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• Assembly - Read next sector of a virtual disk

  - by ali

  As any programmer in the world at least once in his/her life, I am trying to create my "revolutionary", the new and only one operating system. :D Well, I am using a virtual emulator (Oracle VM Virtual Box), for which I create a new unknwon operating system, with a vmdk disk. I like vmdk because they are just plain files, so I can paste my boot-loader over the first 512 bytes of the virtual hard disk. Now, I am trying to read the next sector of this virtual disk, on which I would paste a simple kernel that would display a message. I have two questions: Am I reading the second segment (the first -512 bytes- is occupied by the bootloader) correctly? CODE: CitesteDisc: mov bx, 0x8000 ; segment mov es, bx mov bx, 0x0000 ; offset mov ah, 0x02 ; read function mov al, 0x01 ; sectors - this might be wrong, trying to read from hd mov ch, 0x00 ; cylinder mov cl, 0x02 ; sector mov dh, 0x00 ; head mov dl, 0x80 ; drive - trying to read from hd int 0x13 ; disk int mov si, ErrorMessage ; - This will display an error message jc ShowMessage jmp [es:bx] ; buffer Here, I get the error message, after checking CF. However, if I use INT 13, 1 to get last status message, AL is 0 - so no error is saved. Am I pasting my simple kernel in the correct place inside the vmdk? What I do is pasting it after the 512th byte of the file, the first 512 bytes, as I said, are the boot-loader. The file would look like this: BE 45 7C E8 16 00 EB FE B4 0E B7 00 B3 07 CD 10 <- First sector C3 AC 08 C0 74 05 E8 EF FF EB F6 C3 B4 00 B2 80 CD 13 BE 5D 7C 72 F5 BB 00 80 8E C3 BB 00 00 B4 02 B0 06 B5 00 B1 01 B6 00 B2 07 CD 13 BE 4E 7C 72 CF 26 FF 27 57 65 6C 63 6F 6D 65 21 00 52 65 61 64 69 6E 67 20 65 72 72 6F 72 21 00 52 65 73 65 74 74 69 6E 67 20 65 72 72 6F 72 21 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 AA <- Boot-loader signature B4 0E B0 2E CD 10 EB FE 00 00 00 00 00 00 00 00 <- Start of the second sector 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 So, this is the way I am trying to add the kernel to the second sector. What do you think is wrong with this? Thanks!

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• ARM assembly puzzle

  - by ivant

  First of all, I'm not sure if solution even exists. I spent more than a couple of hours trying to come up with one, so beware. The problem: r1 contains an arbitrary integer, flags are not set according to its value. Set r0 to 1 if r1 is 0x80000000, to 0 otherwise, using only two instructions. It's easy to do that in 3 instructions (there are many ways), however doing it in 2 seems very hard, and may very well be impossible.

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• assembly of pdp-11(simulator)

  - by lego69

  I have this code on pdp-11 tks = 177560 tkb = 177562 tps = 177564 tpb = 177566 lcs = 177546 . = torg + 2000 main: mov #main, sp mov #kb_int, @#60 mov #200, @#62 mov #101, @#tks mov #clock, @#100 mov #300, @#102 mov #100, @#lcs loop: mov @#tks,r2 aslb r2 bmi loop halt clock: tst bufferg beq clk_end mov #msg,-(sp) jsr pc, print_str tst (sp)+ clr bufferg bic #100,@#tks clr @#lcs clk_end:rti kb_int: mov r1,-(sp) jsr pc, read_char movb r1,@buff_ptr inc buff_ptr bis #1,@#tks cmpb r1,#'q bne next_if mov #0, @#tks next_if:cmpb r1,#32. bne end_kb_int clrb @buff_ptr mov #buffer,-(sp) jsr pc, print_str tst (sp)+ mov #buffer,buff_ptr end_kb_int: mov (sp)+,r1 rti ;############################# read_char: tstb @#tks bpl read_char movb @#tkb, r1 rts pc ;############################# print_char: tstb @#tps bpl print_char movb r1, @#tpb rts pc ;############################# print_str: mov r1,-(sp) mov r2,-(sp) mov 6(sp),r2 str_loop: movb (r2)+,r1 beq pr_str_end jsr pc, print_char br str_loop pr_str_end: mov (sp)+,r2 mov (sp)+,r1 rts pc . = torg + 3000 msg:.ascii<Something is wrong!> .byte 0 .even buff_ptr: .word buffer buffer: .blkw 3 bufferg: .word 0 Can somebody please explain how this part is working, thanks in advance movb r1,@buff_ptr inc buff_ptr bis #1,@#tks cmpb r1,#'q bne next_if mov #0, @#tks next_if:cmpb r1,#32. bne end_kb_int clrb @buff_ptr mov #buffer,-(sp) jsr pc, print_str tst (sp)+ mov #buffer,buff_ptr

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• Output character in assembly

  - by lolopolosko

  Please help me! How i can output character that moves around the perimeter of a rectangle (10*5 or 15*7) in console with TASM? .MODEL small .STACK 100h .CODE start: mov ah,03 int 10h mov cx,10 A: push cx mov ah,03 int 10h mov ah,02h inc dl int 10h mov al,42 int 29h pop cx LOOP A mov ah,4ch int 21h end start I do not know how to solve the problem...

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• Need some constructive criticism on my SSE/Assembly attempt

  - by Brett

  Hello, I'm working on converting a bit of code to SSE, and while I have the correct output it turns out to be slower than standard c++ code. The bit of code that I need to do this for is: float ox = p2x - (px * c - py * s)*m; float oy = p2y - (px * s - py * c)*m; What I've got for SSE code is: void assemblycalc(vector4 &p, vector4 &sc, float &m, vector4 &xy) { vector4 r; __m128 scale = _mm_set1_ps(m); __asm { mov eax, p //Load into CPU reg mov ebx, sc movups xmm0, [eax] //move vectors to SSE regs movups xmm1, [ebx] mulps xmm0, xmm1 //Multiply the Elements movaps xmm2, xmm0 //make a copy of the array shufps xmm2, xmm0, 0x1B //shuffle the array subps xmm0, xmm2 //subtract the elements mulps xmm0, scale //multiply the vector by the scale mov ecx, xy //load the variable into cpu reg movups xmm3, [ecx] //move the vector to the SSE regs subps xmm3, xmm0 //subtract xmm3 - xmm0 movups [r], xmm3 //Save the retun vector, and use elements 0 and 3 } } Since its very difficult to read the code, I'll explain what I did: loaded vector4 , xmm0 _ p = [px , py , px , py ] mult. by vector4, xmm1 _ cs = [c , c , s , s ] _____________mult---------------------------- result,______ xmm0 = [px*c, py*c, px*s, py*s] reuse result, xmm0 = [px*c, py*c, px*s, py*s] shuffle result, xmm2 = [py*s, px*s, py*c, px*c] ___________subtract---------------------------- result, xmm0 = [px*c-py*s, py*c-px*s, px*s-py*c, py*s-px*c] reuse result, xmm0 = [px*c-py*s, py*c-px*s, px*s-py*c, py*s-px*c] load m vector4, scale = [m, m, m, m] ______________mult---------------------------- result, xmm0 = [(px*c-py*s)*m, (py*c-px*s)*m, (px*s-py*c)*m, (py*s-px*c)*m] load xy vector4, xmm3 = [p2x, p2x, p2y, p2y] reuse, xmm0 = [(px*c-py*s)*m, (py*c-px*s)*m, (px*s-py*c)*m, (py*s-px*c)*m] ___________subtract---------------------------- result, xmm3 = [p2x-(px*c-py*s)*m, p2x-(py*c-px*s)*m, p2y-(px*s-py*c)*m, p2y-(py*s-px*c)*m] then ox = xmm3[0] and oy = xmm3[3], so I essentially don't use xmm3[1] or xmm3[4] I apologize for the difficulty reading this, but I'm hoping someone might be able to provide some guidance for me, as the standard c++ code runs in 0.001444ms and the SSE code runs in 0.00198ms. Let me know if there is anything I can do to further explain/clean this up a bit. The reason I'm trying to use SSE is because I run this calculation millions of times, and it is a part of what is slowing down my current code. Thanks in advance for any help! Brett

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• Finding which contigs go into any given scaffold in an 454-Newbler assembly

  - by Martin Malmstrøm

  I guess there should be a quite simple script for calling which contigs go into which scaffolds. This is 454 data assembled with Newbler. Thanks!

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• What am I doing wrong? (Simple Assembly Loop)

  - by sunnyohno

  It won't let me post the picture. Btw, Someone from Reddit.programming sent me over here. So thanks! TITLE MASM Template ; Description ; ; Revision date: INCLUDE Irvine32.inc .data myArray BYTE 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 .code main PROC call Clrscr mov esi, OFFSET myArray mov ecx, LENGTHOF myArray mov eax, 0 L1: add eax, [esi] inc esi loop L1 call WriteInt exit main ENDP END main Results in: -334881242

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• Do an assembly have multiple namespaces or is composed of single namespace

  - by Shantanu Gupta

  Can an assemble have multiple namespaces or is composed of single namespace.

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• What does ESP mean in assembly?

  - by Mask

  ESP = ? stack pointer What does E stand for here?

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• Call/Ret in x86 assembly embedded in C++

  - by SP658

  This is probably trivial, but for some reason I can't it to work. Its supposed to be a simple function that changes the last byte of a dword to 'AA' (10101010), but nothing happens when I call the function. It just returns my original dword __declspec(naked) long function(unsigned long inputDWord, unsigned long *outputDWord) { _asm{ mov ebx, dword ptr[esp+4] push ebx call SET_AA pop ebx mov eax, dword ptr[esp+8] mov dword ptr[eax], ebx } } __declspec(naked) unsigned long SET_AA( unsigned long inputDWord ) { __asm{ mov eax, [esp+4] mov al, 0xAA ret } }

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• Help with optimizing C# function via C and/or Assembly

  - by MusiGenesis

  I have this C# method which I'm trying to optimize: // assume arrays are same dimensions private void DoSomething(int[] bigArray1, int[] bigArray2) { int data1; byte A1; byte B1; byte C1; byte D1; int data2; byte A2; byte B2; byte C2; byte D2; for (int i = 0; i < bigArray1.Length; i++) { data1 = bigArray1[i]; data2 = bigArray2[i]; A1 = (byte)(data1 >> 0); B1 = (byte)(data1 >> 8); C1 = (byte)(data1 >> 16); D1 = (byte)(data1 >> 24); A2 = (byte)(data2 >> 0); B2 = (byte)(data2 >> 8); C2 = (byte)(data2 >> 16); D2 = (byte)(data2 >> 24); A1 = A1 > A2 ? A1 : A2; B1 = B1 > B2 ? B1 : B2; C1 = C1 > C2 ? C1 : C2; D1 = D1 > D2 ? D1 : D2; bigArray1[i] = (A1 << 0) | (B1 << 8) | (C1 << 16) | (D1 << 24); } } The function basically compares two int arrays. For each pair of matching elements, the method compares each individual byte value and takes the larger of the two. The element in the first array is then assigned a new int value constructed from the 4 largest byte values (irrespective of source). I think I have optimized this method as much as possible in C# (probably I haven't, of course - suggestions on that score are welcome as well). My question is, is it worth it for me to move this method to an unmanaged C DLL? Would the resulting method execute faster (and how much faster), taking into account the overhead of marshalling my managed int arrays so they can be passed to the method? If doing this would get me, say, a 10% speed improvement, then it would not be worth my time for sure. If it was 2 or 3 times faster, then I would probably have to do it. Note: please, no "premature optimization" comments, thanks in advance. This is simply "optimization".

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• Scan for first zero bit (Assembly)?

  - by cthulhu

  I have some numbers in AH, AL, BL, BH registers. I need to check whether there is 0 bit in each of the registers in left half of the number. If yes, then put into check variable value 10 else -10. How can I do this? I tried something like that: org 100h check dw 0 mov ah, 11111111b mov al, 11111111b mov bl, 11111111b mov bh, 11111111b mov check, -10 shr ah, 4 shr al, 4 shr bl, 4 shr bh, 4 cmp ah, 0Fh jz first first: cmp al, 0Fh jz second second: cmp bl, 0Fh jz third third: cmp bh, 0Fh jz final final: mov check, 10 ret

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• assembly: data segment when called from c or created as an independet programm

  - by aristotaly

  im confuse about this i dont think that there shuld be any difference in both casess the programm ends up as exe file please help if you think a differ....

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• C#: Custom assembly directory

  - by Svish

  Say we have an application which consists of one executable and 5 libraries. Regularly all of these will be contained in one directory and the libraries will be loaded from there. Is it possible to do so that I can have for example some of the libraries in one directory called Lib, and the rest in one called Lib2? So that the application directory would only contain the executable itself and the other assemblies would be contained in various logical directories. How can I do this? And I would like to know how to do the loading of the assemblies, but also how to make the building of the application put the assemblies in the right directory.

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• Question about inserting assembly code in C++

  - by Bruce

  I am working on VC++ compiler. I want to accomplish the following The variables s.AddrFrame.Offset and s.AddrStack.Offset contain the value of EBP and ESP respectively. I want to extract the value of old EBP and the return address. Assuming the address EBP + 1 contains the old 32 bit EBP value and EBP + 5 the return address I wrote the following code: unsigned int old_ebp = 0; unsigned int ret_addr = 0; __asm{ mov old_ebp, DWORD PTR [s.AddrFrame.Offset + 1] mov ret_addr, DWORD PTR [s.AddrStack.Offset + 5] } But this is not compiling xxxx.cpp(1130) : error C2415: improper operand type Please Help

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• Assembly instruction address...

  - by Narek

  Why avery time when I disassembly the same .exe file the same instruction is in the same address? And what address is that(RAM? HDD? Virtual?)?

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• About using assembly with c

  - by kristus

  Hi. I've sort of just finished a mandatory task at school, and I'm about to deliver it. But then I came across something that was unfamiliar, header files. :( What I've got: test-program.c task_header.h function1.s function2.s function3.s function4.s test-program.c: #include <stdio.h> #include <stdlib.h> #include <string.h> #include "task_header.h" . .. ... task_header.h: extern void function1(...); extern void function2(...); extern int function3(...); extern void function4(...); And then I use the command: gcc -m32 -o runtest test-program.c function1.s function2.s function3.s function4.s Is this a proper way to do it, or is it possible to modify it? So I can type: gcc -m32 -o runtest test-program.c ?

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• Help translating from assembly to C

  - by user324994

  I have some code from a function subl $24, %esp movl 8(%ebp), %eax cmpl 12(%ebp), %eax Before the code is just the 'ENTER' command and afterwards there's an if statement to return 1 if ebp eax or 0 if it's less. I'm assuming cmpl means compare, but I can't tell what the concrete values are. Can anyone tell me what's happening?

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• Running ARM assembly code in Android

  - by Robert Joseph Dacunto

  I've been following the guide posted here, trying to get this Hello, World program to run on my Samsung Galaxy S3. It's rooted already, and I successfully pushed the "hello" file onto the sdcard. Now when I enter the shell as the superuser (# instead of $), and try to run the file, I get "cannot execute - permission denied". I used chmod 755 hello to see if that would fix it, still nothing. Is there something I'm missing? This is my first time fiddling around with Android, just got the phone, and wanted to see if I could get this to work. Very new to it all. Thanks!

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• x86 Assembly - printf doesn't print without "\n"

  - by Bitani

  So I'm confused. I'm going through the book "Programming from the Ground Up" and am working with using libraries. printf is working just fine so long as I include a "\n" in the string, but without it it will print absolutely nothing. Any idea why this happens? Code: .section .data my_str: .ascii "Jimmy Joe is %d years old!\n\0" my_num: .long 76 .section .text .globl _start _start: pushl my_num pushl $my_str call printf movl $1, %eax movl $0, %ebx int $0x80 Also, when I use -m elf_i386 for 32-bit mode and -dynamic-linker /lib/ld-linux.so.2 -lc to link, I get the warning ld: skipping incompatible /usr/lib64/libc.so when searching for -lc If that makes any difference, or if anybody has any suggestions as to how to have it load the 32-bit library directly. Thanks!

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• Sparc Assembly Call currupts data

  - by Sigge

  I am at the moment working with some assembler code for the Sparc processor family, and i am having some truble with a piece of code.. I think the code and output explains more, but in the short.. When i do a call to the function println my varaibels that i have written to the %fp - 8 memory location is destoryed.. here is my assembler code that i am trying to run !PROCEDURE main .section ".text" .global main .align 4 main: save %sp, -96, %sp L1: set 96, %l0 mov %l0, %o0 call initObject ; nop mov %o0, %l0 mov %l0, %o0 call Test$go ; nop mov %o0, %l0 mov %l0, %o0 call println ; nop L0: ret restore !END main !PROCEDURE Test$go .section ".text" .global Test$go .align 4 Test$go: save %sp, -96, %sp L3: mov %i0, %l0 set 0, %l0 set -8, %l1 add %fp,%l1, %l1 st %l0, [%l1] set 1, %l0 mov %l0, %o0 call println ; nop set -8, %l0 add %fp,%l0, %l0 ld [%l0], %l0 mov %l0, %o0 call println ; nop set 1, %l0 mov %l0, %i0 L2: ret restore !END Test$go Here is the assembler code for the println code .global println .type println,#function println: save %sp,-96,%sp ! block 1 .L193: ! File runtime.c: ! 42 } ! 43 ! 45 /** ! 46 Prints an integer to the standard output stream. ! 47 ! 48 @param i The integer to be printed. ! 49 */ ! 50 void println(int i) { ! 51 printf("%d\n", i); sethi %hi(.L195),%o0 or %o0,%lo(.L195),%o0 call printf mov %i0,%o1 jmp %i7+8 restore This is the out put i get when i run this piece of assembler code 1 67584 1 As u can see, the data that is located at %fp - 8 has been destroyed.. please all feedback is apritiated

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• Sparc Assembly Call corrupts data

  - by Sigge

  I am at the moment working with some assembler code for the Sparc processor family, and i am having some truble with a piece of code.. I think the code and output explains more, but in the short.. When i do a call to the function println my varaibels that i have written to the %fp - 8 memory location is destoryed.. here is my assembler code that i am trying to run !PROCEDURE main .section ".text" .global main .align 4 main: save %sp, -96, %sp L1: set 96, %l0 mov %l0, %o0 call initObject ; nop mov %o0, %l0 mov %l0, %o0 call Test$go ; nop mov %o0, %l0 mov %l0, %o0 call println ; nop L0: ret restore !END main !PROCEDURE Test$go .section ".text" .global Test$go .align 4 Test$go: save %sp, -96, %sp L3: mov %i0, %l0 set 0, %l0 set -8, %l1 add %fp,%l1, %l1 st %l0, [%l1] set 1, %l0 mov %l0, %o0 call println ; nop set -8, %l0 add %fp,%l0, %l0 ld [%l0], %l0 mov %l0, %o0 call println ; nop set 1, %l0 mov %l0, %i0 L2: ret restore !END Test$go Here is the assembler code for the println code .global println .type println,#function println: save %sp,-96,%sp ! block 1 .L193: ! File runtime.c: ! 42 } ! 43 ! 45 /** ! 46 Prints an integer to the standard output stream. ! 47 ! 48 @param i The integer to be printed. ! 49 */ ! 50 void println(int i) { ! 51 printf("%d\n", i); sethi %hi(.L195),%o0 or %o0,%lo(.L195),%o0 call printf mov %i0,%o1 jmp %i7+8 restore This is the out put i get when i run this piece of assembler code 1 67584 1 As u can see, the data that is located at %fp - 8 has been destroyed.. please all feedback is apritiated

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• Referenced assembly won't load in new thread on IIS 7

  - by DanielC

  I have a process in which a user uploads a file to a web site where the file is then processed and uploaded into the database. The process of validating the file could take several minutes so as soon as the file is uploaded I create a new thread and I do my processing on this second thread. This works great on my local machine but doesn't work at all on my IIS 7 test server. After some investigating I found the problem is that the process is trying to load a reference to Castle and it can't find the DLL. I have a copy of Castle DLLs in my bin and it works elsewhere in my app. I ran Fuslog and discovered that it is trying to load castle from the wrong location. It is trying to load from c:/windows/system32/inetsrv/. It appears that under IIS 7 the second thread is executing in a different context or something. So the question is what can I do to get it to find Castle in the application BIN folder?

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• Good assembly tutorial for windows with eiter fasm or nasm

  - by The new guy

  I have spent the last 3 hours google and bing for a good asm tutorial(x86 variety). I have been on this site for many of these results. Non have really been sufficient. Mainly because while i like learning theory, i learn it best via practice, while for example pc-asm has about 20-30 pages of theroy before anything practical. I was wondering if there was a tutorial or online pdf (or cheap book(<£20)) that i could use that suits my style of learning. Please state if this is not possibke Thank you for your time

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• MOV Assembly Instruction

  - by anonymous

  What does this instruction do? mov (%r11,%r12,1),%edx Thanks.

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