)
dw 6Ch, 0h ; second FCB (use ours)
section .text
; execute DOS command
doexec:
mov bx, execpar ; EXEC parameter block
mov [bx+4], cs ; fix up segment for command tail
mov [bx+8], cs ; fix up segment for first FCB
mov [bx+12], cs ; fix up segment for second FCB
call fndcom ; write pointer to COMSPEC value to DS:SI
mov dx, si
mov ax, 4B00h ; LOAD AND EXECUTE PROGRAM
int 21h
jnc .ok ; error occured?
push ax ; remember error code
call fndcom ; find COMSPEC value anew
pop ax ; restore error code
call perror ; print error message
.ok: push cs ; restore ds
pop ds
ret
; find COMSPEC in the environment block
; and load pointer to it to DS:SI
; preserves bx
fndcom: mov ds, [2Ch] ; environment block
xor si, si ; beginning of env block
; loop invariant: si points to the beginning of
; a string in the environment
.loop1: cmp byte [si], 0 ; end of environment reached?
je .nope
mov di, comspec ; find "COMSPEC="
mov cx, comlen ;
repe cmpsb ; compare strings
je .found ; if found, we are done
dec si ; go back to mismatched character
.loop2: lodsb ; search si for end of string
test al, al ; end of string reached?
jne .loop2 ; nope
jmp .loop1 ; check next string in environment
; COMSPEC unset
.nope: push cs
pop ds ; restore ds
mov si, command ; "COMMAND.COM"
ret
; COMSPEC found
.found: ret
The basic idea is to find the name of the command interpreter by searching for a variable named COMSPEC
in the environment block.基本思想是通过在环境块中搜索一个名为
COMSPEC
的变量来找到命令解释器的名称。 If none is found, we default to COMMAND.COM
.如果没有找到,我们默认为
COMMAND.COM
。 Then, we build an exec parameter block with useful details for the program we would like to execute, including the command line.然后,我们构建一个exec 参数块,其中包含我们想要执行的程序的有用详细信息,包括命令行。 This is where you need to put the shell command to be executed (in the format of a command line tail).
这是您需要放置要执行的 shell 命令的地方(以命令行尾部的格式)。 Finally, we invoke DOS function 4b00: execute program to execute the command interpreter, running our command.
最后,我们调用DOS function 4b00:执行程序来执行命令解释器,运行我们的命令。
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