I need to create an executable from the next assembly code:
.MODEL SMALL
.DATA
TEXT DB 'Hello world!$'
.CODE
.STACK 20
.STARTUP
MOV AX, #DATA
MOV DS, AX
MOV AH, 9
MOV BL, 02H
INT 10H
MOV Dx, OFFSET TEXT
INT 21H
MOV AH, 4CH
INT 21H
END
It works with Turbo Assembler (tasm.exe), but I don't want to continue working with it, because it doesn't run in Windows 7.
Thanks.
If there is an ongoing need to develop MSDOS programs, run a 16-bit environment like DOSBOX. That way tasm.exe—one of the finest assemblers of its day—can also run, along with your program, and the tools that go with tasm—Turbo Debugger, Turbo Linker, and Turbo C.
You could also install Windows XP or Windows 98 over Windows 7, as a multi-boot alongside it, or in a virtual machine hosted by Windows 7. Either way, you'd then have the ability to run MSDOS programs without hassle.
As Greg Hewgill mentioned, major rearchitecting of the program is needed for it to run in a 32-bit (or greater) environment.
use Microsoft macro assembler (MASM)
You could try NASM or MASM, but your source will likely need minor changes to work with those.
Your code as given is suitable for 16-bit DOS systems. To use a modern assembler, you will have to modify your code to work in a 32-bit environment, which may be a nontrivial process. All the code you've given so far will need to be rewritten.
I recommend NASM as it is an active, well supported project.
GNU Assembler
Related
So i installed a kernel driver on my windows machine but accidentally left a while(1) in there (I know pretty stupid) and now OS just hangs when i start it. Is there a way to revert the driver to an earlier stage or revert to "previous commit" like we do in git? i can see thought WinDbg that it just hangs there. Even though i can break into it I can't seem to make it move on from that infinite loop.
you'd typically have the below assembly controlling the while(1) loop. From inside the debugger change to assembly source mode and then alter rax register from 0 to 1. That should branch out the subsequent je.
xor eax,eax
cmp eax,1
je xyz
Generally, you'd have to change the driver's start type to "disabled" and fix up other registry entries if it is a filter to any other boot critical devices (eg upper/lower filter)
I am taking Assembly this semester. I am trying to use DumpRegs to display my registers, however, I get an error when running without debugging. The program builds (successfully it says), hangs and then my cmd prompt displays: "The system cannot execute the specified program."
If I debug, Visual Studio says "Insufficient resources exist to complete the requested service", then my antivirus attempts to quarantine "Generic RX BM-OC!257C1442E357 " at the time of running. I just ran a scan and I have no viruses, only downloads have been the Irvine library off of his site earlier today. Any ideas? I'm on a 64 bit machine, but their site said it was tested for 32 bit and 64 bit machines.
Here is the incredibly simple code:
include Irvine32.inc
.code
main PROC
mov eax,5
add eax,6
call DumpRegs
exit
main ENDP
END main
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I really need some help here. I've been searching online for about 2 days now and can't seem to find an answer to the problems that I got.
I downloaded nasm and installed it it seems to work but I can't seem to find any example code that works on windows 64bit (it would be awesome if you could make a simple hello world example for me or something).
(And how to compile it)
How would I turn the .o file into a .exe?
How would I accesses the screen or gpu memory (I think) to print stuff on the screen (like some sort of console application)?
There a a few things to consider when programming in assembly using NASM under Windows:
NASM is just an assembler
A linker is needed to create an executable.
Windows API are implemented as a user space library.
The library is not entirely in user space, some functions cross the boundary, but the interface to the application is a set of DLL, most notably: kernel32.dll, user32.dll and so on.
Windows' executables can have different subsystems.
Among the others the IMAGE_SUBSYSTEM_WINDOWS_GUI and IMAGE_SUBSYSTEM_WINDOWS_CUI are the most used, the former being used by applications that create windows and the latter by applications that use a console1.
The linker takes to COFF object (.obj) file generated by the assembler, takes a set of library definitions (.lib) and perform these important steps:
It resolves the call to external functions found in the object file.
A function marked as external is meant to be found in one of the library definition, the linker then fixes the call instruction to point to a location where the address of the function will be found at run-time.
It add the dependency libraries to the final executable.
This is done with the help of the PE file format, basically if F if found on the library L then L is added to the dependencies list along with a location where to write the address of F.
The loader will do the rest.
The linking is actually more complex than that.
It is also responsible for setting the various PE flags and settings, including the subsytem and the entrypoint.
To write an executable using NASM with need:
A linker.
The set of library definitions.
These can be found in the Windows SDK2.
The linker we will use in this example is the Microsoft LINK linker.
As #CodyGray pointed out in its comment (quoting because I'm lazy):
The Windows 7 version of the SDK that you linked does include all of the build tools. The Windows 8 SDK changed and no longer ships with the command-line build tools, forcing you to download a Visual Studio package
Once we have the tools, we can start programming.
We will use WriteFile to write a string to the standard output (like we would in Linux assembly).
The handler to the standard output must be retrieved with GetStdHandle though.
In Windows you can exit a process with a ret even with no CRT (C run-time) linked (i.e. in a bare process).
I won't explain the Window 64 ABI nor the trickery of programming in 64-bit.
BITS 64
DEFAULT REL ;RIP relative addressing by default
GLOBAL main ;Main must be visible to the linker
;Function the linker will look for in other modules (libs or objs)
EXTERN WriteFile
EXTERN GetStdHandle
STD_OUTPUT_HANDLE EQU -11
SECTION .data
strHelloWorld db "Hello world!", 13, 10, 0
lenHelloWorld dd $-strHelloWorld
hOut dd 0 ;Will store STDOUT handler
SECTION .text
main:
sub rsp, 30h ;20h (Home space) + 10h (params)
;Get STDOUT handler (Handler are 32-bit values)
mov ecx, STD_OUTPUT_HANDLE
call GetStdHandle
mov DWORD [hOut], eax ;Useless as now, for future reuse
;Write strHelloWorld to STDOUT
mov ecx, eax
lea rdx, [strHelloWorld]
mov r8d, DWORD [lenHelloWorld]
xor r9, r9
mov QWORD [rsp+20h], r9
call WriteFile
add rsp, 30h
ret
To create an executable from this source, we first assemble it into a 64-bit object file:
nasm -fwin64 hello.asm -o hello.obj
then we link it against the kernel32 library (the only one we need):
link /MACHINE:X64 /SUBSYSTEM:CONSOLE /OUT:hello.exe /NODEFAULTLIB /ENTRY:main kernel32.lib hello.obj
the CLI switches are pretty straightforward, NODEFAULTLIB avoid linking with MSVCVRXX.lib, the Microsoft CRT.
Those are the minimal switches necessary to build an executable in this example.
I assume you are smart enough to fix the path issues when issuing the commands above, particularly you can tell link where to find the lib files.
For this example I just copied them from the SDK installation folder.
As proposed in other answers, you can use other assemblers that may came with a linker.
Another possible developing environment is to use gcc (either inside cygwin or as mingw) to perform the linker step.
1 In this case Windows automatically create a console for the application and set the standard handlers appropriately. GUI application can recreate the console too (or more than one), so IMAGE_SUBSYSTEM_WINDOWS_GUI must be intended as "No console by default".
2 The version linked is the first Google result, invest more time in finding a suitable version. Also, I'm not sure if there is a linker in the Windows SDK or you need to download a Visual Studio instead.
Download Flat Assembler.(Download->flat assembler for windows)
http://flatassembler.net/
Extract zip.
Goto 'examples/win64/pe64demo/'
open 'pe64demo.exe'
(source code is in 'pe64demo.asm')
I found a guide how to bypass it in ollydbg:
see here
But how to do that for an x64 application?
I have found following:
How must i manipulate this to don't get it detect the debugger?
You can do it the same way as described in the guide (i.e. by patching the code of IsDebuggerPresent).
Or you can set a breakpoint at the "movzx eax, byte ptr ds:[rax+2]" instruction, and when the program stops at the breakpoint, go to RAX+2 in the Dump pane and then change the byte from 1 to 0.
I am trying to learn assembly language in my spare time to help me in my role as a developer using high level languages.
I have followed the NASM tutorial here: http://leto.net/writing/nasm.php.
I am able to create and run a simple program that prints HelloWorld to the screen. I am confused by the following paragraph in the link above:
mov eax,5 ; the syscall number for open()
So where do find out all of the semantics for all of the various system calls?
Well first, the numbers are listed in asm/unistd.h in Linux, and sys/syscall.h
in the *BSD's
I assume that this means that: if there is a 5 in the eax register, then it is a system call for open. Are the rest of the system calls documented somewhere?
I am using NASM on a Windows 7 PC.
List of Windows API calls
If and when you use NASM on Linux,
http://asm.sourceforge.net/syscall.html#1
http://syscalls.kernelgrok.com/