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  • Getting Started with NASM

    - by MarkPearl
    Today I got to play with NASM. This is an assembler and disassembler that can be used to write 16-bit, 32-bit & 64-bit programs. Let me say upfront that the last time I looked at assembly code at any depth was when I was studying Computer Science in Pietermaritzburg – ten years ago – and we never ever got to touch any real assembly code so a lot of what I am looking at today is very new to me. The first thing I did was download NASM compiler. This turned out to be a bit more complicated than I thought. Originally I went to http://www.nasm.us/ and downloaded the nasm-2.09.04.zip file which I thought had all I needed. No luck! It seemed to just have the uncompiled code, and from what I could tell I would need to recompile and build it – possibly in c++? Well, I wasn’t going to waste my time with that, so a bit more searching and I found the Win32 (http://www.nasm.us/pub/nasm/releasebuilds/2.09.04/win32/) folder Nasm.exe which I downloaded. Choosing an IDE So, I have NASM compiler but to compile anything you need to pass a string of special characters in the command prompt. That’s fine if I was going to just do one program once every couple of years, but since I am aiming to do quite a bit more exploration of NASM I began searching for an IDE. There were a few options, even apparently Visual Studio with a bit of tweeking could do the job, but from past experience I wanted to avoid the VS route as it can sometimes get confusing. I eventually settled on TextPad which I had used a few years ago for a similar project and it had been simple enough yet powerful enough to do the job. A bit of searching and I found a syntax file for NASM and everything seemed hunky dory. Configuring TextPad to run the NASM Compiler Next was to get TextPad to run the NASM compiler. TextPad has this external tools option that allows one to configure special commands. To simplify the process I first created a bat file in the NASM directory that allowed me to simply compile asm files. The bat file was called as.bat and had just one line of code… nasm -f bin %1.asm -o %1.com -l %1.lst Once I had created as.bat I just needed to go into TextPad and create a tool. I have made a quick video of that just showing you where the various settings are which is viewable below. The 64Bit Problem So I now have an ‘IDE’ linked to my NASM compiler so everything should be fine right? No! Whenever I tried to compile an asm program it compiles fine, but when I try and run it I get an error – “This version of the file is not compatible with the version Windows you’re running. Check your computer’s system information to see whether you need an x86 (32-bit) or x64 (64-bit) version of the program, and then contact the software publisher." Well.. it turns out there are a few complications with having a 64 bit OS! So after searching google and coming to any real solution that I could find other than perhaps attempting to build the code for nasm, I eventually resorted to running a VM with Windows XP on it and putting NASM there… My first hello world program So I attempt my first hello world program as per an example I found… the code was quite simple and is shown below… bits16 org 0x100 jmp main message: db 'Hello World',0ah,0dh,'$' main: mov dx,message mov ah,09 int 21h int 20h Running the build tool from TextPad and everything compiles fine and I now have a console app with helllo world shown. Conclusion It’s very early days with NASM. I have been spoilt with Visual Studio and high order languages so I assume it will be a painful ride getting into the basics of assembly programming but I am hoping that at the end of it, I will at least have a bit more exposure to a language closer to the metal.

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  • link nasm program for mac os x

    - by Fry Constantine
    i have some problems with linking nasm program for macos: GLOBAL _start SEGMENT .text _start: mov ax, 5 mov bx, ax mov [a], ebx SEGMENT .data a DW 0 t2 DW 0 fry$ nasm -f elf test.asm fry$ ld -o test test.o -arch i386 ld: warning: in test.o, file was built for unsupported file format which is not the architecture being linked (i386) ld: could not find entry point "start" (perhaps missing crt1. fry$ nasm -f macho test.asm fry$ ld -o test test.o -arch i386 ld: could not find entry point "start" (perhaps missing crt1.o) can anyone help me?

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  • [NASM] How do I print out the content of a register in Hex

    - by Johnny ASM
    Hi, I'm currently getting started with NASM and wanted to know, how to output the contents of a register with NASM in Hexadecimal. I can output the content of eax with section .bss reg_buf: resb 4 . . . print_register: mov [reg_buf], eax mov eax, SYS_WRITE mov ebx, SYS_OUT mov ecx, reg_buf mov edx, 4 int 80h ret Let's say eax contains 0x44444444 then the output would be "DDDD". Apparently each pair of "44" is interpreted as 'D'. My ASCII table approves this. But how do I get my program to output the actual register content (0x44444444)?

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  • Am I Writing Assembly Or NASM?

    - by cam
    I'm fed up with this. I've been trying to just get a grip on assembly for awhile, but I feel like I'm coding towards my compiler rather than a language. I've been using this tutorial, and so far it's giving me hell. I'm using NASM, which may be the problem, but I figured it was the most popular one. I'm simply trying to learn the most general form of assembly, so I decided to learn x86. I keep running into stupid errors, like not being able to increment a variable. Here's the latest one: not being able to use div. mov bx, 0; mov cx, 0; jmp start; start: inc cx; mov ax, cx; div 3; <-- invalid combination of opcode and operand cmp ah,0; jz totalvalue; mov ax, cx; div 5; <-- invalid combination of opcode and operand cmp ah, 0; jz totalvalue; cmp cx, 1000; jz end; totalvalue: add bx,cx; jmp start; jmp end; end: mov ah,4ch; mov al,00; int 21h; Should I change compilers? It seems like division should be standard. Do I need to read two tutorials (one on NASM, and one on x86?). Any specific help on this problem?

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  • nasm infinite loop with FPU

    - by Ben Ishak
    i'm trying to create a small nasm program which do this operation in floating point while(input <= 10^5) do begin input = input * 10 i = i - 1 end the equivilant program in nasm is as following section .data input: resd 1 n10: dd 0x41200000 ; 10 _start: mov eax, 200 ; eax = 200 ; extract eax -> Floating Point IEEE 754 and eax, 0x7f800000 shr eax, 23 sub eax, 127 mov dword [input], eax ; input = eax = 200 mov edx, 0x49742400 ; 10^5 ; %begin mov ecx, 0 ; i = 0 jmp alpha alpha: fld dword [input] cmp [input], edx ; input <= 10^5 jle _while jmp log2 _while: fld dword [n10] ; 10 fld dword [input] ; input fmul st0, st1 ; input * 10 fst dword [input] ; input = input dec ecx ; i = i - 1 jmp alpha the _while loop is iterating infinitely ecx / i gards always the same value = -4194304 (it is sepposed to be 0) and doesn't decrement

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  • Writing an OS kernel in assembly with NASM

    - by Betamoo
    I want to know what is the standard way for writing a -simple- kernel to be compiled on NASM? To get it clearer: I was able to define the code block with all the following ways: [segment code] [segment .code] segment code segment .code [section code] [section .code] section code section .code I need to know what is the standard way to do that, And what is the difference between them... Thanks

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  • What are the limitations of assembler? (NASM)

    - by citronas
    Is there a technical limitation of what kind of programs I can write with assembler (NASM)? For now I've only seem some program that do arithmetic operations, like adding two numbers. Is it possible to write complex assembler programs, that provide a GUI, access the file system, plays sounds et cetera? I know I wouldn't write such programs, but I'm curious, if there are technical limitations on what kind of programs I can write with assembler.

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  • nasm/yasm arguments, linkage to C++

    - by arionik
    Hello everybody, I've got a question concerning nasm and its linkage to C++. I declare a litte test function as extern "C" void __cdecl myTest( byte i1, byte i2, int stride, int *width ); and I call it like this: byte i1 = 1, i2 = 2; int stride = 3, width = 4; myTest( i1, i2, stride, &width ); the method only serves to debug assembly and have a look at how the stack pointer is used to get the arguments. beyond that, the pointer arguments value shall be set to 7, to figure out how that works. This is implemented like this: global _myTest _myTest: mov eax, [esp+4] ; 1 mov ebx, [esp+8] ; 2 mov ecx, dword [esp+16] ; width mov edx, dword [esp+12] ; stride mov eax, dword [esp+16] mov dword [eax], 7 ret and compiled via yasm -f win32 -g cv8 -m x86 -o "$(IntDir)\$(InputName).obj" "$(InputPath)" , then linked to the c++ app. In debug mode, everything works fine. the function is called a couple of times and works as expected, whereas in release mode the function works once, but subsequent programm operations fail. It seems to me that something's wrong with stack/frame pointers, near/far, but I'm quite new to this subject and need a little help. thanks in advance! a.

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  • NASM - Load code from USB Drive

    - by new123456
    Hola, Would any assembly gurus know the argument (register dl) that signifies the first USB drive? I'm working through a couple of NASM tutorials, and would like to get a physical boot (I can get a clean one with qemu). This is the section of code that loads the "kernel" data from disk: loadkernel: mov si, LMSG ;; 'Loading kernel',13,10,0 call prints ;; ex puts() mov dl, 0x00 ;; The disk to load from mov ah, 0x02 ;; Read operation mov al, 0x01 ;; Sectors to read mov ch, 0x00 ;; Track mov cl, 0x02 ;; Sector mov dh, 0x00 ;; Head mov bx, 0x2000 ;; Buffer end mov es, bx mov bx, 0x0000 ;; Buffer start int 0x13 jc loadkernel mov ax, 0x2000 mov ds, ax jmp 0x2000:0x00 If it makes any difference, I'm running a stock Dell Inspiron 15 BIOS. Apparently, the correct value for me is 0x80. The BIOS loads the hard drives and labels them starting at 0x80 according to this answer. My particular BIOS decides to load the USB drive up as the first, for some reason, so I can boot from there.

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  • Problem in linking an nasm code

    - by Stefano
    I'm using a computer with an Intel Core 2 CPU and 2GB of RAM. The SO is Ubuntu 9.04. When I try to compile this code: ;programma per la simulazione di un terminale su PC, ottenuto utilizzando l'8250 ;in condizione di loopback , cioè Tx=Rx section .code64 section .data TXDATA EQU 03F8H ;TRASMETTITORE RXDATA EQU 03F8H ;RICEVITORE BAUDLSB EQU 03F8H ;DIVISORE DI BAUD RATE IN LSB BAUDMSB EQU 03F9H ;DIVISORE DI BAUD RATE IN MSB INTENABLE EQU 03F9H ;REGISTRO DI ABILITAZIONE DELL'INTERRUZIONE INTIDENTIF EQU 03FAH ;REGISTRO DI IDENTIFICAZIONE DELL'INTERRUZIONE LINECTRL EQU 03FBH ;REGISTRO DI CONTROLLO DELLA LINEA MODEMCTRL EQU 03FCH ;REGISTRO DI CONTROLLO DEL MODEM LINESTATUS EQU 03FDH ;REGISTRO DI STATO DELLA LINEA MODEMSTATUS EQU 03FEH ;REGISTRO DI STATO DEL MODEM BAUDRATEDIV DW 0060H ;DIVISOR: LOW=60, HIGH=00 -BAUD =9600 COUNTERCHAR DB 0 ;CHARACTER COUNTER ;DW 256 DUP (?) section .text global _start _start: ;PROGRAMMAZIONE 8250 MOV DX,LINECTRL MOV AL,80H ;BIT 7=1 PER INDIRIZZARE IL BAUD RATE OUT DX,AL MOV DX,BAUDLSB MOV AX,BAUDRATEDIV ;DEFINISCO FATTORE DI DIVISIONE OUT DX,AL MOV DX,BAUDMSB MOV AL,AH OUT DX,AL ;MSB MOV DX,LINECTRL MOV AL,00000011B ;8 BIT DATO, 1 STOP, PARITA' NO OUT DX,AL MOV DX,MODEMCTRL MOV AL,00010011B ;BIT 4=0 PER NO LOOPBACK OUT DX,AL MOV DX,INTENABLE XOR AL,AL ;DISABILITO TUTTI GLI INTERRUPTS OUT DX,AL CICLO: MOV DX,LINESTATUS IN AL,DX ;LEGGO IL REGISTRO DI STATO DELLA LINEA TEST AL,00011110B ;VERIFICO GLI ERRORI (4 TIPI) JNE ERRORI TEST AL,01H ;VERIFICO Rx PRONTO JNE LEGGOCHAR TEST AL,20H ;VERIFICO Tx VUOTO JE CICLO ;SE SI ARRIVA A QUESTO PUNTO ALLORA L'8250 è PRONTO PER TRASMETTERE UN NUOVO CARATTERE MOV AH,1 INT 80H JE CICLO ;SE SI ARRIVA A QUESTO PUNTO SIGNIFICA CHE ESISTE UN CARATTERE DA TASTIERA MOV AH,0 INT 80H ;Al CONTIENE IL CARATTERE DELLA TASTIERA MOV DX,3F8H OUT DX,AL JMP CICLO LEGGOCHAR: MOV AL,[COUNTERCHAR] INC AL CMP AL,15 JE FINE MOV [COUNTERCHAR],AL MOV DX,TXDATA IN AL,DX ;AL CONTIENE IL CARATTERE RICEVUTO AND AL,7FH ;POICHè VI SONO 7 BIT DI DATO ;VISUALIZZAZIONE DEL CARATTERE MOV BX,0 MOV AH,14 INT 80H POP AX CMP AL,0DH ;CONTROLLO SE RETURN JNE CICLO ;CAMBIO RIGA DI VISUALIZZAZIONE MOV AL,0AH MOV BX,0 MOV AH,14 ;INT 10H INT 80H JMP CICLO ;GESTIONE ERRORI ERRORI: MOV DX,3F8H IN AL,DX MOV AL,'?' MOV BX,0 MOV AH,14 INT 80H JMP CICLO FINE: XOR AH,AH MOV AL,03 INT 80H When I compile this code "NASM -f bin UARTLOOP.asm", the compiler can create the UARTLOOP.o file without any error. When I try to link the .o file with "ld UARTLOOP.o" it tells: UARTLOOP.o: In function `_start': UARTLOOP.asm:(.text+0xd): relocation truncated to fit: R_X86_64_16 against `.data' Have u got some ideas to solve this problem? Thx =)

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  • More NASM with GVim

    - by MarkPearl
    Today I am bashing around with nasm again… some useful things I found… Set the current working directory of gvim to the current file path I have found setting the current working directory of gvim to the file location is very useful, especially if you are wanting to use commands in gvim to run your compiled code. It can be done by typing in the following in the command mode in gvim… cd %:p:h Once you have set it, you can use the ! to run commands you would normally run in the dos shell.. e.g. !dir Compiling code to make an executable There are three thing you need to specify to compile a basic file in name, they are… The output file format The output file name The source file name An example of this would be the following (where you have a file called temp.asm which is the source file) nasm –f bin temp.asm –o temp.com Output file format The –f specifies the output file format (in this case a binary file). To get a list of the available output file formats you can type nasm –hf (for my installation bin is the default, in which case I can omit it) Output file name This is just the name you want the compiled file to be called. For windows machines I specify .com as my default format.

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  • Problem with asm program (nasm)

    - by GLeBaTi
    org 0x100 SEGMENT .CODE mov ah,0x9 mov dx, Msg1 int 0x21 ;string input mov ah,0xA mov dx,buff int 0x21 mov ax,0 mov al,[buff+1]; length ;string UPPERCASE mov cl, al mov si, buff cld loop1: lodsb; cmp al, 'a' jnb upper loop loop1 ;output mov ah,0x9 mov dx, buff int 0x21 exit: mov ah, 0x8 int 0x21 int 0x20 upper: sub al,32 jmp loop1 SEGMENT .DATA Msg1 db 'Press string: $' buff db 254,0 this code perform poorly. I think that problem in "jnb upper". This program make small symbols into big symbols.

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  • easy asm program(nasm)

    - by GLeBaTi
    org 0x100 SEGMENT .CODE mov ah,0x9 mov dx, Msg1 int 0x21 ;string input mov ah,0xA mov dx,buff int 0x21 mov ax,0 mov al,[buff+1]; length ;string UPPERCASE mov cl, al mov si, buff cld loop1: lodsb; cmp al, 'a' jnb upper loop loop1 ;output mov ah,0x9 mov dx, buff int 0x21 exit: mov ah, 0x8 int 0x21 int 0x20 upper: sub al,32 jmp loop1 SEGMENT .DATA Msg1 db 'Press string: $' buff db 254,0 this code perform poorly. I think that problem in "jnb upper". This program make small symbols into big symbols.

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  • writing to a file in nasm using system calls

    - by yurib
    As part of an assignment I'm supposed to write to a file using system calls. Everything works fine except when I try to open the file in gedit (linux), it says it can't identify the character encoding. Notepad (on windows) opens the file just fine. Why doesn't it work on linux ? here's the code: section .text global _start _start: mov EAX, 8 mov EBX, filename mov ECX, 0700 int 0x80 mov EBX, EAX mov EAX, 4 mov ECX, text mov EDX, textlen int 0x80 mov EAX, 6 int 0x80 mov eax, 1 int 0x80 section .data filename db "./output.txt", 0 text db "hello world", 0 textlen equ $ - text thanks :)

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  • What is a good 64-bit NASM assembly reference?

    - by Xill
    I have been able to find plenty of 16 and 32-bit NASM assembly references like here, but the only thing I could find on 64-bit NASM was what was in the small section of the NASM manual here. Are there any good sites or books that would have a better explanation of 64-bit assembly (Windows or Linux/Unix) with some good code examples?

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  • Getting to grips with the stack in nasm

    - by MarkPearl
    Today I spent a good part of my day getting to grips with the stack and nasm. After looking at my notes on nasm I think this is one area for the course I am doing they could focus more on… So here are some snippets I have put together that have helped me understand a little bit about the stack… Simplest example of the stack You will probably see examples like the following in circulation… these demonstrate the simplest use of the stack… org 0x100 bits 16 jmp main main: push 42h push 43h push 44h mov ah,2h ;set to display characters pop dx    ;get the first value int 21h   ;and display it pop dx    ;get 2nd value int 21h   ;and display it pop dx    ;get 3rd value int 21h   ;and display it int 20h The output from above code would be… DCB Decoupling code using “call” and “ret” This is great, but it oversimplifies what I want to use the stack for… I do not know if this goes against the grain of assembly programmers or not, but I want to write loosely coupled assembly code – and I want to use the stack as a mechanism for passing values into my decoupled code. In nasm we have the call and return instructions, which provides a mechanism for decoupling code, for example the following could be done… org 0x100 bits 16 jmp main ;---------------------------------------- displayChar: mov ah,2h mov dx,41h int 21h ret ;---------------------------------------- main: call displayChar int 20h   This would output the following to the console A So, it would seem that call and ret allow us to jump to segments of our code and then return back to the calling position – a form of segmenting the code into what we would called in higher order languages “functions” or “methods”. The only issue is, in higher order languages there is a way to pass parameters into the functions and return results. Because of the primitive nature of the call and ret instructions, this does not seem to be obvious. We could of course use the registers to pass values into the subroutine and set values coming out, but the problem with this is we… Have a limited number of registers Are threading our code with tight coupling (it would be hard to migrate methods outside of their intended use in a particular program to another one) With that in mind, I turn to the stack to provide a loosely coupled way of calling subroutines… First attempt with the Stack Initially I thought this would be simple… we could use code that looks as follows to achieve what I want… org 0x100 bits 16 jmp main ;---------------------------------------- displayChar: mov ah,2h pop dx int 21h ret ;---------------------------------------- main: push 41h call displayChar int 20h   However running this application does not give the desired result, I want an ‘A’ to be returned, and I am getting something totally different (you will to). Reading up on the call and ret instructions a discovery is made… they are pushing and popping things onto and off the stack as well… When the call instruction is executed, the current value of IP (the address of the instruction to follow) is pushed onto the stack, when ret is called, the last value on the stack is popped off into the IP register. In effect what the above code is doing is as follows with the stack… push 41h push current value of ip pop current value of ip to dx pop 41h to ip This is not what I want, I need to access the 41h that I pushed onto the stack, but the call value (which is necessary) is putting something in my way. So, what to do? Remember we have other registers we can use as well as a thing called indirect addressing… So, after some reading around, I came up with the following approach using indirect addressing… org 0x100 bits 16 jmp main ;---------------------------------------- displayChar: mov bp,sp mov ah,2h mov dx,[bp+2] int 21h ret ;---------------------------------------- main: push 41h call displayChar int 20h In essence, what I have done here is used a trick with the stack pointer… it goes as follows… Push 41 onto the stack Make the call to the function, which will push the IP register onto the stack and then jump to the displayChar label Move the value in the stack point to the bp register (sp currently points at IP register) Move the at the location of bp minus 2 bytes to dx (this is now the value 41h) display it, execute the ret instruction, which pops the ip value off the stack and goes back to the calling point This approach is still very raw, some further reading around shows that I should be pushing the value of bp onto the stack before replacing it with sp, but it is the starting thread to getting loosely coupled subroutines. Let’s see if you get what the following output would be? org 0x100 bits 16 jmp main ;---------------------------------------- displayChar: mov bp,sp mov ah,2h mov dx,[bp+4] int 21h mov dx,[bp+2] int 21h ret ;---------------------------------------- main: push 41h push 42h call displayChar int 20h The output is… AB Where to from here? If by any luck some assembly programmer comes along and see this code and notices that I have made some fundamental flaw in my logic… I would like to know, so please leave a comment… appreciate any feedback!

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  • Assembleur Intel avec NASM en mode protégé, par Etienne Sauvage

    Bonjour, Vous trouverez à cette adresse : http://esauvage.developpez.com/tutor...tel-avec-nasm/ un parcours du combattant, un cheminement de quelqu'un qui, partant d'à peu près rien, essaye d'arriver à pas beaucoup plus mais quand même. Ce n'est pas vraiment un tutoriel parce que ça n'a pas d'objectif précis, ce n'est pas un cours car c'est riche en approximations. C'est plutôt le suivi d'un trappeur face à l'immensité canadienne. Néanmoins, comme j'ai remarqué que visiblement et contre toute attente, ça intéresse des gens, je crée cette discussion afin de recueillir les retours éventuels. Cordialement, Le chevalie...

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  • NASM: Count how many bits in a 32 Bit number are set to 1.

    - by citronas
    I have a 32 Bit number and want to count know how many bits are 1. I'm thinking of this pseudocode: mov eax, [number] while(eax != 0) { div eax, 2 if(edx == 1) { ecx++; } shr eax, 1 } Is there a more efficient way? I'm using NASM on a x86 processor. (I'm just beginning with assembler, so please do not tell me to use code from extern libraries, because I do not even know how to include them ;) ) (I just found http://stackoverflow.com/questions/109023/best-algorithm-to-count-the-number-of-set-bits-in-a-32-bit-integer which also contains my solution. There are other solutions posted, but unfortunatly I can't seem to figure out, how I would write them in assembler)

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  • Possiblity of loading/executing ELF files on OSX

    - by Daniel Brotherston
    I'm just curious as to the possibility of loading and executing elf files on OSX. I know the standard executable format is MACHO, but NASM is unable to generate debug information for MACHO objects (and I am required to use NASM). I imagine its a long shot, but I don't suppose I can use ELF files. I can build them with NASM, but I can't seem to even link them with LD.

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  • 80x86 16-bit asm: lea cx, [cx*8+cx] causes error on NASM (compiling .com file)

    - by larz
    Title says it all. The error NASM gives (dispite my working OS) is "invalid effective address". Now i've seen many examples of how to use LEA and i think i gots it right but yet my NASM dislikes it. I tried "lea cx, [cx+9]" and it worked; "lea cx, [bx+cx]" didn't. Now if i extended my registers to 32-bits (i.e. "lea ecx, [ecx*8+ecx]") everything would be well but i am restricted to use 16- and 8-bit registers only. Is here anyone so knoweledgeable who could explain me WHY my assembler doesn't let me use lea the way i supposed it should be used? Thanks.

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  • NASM shift operators

    - by Hudson Worden
    How would you go about doing a bit shift in NASM on a register? I read the manual and it only seems to mention these operators , <<. When I try to use them NASM complains about the shift operator working on scalar values. Can you explain what a scalar value is and give an example of how to use and <<. Also, I thought there were a shr or shl operators. If they do exist can you give an example of how to use them? Thank you for your time.

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  • NASM and a question about ADC - ASM 8086

    - by Tal
    Hello,I study assembly on High-school and I would like to try to make assembly programs at home. I downloaded NASM but I don't understand how to run the .s files with it - if you can write a simple way here to run it I'd glad :-) and in addition I have a question: when I use ADC for exmaple: AL = 01 and BL = 02, and CF = 1, when I make this: ADC AL,BL Will AL be 3 or 4? (with the CF addition or without?) Thank you!!

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