Write a simple assembly code where you count from from eax to ebx. Writing to memory is a "store" (mov [a], eax).

Write a simple assembly code where you count from from eax to ebx I than compare eax to ebx and increment eax and jump if not zero. inc . At the end of your code ecx =0×00001900. But starting out can be a daunting task. Finally, this: mov [eax], ebx stores the value in ebx into the memory location pointed to Write assembly language code using what you know so far (do not look ahead in the book just yet) to determine the length of 'numbers'. 11,00,01,10 in ebx and eax register. But, to be clear you could send the extended value to another register, such as movzx EAX, BX — don't have to sign/zero extend into the same Nov 9, 2013 · %include "asm_io. So by moving the value 0x1 to EAX register and calling the INT 0x80 in your program, you can make the process go execute the code in Kernel which will stop (exit) the current running process (on Linux, x86 Intel CPU). – Nov 7, 2018 · So, I've been trying to learn some assembly and I saw an example of an addition but I don't really understand one thing: section . code main PROC mov ESI, OFFSET array1 ;ESI now points to the first item of array1 mov EDI, SIZEOF array1 add EDI, OFFSET array1 sub EDI, TYPE array1 ;EDI now points to the last mov eax, [ebx]; Move the 4 bytes in memory at the address contained in EBX into EAX: mov [var], ebx; Move the contents of EBX into the 4 bytes at memory address var. When you next do this: MOVL EBX, (%EAX) MOVL EAX, (%EBX) Nov 13, 2020 · You need the system call number in eax and the arguments in ebx, ecx, edx, esi, edi, ebp in that order. (Note, var is a 32-bit constant). First solution is to keep counting in ecx and compare it with array length. o ld: warning: cannot find entry symbol _start; defaulting to 0000000008048080 root@bt:~/Arena# ld -o out a. Your code needs to preserve the values of other registers, including ebx and edi, or you might get a bug when you return. h" int f() { __asm { mov eax, 42 // setting EAX to 42 here } } int main() { int i = f(); printf("%i\n", i); return 0; } and eax, 1 mov ebx, eax In assembly code, because you have few registers, their contents tend to be precious, so destroying one register's content in computing a new result is generally avoided. Like what is the need for all these instructions. bss . notlowercase: inc eax jmp . – Oct 4, 2014 · Hopefully what I'm asking makes sense. regs. Write a simple assembly language program in AT&T syntax. And if I input 11 or 00 I want to quit from the procedure. eax = 4: System call number for sys_write. text global _start _start: mov eax, '3' sub eax, '0' mov ebx, '4' sub ebx, '0' add eax, ebx add eax, '0' mov [sum], eax mov ecx, msg mov edx, len mov ebx, 1 mov eax, 4 int 0x80 mov ecx, sum mov edx, 1 mov ebx, 1 mov eax, 4 int 0x80 mov eax, 1 int 0x80 section . A 16-bit Code Segment register or CS register stores the starting address of the code segment. Even when I write more complicated functions, in the end it is always ecx just before the WriteLine() function. This address arithmetic can be used itself through lea instruction, when the CPU will do the address math, but instead of loading value from memory it will just store the calculated address, so: Mar 13, 2011 · %ebx is the status code for the exit system call This means that whatever is stored in %ebx will be returned to the Operating System. Many memory accesses on modern processors will be more efficient if they follow the alignment rules (such as a 4-byte value having to be aligned to a 4-byte boundary). Upload Image. Data Segment − It contains data, constants and work areas. In AT&T assembly and in simple assembly. Write a procedure named “CheckPrime” that sets the EBX register to 1 if the 32-bit integer passed in the EAX register is prime. Add comments also. I want to see the value in ebx register there for I mov it to eax and then return. Mar 13, 2016 · The corrected description for fragment A is: mov eax, 5 ; move 5 into register eax add eax, ebx ; add contents of ebx to eax, changing eax nop ; no operation nop ; no operation push ebx ; push contents of ebx onto the stack nop ; no operation pop ebx ; pop top of the stack into ebx call [eax] ; call the subroutine pointed to at location [eax] Sep 22, 2020 · @notevention: You're still using EBX as an argument to those int 0x80 Linux system calls, you're just relying on Linux's behaviour of initializing it (and other registers except ESP) to 0 in a static executable. text ;code segment global _start ;must be declared for linker _start: ;tell linker entry point mov edx,len ;message length mov ecx,msg ;message to write mov ebx,1 ;file descriptor (stdout) mov eax,4 ;system call number (sys_write) int 0x80 ;call kernel mov eax,1 ;system call number (sys_exit) int 0x80 ;call kernel segment . – Apr 24, 2016 · Your code is completely wrong. You don't need to include the variable declarations, a function or anything like that, just show the 1 to 4 lines of code in C that express what the above assembly Sep 2, 2015 · I am not really good in assembly so there might exist a better answer (this one works). If you don't care what will be left in EBX after the operation, you can also use XCHG EAX,EBX (which often has a shorter encoding on x86). data count BYTE -1 val1 SDWO Sep 28, 2011 · mov EAX, dword ptr [ESI + ECX * 4] ^ ^ | +-- source in a readable syntax +----- destination Which has the form: mnemonic destination, source (exactly the other way round). The function's purpose is to add two integer arguments. This code works with YASM. Include a "register use" list in your code. 3. TITLE Reversing an array without using oneother array INCLUDE Irvine32. At the end of your code ecx = 0x00001900. To get the result of (1234h - 123h) into the register EAX you should code: MOV EAX, val_A MOV EBX, val_B SUB EAX, EBX Just to be clear again, SUB instruction does work like MOV and that why the result moves into the first register Jul 31, 2013 · You would also go a long way toward making your code readable by using equ values rather than magic numbers and adding comments: fn_exit equ 0 fb_read equ 3 fn_write equ 4 : mov eax, fn_write ; write mov ebx, 1 ; to stdout (fd 1) mov ecx, name ; text to write mov edx, name_L ; length of text to write Question: After running the Assembly language code below, what are the correct values of EAX, EBX, ECX? mov eax, 11119999h mov ebx, 12340909h mov ecx, 22223333h push eax push ebx push ecx pop bx pop ax pop cx pop cx pop bx pop ax EAX= 12341111 EBX= 12342222 ECX= 2222 1234 EAX= 11111234 EBX= 12349999 ECX= 99991234 EAX= 111111111 EBX= 12342222 ECX= 1234 2222 EAX= Oct 16, 2021 · MOV EAX, EBX actually doesn't move data from one place to another, it does copy, because EBX keeps its original contents. notdigit inc ecx jmp . Apr 2, 2013 · This is a hw problem. text global _start _start: jmp short GoToFileName open: pop esi ; address of file name mov edx, 0x1ff ; 0777 mov ecx, 0x41 ; O_CREAT | O_WRONLY mov ebx, esi ; ebx gets address of file name mov eax, 0x5 ; SYS_open int 0x80 mov ebx, eax ; write resulting file descriptor in EBX jmp short TextInput write: pop esi ; address of input string Oct 15, 2013 · You want. code main proc mov esi,OFFSET array mov ecx,LENGTHOF array mov ebx,0 ; Start sum at 0 cld ; Clear the direction bit (look up the LODS instruction!) lodsd ; Get the first value to start mov edx, eax ; Save "previous" element read in edx dec ecx ; Decrement Sep 12, 2019 · If you want to write the result to a third operand instead of overwriting one of the source operands, the standard solution is to first move one of the operands to the target and then use the target with a two operand instruction. text global _start ;must be declared for using gcc _start: ;tell linker entry Apr 19, 2016 · A common function calling convention for x86 is cdecl, where a function's integral return value is saved in the EAX register. A register like %eax on the other hand contains a 32-bit integer. This question hasn't been solved yet! Sep 29, 2018 · The 2nd half of my answer on What parts of this HelloWorld assembly code are essential if I were to write the program in assembly? has the same i386 Linux code in NASM, with only different variable names. Aug 30, 2020 · In programming in general, but assembly in particular, just because something works once under special conditions doesn't mean the code is correct. There are three main segments −. data format db "Number %ld", 0x0a, 0 ; Format string for printf result dq 0 ; Quad word to store the EDX:EAX result in segment . Sep 22, 2024 · Assembly Language Code Samples Basic Algebraic Functions Let us see a Syscall number for write mov ebx, 1 ; File mov ecx, count ; Load the count value into ECX mov ebx, 1 Mar 28, 2021 · mov val1,eax and not mov val1,al. A dd directive doesn't "store" in that sense, though. Don't use Sub instruction and you must use hex numbers only as immediate numbers. Now you can write your Assembly code in this file. What mul ebx does is ebx*eax and stores the result in edx:eax (the higher order bits go in edx when eax is not big enough to hold the result, in your example this is not a problem though). file descriptor (1 for standard output) in ebx. In a pseudo-C notation, this would be: eax = *ebx. I am also still not sure what mov [eax+1], ecx does? Take the value of EAX then add 1; now this value (eax + 1) is a pointer at which you'll store the 32-bit (assuming no size override) value in ECX. end cmp dl, '0' jb . mov eax, STRING_VARIABLE xor ebx, ebx xor ecx, ecx . data buff_size: . code main proc mov eax, num1 mul num2 push ebx push edi mov edi, OFFSET Buffer ; Begin of the buffer mov ebx, 10 ; CONST push ebx ; Sentinel . mov eax, [esi-4]; Move 4 bytes at memory address ESI + (-4) into EAX: mov [esi+eax], cl; Move the contents of CL into the byte at address ESI+EAX VIDEO ANSWER: The number of the row that has the largest length is returned to if remeid calls the largest road as 2 to the array of ants. Writing to memory is a "store" (mov [a], eax). Even if it did, the convention only says what you must preserve, not how. Using Irvine32 library you can print the contents of EAX as a signed integer by calling the Jul 27, 2013 · section . This gets you a library routine you can call from other programs. Every time I input 01 or 10 I need to jump at l1. on the stack) and restore them to Segments are specific areas defined in a program for containing data, code and stack. Also for your own code you do not have to follow the convention anyway. 386 . Math Mode May 2, 2012 · Yes this is legal gcc syntax, but buggy unless you put that inside a function with __attribute__((naked)) which contains only inline asm. text main: push ebx mov ax, 0x1234 mov bx, 0x10 mul bx and eax, 0x0000ffff ; clear upper bits of eax shl edx, 16 ; shift DX into position or eax, edx ; and combine push eax push format call printf add esp, 8 mov eax, 0 pop ebx ret section . Hi i have a question about assembly x86 this is my code INCLUDE Irvine32. EBX: "Extended Base" - often used as a pointer to data in the data segment of memory. That's also why you pad paths with redundant // to make them a multiple of 4 bytes. Your saved registers are not different from any local variables, you can even access them with mov instructions instead of push/pop if you like and you may put them under your other variables if you don't want to use bigger offsets. Feb 9, 2016 · Here is an example how to print the 64 bit number with printf. It has a fairly complete explanation of what's going on when making a system call. text global main extern printf main: ; Store the 64 bit number in the quad word "result" mov edx, 0x21C3677C ; Store the EDX value mov eax, 0x82B40000 ; Store the EAX Please try the following code: Refer to the description of mnemonics for understand perfectly. It depends on the context in which you name a register whether the value of that register is relevant at all. Nov 17, 2021 · In your code you jump to the label adding: when the number is even, but when it is odd you fall through in that same label, so you always do the sum. edi); pretty much the same thing no change what so ever. Write assembly language code using what you know so far (do not look ahead in the book just yet) to determine the length of 'numbers'. text global _start ;must be declared for using gcc _start: ;tell linker entry point ; allocate 24B temporary buffer for ASCII number sub esp,24 ; output test numbers in loop mov esi,testnumbers testNumbersLoop: mov eax,[esi] mov edx,[esi+4] mov edi,esp ; call the routine call integer64btoascii ; add new line to output mov [edi],byte 10 Mar 6, 2015 · Section . text global _start _start: mov eax, 0x14 ; GET_PID call int 0x80 ; Call mov ebx, 0xA ; Set divider to 10 mov ebp, PID+6 ; Save the May 20, 2011 · Because with the ret command, the value in eax is returned to the caller function. I am running a gdb debugger on some assembly code. x86-64 repurposed the 0x40. I just want to ask that is there any rule on the sequence of using %eax, %edx, %ecx register when you use them with in the same function frame. data array1 DWORD 10d,20d,30d,40d,50d,60d,70d,80d,90d . Write an assembly code that does the following: eax =(ecx+ edx)−(eax+ebx) 2. Running Assembly code in Linux. notlowercase . You then dereference the memory, moving the actual values into the registers of the same name: MOVL (%EAX), EAX MOVL (%EBX), EBX EAX and EBX no longer contain memory addresses; they now contain the contents from those addresses. In a pseudo-C notation, this would be: eax = ebx. Engineering; Computer Science; Computer Science questions and answers; Write an assembly code that asks two digits from the user, store the digits in the EAX and EBX register, respectively, add the values, store the result in a memory location 'res' and finally display the result. Code Segment − It contains all the instructions to be executed. If the 32-bit integer passed in the EAX register is not prime, then the procedure should set EBX to 0. For example, In c++ the code is like this-while (eax != ebx) {eax++} For example, you put 4 in eax and 8 in ebx, and then you have to write a loop that adds on to eax but stops when eax and ebx are both 8. – Sep 7, 2010 · The and $0xfffffff0,%esp instruction is a way to force esp to be on a specific boundary. … Nov 30, 2009 · As you can see the table points the CPU to execute a system call. 64bit_mode: lea rdx, [rel _start] ; An instruction that won't assemble in 32-bit mode. This is used to ensure proper alignment of variables. Assume that you are given values in eax, ebx, ecx. Feb 2, 2019 · You can't do mov [eax], [ebx] because that implies a machine instruction that will let you specify two memory operands. What do the numbers represent? I tried calling x 134522400 and x/s 134522400, but both just returned to me "\372\001". loop . Comment Oh and what you call instructions, are really parameters. 64bit_mode ; REX jcc still works ;jmp . cmp [sign], ebx is comparing 4 bytes not 1. segment . globl _start # telling where program execution should start _start: popl %eax # Get the number of arguments popl %ebx # Get the program name popl %ebx # Get the first actual argument - file to read # open the file movl $5, %eax # open Sep 27, 2016 · This works, though I am using Irvine32. Write an assembly code. Lets compare for example if greater or equal: main: comp eax, ebx jge greater_or_equal greater_or_equal: ; your code if greater or equal Oct 5, 2014 · I want to add two-digit numbers in NASM(Linux). data num1 dword 1000000 num2 dword 1000000 Buffer byte 32 dup(0) . loop: mov dl, [eax] cmp dl, 0 jz . mov %ebx, %ecx imul %eax, %ecx Apr 8, 2017 · The brackets mean a level of indirection. end: ; ebx contains the lowercase letter count ; ecx The instruction adc eax, ebx adds register eax, register ebx, and the contents of the carry flag, and then store the result back to eax. Jul 20, 2016 · On the x86-64/x64 ABI, or the __msfastcall convention on 32-bit x86, the first two arguments would be passed in ecx and edx, and the return value would be in eax. data hello db 'Hello World', 0 section . The correct code is: mov ebx, 0; mov esi, [arr]; mov ecx, [arr_size]; jecxz emptyarr sumeven: push ebx; mov eax, [ESI]; mov ebx, 2; cdq idiv ebx; cmp edx, 0; pop ebx; jne notadding; add ebx, dword Apr 17, 2019 · I want to input . mov ax,1234h means immediate, put 1234h in AX mov [1234h],ax has a level of indirection in the same way as [bx] above, the thing in My code is supposed to print an 'A' on the top left corner of the display. . Similarly, in megabyte : megabyte: mov eax, [input2] cdq mov ebx, 1048576 idiv ebx mov [input2], eax As in the previous code, now, input2 contains the result you want. What I have so far is: INCLUDE Irvine32. bss sock_fd resd 1 ; socket fd = 32- bits connect_fd resd 1 buffer resb buflen ; reserve 1000 bytes for 'buffer' A few questions on your previous server/bind code: You use: Oct 24, 2023 · section . There are 2 steps to solve this one. Write an assembly code that does the following: eax = (ecx + edx ) - (eax + ebx) 2. To add two simple numbers, I use the following code: section . Is this the value? I guess because it's 45, what equal to it, and let's try to make up, so it's 10 to 453. seems to be the same as the two above. Example: Assume that Initially eax = 0x15DBCB19. Being able to read and write code in low-level assembly language is a powerful skill to have. lcomm buff, 18 . SECTION . It enables you to write faster code, use machine features unavailable in C, and reverse-engineer compiled code. Oct 31, 2024 · We use the mov instruction to load registers with specific values for a sys_write system call. Here is a version of James Parker's code converted to run on x86/x86_64 Linux. If you modify registers, you must use GNU C Extended Asm constraints / clobbers to tell the compiler about it; stepping on the compiler's registers can cause really weird results. write takes three arguments so you need: system call number (4) in eax. Then see what the assembler output looks like (with optimizations enabled), to see if there's any reason what so ever to use inline asm Jul 3, 2022 · This is my code so far. Write one line of code in assembly May 28, 2015 · EAX and EBX start out containing memory locations. except it attempts to append as much fully set bits in front of the value moved as possible. ECX: The count register, typically used for loop counters. Now let’s dive into more advanced concepts! Procedures, Subroutines and Macros help structure code Oct 10, 2014 · Linux Version. Write an assembly code that does the following:eax = (ecx + edx ) -(eax +ebx) 2. I missed something? 1. TITLE SOF_Sum INCLUDE Irvine32. So I wrote this code: mov eax, operanda mov ebx, operandb add eax, ebx But than I understood that my operand is big than 32-bit. section . You have to use increment/decrement instructions. Now MOVSX i'm having trouble converting to a simple C code. I have written some code below but probably not correct. _start: ;tell linker entry point mov edx, len ;message length mov ecx, msg ;message to write mov ebx, 1 ;file descriptor (stdout) mov eax, 4 ;system call number (sys_write) int 0x80 ;call kernel mov eax, 1 ;system call number (sys_exit) int 0x80 ;call kernel Input: You provide the necessary details, including what you want the code to do and specific programming needs. bss sock_fd resd 1 ; socket fd = 32- bits connect_fd resd 1 buffer resb buflen ; reserve 1000 bytes for 'buffer' A few questions on your previous server/bind code: You use: Nov 24, 2011 · I tried to write a program in Assembly that calculate operand_a + operand_b. bss PID: resb 8 ; Reserve space for result SECTION . Then, after declareing mask as int, the function loop will fall into an infinite loop when result won't become positive via result ^= n;. Question: After running the Assembly language code below, what are the correct values of EAX, EBX, ECX? mov eax, 11119999hmov ebx, 12340909hmov ecx, 22223333hpush ebxpush eaxpush ecxpop axpop bxpop cxpop axpop cxpop bxQuestion 12 options: EAX=11111234 EBX=12341234  ECX=09092222 EAX=11111111 EBX=12341234  ECX=22220909 EAX=11111111 EBX=12340909 May 4, 2017 · mov eax, ebx simply copies the value in ebx into eax. Registers can be used in your software directly with instructions such as mov, add or cmp. d. Jul 16, 2020 · Here's that code with explanatory comments: mov edx, len ; length of string to print mov ecx, msg ; address of string to print mov ebx, 1 ; file descriptor: 1 = stdout mov eax, 4 ; syscall #4 is sys_write int 0x80 ; execute the syscall Syscall #1: sys_exit Write a simple assembly code where you count from from eax to ebx. The instruction is the whole statement. Nov 6, 2024 · In the last part, we understood how to code basic arithmetic, loops and conditions in Assembly. The data is already there when your program starts. Feb 1, 2014 · In the asm code it creates, I find one sentence as below: mov eax, ds:(__dso_handle_ptr - 804DFF4h)[ebx] I have never seen asm code like this, and use nasm/masm to directly assembly it would generate errors After searching the code, I found this: __dso_handle dd 0 But I don't found __dso_handle_ptr which is very strange Dec 4, 2021 · Also, I check what is in eax and it 1 too(by printf). text global _start _start: ; write the string to stdout mov eax, 4 ; syscall number for sys_write mov ebx, 1 ; file descriptor 1 is stdout mov ecx, hello ; pointer to the string mov edx, 12 ; length of the string int 0x80 ; call kernel ; exit the program mov eax, 1 Jul 3, 2013 · The write system call takes a buffer of characters to print, pointed at by %ecx with a length given by %edx. If you use these registers for your own purposes, you have to first save their values somewhere (e. text # declaring our . Write one line of code in assembly to Oct 24, 2023 · section . Writing efficient assembly code is an art form—it's about understanding the hardware, optimizing every instruction, and squeezing out every last b Sep 14, 2019 · mov eax, 47 push eax mov eax, 11 push eax pop ebx Which value is located in ebx? I'm not really sure what should be in ebx, probably a random value? On the stack, there should be (from high to low) 47, 11 but we know nothing about ebx. mov bx,ax means put ax in bx or register direct, use the register directly to store the value mov [bx],ax means register indirect, take the value in the register and use that as an address of the place to store the value. Note this is linux code not windows as you tagged. Jun 5, 2017 · You didn't change EAX, and like you said, the register EAX hasn't changed. stack 4096 ExitProcess proto,dwExitCode:dword . Here's a simple example in x86 Assembly that shows these registers in action: Sep 7, 2013 · The thing you want is pretty simple, but you need to add few additional information to your code, because you're writing x86 assembly and not any high-level language like Java or C#. The reason the %eax gets away with this is that OP is copying this from somewhere else (ie not extended asm). You are given eax = 0x5. Oct 11, 2014 · I have been tasked with writing a MASM x86 assembly program which multiplies/divides two 16 bit numbers by bit shifting. inc library to print my result, just use your own method to print. Example: Assume that Initially eax= 0x15DBCB19. You are just lucky that the other 3 match. Oct 31, 2024 · We also used eax = 3 for the sys_read system call and ebx = 0 for the stdin File Descriptor. f bytes as REX prefixes instead of 1 byte encodings of inc/dec. gcc -m32 -O3 -masm=intel -fno-omit-frame-pointer -S -o- source. It is pointless to ;;CLEAR ALL REGISTERS before you move anything to them but be sure to clear EDX before div val2 ;;CALCULATE VAL3/VAL2 because the instruction DIV expects its dividend in 64bit register pair EDX:EAX. Jan 22, 2020 · If you're writing assembly, does it matter which registers you allocate values to? For 80x86; cases where it can matter which register/s you use include: complying with someone else's calling conventions (passing values in the right registers, avoiding stack use for "callee saved" by preferring "caller saved" registers) Jun 21, 2016 · . Just use eax,ebx,ecx,edx. c to have assembly code for source. Mar 26, 2016 · I always thought that ecx is used mainly for loop counter (well, it's called "counter register" for a reason) and I'm not sure why is it used for WriteLine() function, even though eax and ebx are free. c printed to the terminal in Intel syntax, which is the style of assembly you seem to be using. The official documentation manuals from Intel are well over a thousand pages long. mul ebx The eax is implicit. Therefore, after executing your application on a terminal, issuing this command: Jul 7, 2017 · If you allow that to count, then or rax, 0x1234 modifies only eax half, leaving the upper half of rax unchanged There's nothing like mov eax, ebx that modifies only upper half of RAX the way mov ah, 1 modifies the upper half of AX. a: mov ecx, eax ; Temporarily store LowDividend in ECX mov eax, edx ; First divide the HighDividend xor edx, edx ; Setup for division EDX Jul 10, 2019 · You're disassembling 64-bit code as if it were 32-bit code. Write an assembly code that does the following: eax = (ecx + edx ) - (eax + ebx) 2) Write a piece of code that copies the number inside al to ch. Simple example: EAX = 0x8000; ECX = 2; Now, calculate: EAX + 1 = 0x8001 Please write the equivalent assembly code using mov and arithmetic instructions: push %eax pop %ebx Your solution’s ready to go! Our expert help has broken down your problem into an easy-to-learn solution you can count on. It's the kernel that will check value of eax after you invoke it with int 0x80. model flat,stdcall . ebx = 1: File descriptor for standard output Nov 11, 2022 · eax, ebx, ecx and so on are actually registers, which can be seen as "hardware" variables, somewhat similar to higher level-language's variables. Sep 4, 2013 · @chintans Well, I would suggest converting the inline asm to plain C++ code, and see if crash disappears (or debug if it does not). The code does not use ebp so no need to set it up or save it. inc" asm_main: enter 0,0 pusha mov eax, 0 mov ebx, 0 call read_int push eax call functionA add esp, 4 ; or pop something to remove the parameter popa mov eax, 0 ; to return a value to "driver. Store this value in a variable called 'arrayLength'. As my observation, they often showed up on my environment with the sequence of %ecx, %edx and then %eax to store the local variables or other temporary variables. inc ;may remove this and use your own thing . Value in memory at address 0x10C is 0x11. Use a word like "puts" or "places" to avoid using "store", which has a technical meaning in this context. My big problem if that operanda and operandb are representable in 16-byte (4 d-word). But normally I wont need the four lines starting with mov eax,ebx. g. I use NASM: BITS 16 mov al, 0x41 ; hex code for 'A' mov ebx, 0xB8000 ; text screen video memory mov byte [ebx], al ; write 'A' into video memory ; hlt machine end: hlt jmp end ; MBR signature times 510-($-$$) db 0 db 0x55, 0xAA May 11, 2017 · MOVZX EAX,BYTE PTR DS:[EDI] would be like. data mesg db 'KingKong',0xa size equ $-mesg root@bt:~/Arena# nasm -f elf a. Move the contents of the variable 'left' into the EAX register. eax = *(unsigned char *)(regs. Now u should specify how NASM assembly should compare them. data Assume that you are given values in eax, ebx, ecx. The result is still in EAX. In our case it is a c function which prints the result of eax. (When you can't, you can't, but this case it is easy to avoid). Jul 3, 2022 · Use gcc -m32 -fno-pie -Og for a C function that does what you want with a global array. You could covert it to ASCII decimal, or hexadecimal, or any other EBX: The base register, frequently utilized for base pointers in memory accesses. For example, to multiply eax with ebx, placing the result in ecx, you'd do. Nov 28, 2023 · I'm working on a small piece of i386 assembly code and encountered a segmentation fault when using the %ebx register. asm root@bt:~/Arena# ld -e _start -o out a. A Dec 11, 2015 · terminology: reading from memory (add eax, [a]) is a "load". Apr 5, 2023 · . Mar 30, 2010 · EAX: "Extended Accumulator" - used for arithmetic and logical operations, as well as for storing return values from functions. Apr 7, 2015 · @locust Those commands are not meant for a debugger sorry, i was just giving you a way to check your programs return value after running it, that's why i didn't make this an answer, the commands are meant for a terminal, you run the echo commands after you run your program in the same terminal and they will show you your programs return code. Is this just a trick question? Nov 18, 2018 · For example, when you write a function called by other people's code, it is expected that you return the result of your function in eax and preserve the contents of the registers ebx, esi, edi, esp, and ebp. EDX: The data register, often involved in input/output operations. You can get rid of one to make your code shorter: Jan 16, 2009 · I assume you mean x86 assembly and the string is null terminated. Write a piece of code that copies the number inside al toch. Edit your question and try it out. long 18 . 8X",10,0 Nov 27, 2014 · %eax just is an expression that refers to the register called eax. see [here][3] mov eax, [ebx] ; Move the 4 bytes in memory at the address contained in EBX into EAX and the difference explained here: What is the difference between MOV and LEA Nov 15, 2016 · To use if statement in NASM assembly first line should write: comp eax, ebx In this line NASM understands that it should compare two registers. data day WORD 0 month WORD 0 year WORD 0 prompt1 BYTE "enter month: ",0 prompt2 BYTE "enter day: ",0 prompt3 BYTE . My question is that assume adc instructions are not allowed, then how can we write instructions that produce the exact same behaviour as adc eax, ebx. GCC made me some assembly code, and inside theres this statement: lea eax, [ebx+eax] (Intel Syntax) Just curious, what would the difference between that, and: add eax, ebx Be? eax, and ebx con Question: 1) Assume that you are given values in eax, ebx, ecx. notlowercase cmp dl, 'z' ja . Jun 19, 2019 · The same applies here. I will delete them when I see the value in ebx is Nov 17, 2015 · mov eax, 100 mov ebx, 200 mov ecx, 300 add eax, ebx add eax, ecx This would be akin to: int eax = 100; int ebx = 200; int ecx = 300; eax = eax + ebx; /* add EBX to EAX */ eax = eax + ecx; /* add ECX to EAX */ Which would result in a value of 600 in EAX. Move the contents of the variable 'right' into the EBX register. Even if I started to write this paragraph in a different way, %eax is not the same as 0x100, even if the register %eax contains the value 0x100. Note that you have two parallel counters in n and ecx. Nov 8, 2013 · you can use : kilobyte: mov eax, [input] cdq mov ebx, 1024 idiv ebx mov [input], eax So, input now contains the result of idiv. I have two versions of a very simple assembly function. Once the count is zero I move ecx into the sum. I'm arguing that you should delete the footnote, because it's more confusing than helpful. If you had something else in memory after sign those bytes could very well no longer be zero. Also, I see some syntax as movl 8(%ebp), %eax Could some someone suggest me some good reference? 64bit: useless REX prefix jz . I am not asking for the answer to not have 'explode_bomb' ever run. I came across a line that has. Let's say EBX = 2 and you end up with ESI = 6. c" leave ret functionA: mov eax, [esp + 4] call print_int call print_nl mov ebx, 1024 ;segmentation fault occurs here (??? movl a, %eax movl b, %ebx cmpl %ebx, %eax jge L1 movl %eax, %ecx jmp L2 L1: movl %ebx, %ecx L2: movl %ecx, c Write the C code which is equivalent to the above assembly language code. cmp eax, ebx ( comparing both operands) jnae L1 (not to jump above equal) mov eax, ebx (copying data ) L1: cmp ecx, eax . You are given Write one line of code in assembly to Zero eax. Whereas this: mov eax, [ebx] dereferences the contents of ebx and stores the pointed-to value in eax. I would appreciate some insights into why this is happening. Not sure if you are confused about mov eax,1 actually exiting, it doesn't, it just loads 1 into eax. Finally, you could write: mov ebx, 1 and ebx, eax Sep 29, 2020 · I have googled enough but could not figure out what the bracket means. Question: Write a simple assembly code where you count from from eax to ebx. You can find the Linux System Call table here. notlowercase inc ecx . Nov 12, 2015 · I understand where you are coming from, however 1. data array DWORD 0,2,5,9,10 . Apr 17, 2015 · If you are using extended asm (which OP is as indicated by the %1), you MUST use %%ebx. You should have done some test by yourself before posting quesetions. pointer to buffer (esp) in ecx, this you have right Jan 21, 2016 · The interrupt handler for int 0x80 in the operating system expects the function code in eax so that's where you should put it. I am asking for clarification/guidance on what is happening in a small segment of code. Write a program that counts from the value in eax to the value in ebx. 32bit_mode: xor ebx,ebx mov eax, 1 ; exit(0) int 0x80 BITS 64 . Oct 31, 2024 · How to Write Efficient Assembly Code: A Comprehensive Guide Welcome, fellow programmers! Today, we're diving deep into the world of assembly language. Including a "\0" in an immediate doesn't work; that's why you xor eax,eax and push eax where we want some zeros, or use push imm8. Finally, in printOut : Question: After running the Assembly language code below, what are the correct values of EAX, EBX, ECX? mov eax, 11119999h mov ebx, 12340909h mov ecx, 22223333h push eax push ebx push ecx pop bx pop ax pop cx pop cx pop bx pop ax EAX= 12341111 EBX= 12342222 ECX= 2222 1234 EAX= 11111234 EBX= 12349999 ECX=99991234 EAX= 111111111 EBX= 12349999 ECX= 2222 1234 EAX= Please code in x86 assembly language . You are given Jan 21, 2016 · The interrupt handler for int 0x80 in the operating system expects the function code in eax so that's where you should put it. Question: After running the Assembly language code below, what are the correct values of EAX, EBX, ECX? mov eax, 11119999h mov ebx, 12340909h mov ecx, 22223333h push eax push ebx push ecx pop cx pop bx pop ax pop ax pop cx pop bx Question 5 options: EAX= 11111111 EBX=12349999 ECX= 22229999 Apr 12, 2015 · The long way to find the sum of gaps:. Write a simple assembly code where you count from from eax to ebx. notdigit: cmp dl, 'a' jb . cmp %eax, (%ebx) Now, is there a difference when comparing these two registers, since one has parenthesis around it? The book I have does not do a great job of explaining this. Jul 12, 2017 · Now I want to ask about how is this code working behind the scenes. Write a piece of code that copies the number inside al to ch. When I use the %ecx register, the function works correctly. From what I understand I am making room for two long values in the x section and room for the sum of the count. This is not normally possible unless you specifically override your disassembler or use objcopy or something to copy 64-bit machine-code into a 32-bit ELF object file. I didn't want to decrease the chances of anyone bothering to answer my question by obscuring it with my own thoughts and attempts over the past 2-3 hours. ECX: "Extended Counter" - often used for loop and string operations, as well as for storing function arguments. So if you really want to print %eax, you need to first convert that integer to a sequence of characters. Your solution’s ready to go! Our expert help has broken down your problem into an easy-to-learn solution you can count on. Click the orange question mark in the editor toolbar for more information and tips on formatting. code MAIN PROC MOV EAX, 0 ; or XOR EAX, EAX - sets eax to 0 MOV ECX, 100 ; loop counter - our loop will run 100 times myloop: ADD EAX, ECX ; adds ECX to EAX loop myloop call writedec Dec 11, 2016 · section . data LookUpDig db "0123456789" ; Translation Table PIDString db "PID: " PIDLength equ $-PIDString SECTION . 1. Apr 3, 2014 · I used the i r command in gdb to show the stack content, and learned that ebx is my input value, and eax is 134522400. May 13, 2012 · Note you can format lines as code by indenting them four spaces. like After running the Assembly language code below, what are the correct values of EAX, EBX, ECX? mov eax, 11119999h mov ebx, 12340909h mov ecx, 22223333h push eax push ebx push ecx pop ax pop bx pop cx pop cx pop ax pop bx Sep 5, 2018 · a normal requirement for shellcode is that the machine code not contain any 00 bytes, so strcpy doesn't stop when overflowing a buffer. The x86 instruction set is largely designed around machine instructions that let you specify one register and one memory operand, because that is pretty useful, and it doesn't affect performance of operations that fetch to register and then put to memory in separate steps. data format: db "result = %8. data ;data segment msg db 'Hello, world!',0xa ;our dear string Answer to Do the following problems: a. bss buffer resb 64 section . text _start: mov eax, 4 mov ebx, 1 mov ecx, mesg mov edx, size int 0x80 exit: mov eax, 1 int 0x80 section . For example, a simple assembly function can be: #include "stdio. First of all, mask in your code is not declared in your function. It's nasm syntax. Dec 12, 2023 · (You also have to consider whether you are allowed to modify EBX, I would think that usually in the context of a code snippet, the answer would be yes, here since BX already has a value of interest. Jul 22, 2023 · Prologue and epilogue are not required. Processing: The tool looks at your input using advanced methods and language patterns, turning your needs into working assembly code. Output: In the end, the AI shows you the generated assembly code, ready for use or further development. That because the result saved in EBX. And on the fact that the fd=0 stdin file descriptor refers to the same read-write file description when you run your program on a Sep 21, 2017 · mov ebx, eax ; put exit code into ebx mov eax, 1 ; exit sys call int 0x80 section . Nov 16, 2016 · In your particular case: edx = 3, eax = 0x100, temporary_address_in_CPU_during_mov = eax + edx * 4 = 0x100 + 3*4 = 0x10C. Your code must be as efficient as possible. text segment . Write an assembly code that does the following: eax = (ecx + edx ) - (eax + ebx) е 2. Than I insert 5 into eax and 10 into ebx and the value of x which will be count into ecx. notdigit cmp dl, '9' ja . So, I have changed the code to this and it's giving me false too(je didn't work and jne work): cmp eax, 1 je VolumeSphere Eax must contain 1, coz it definitely points to place in memory, where I write/read from file value Nov 2, 2012 · lea eax, [var] — the address of var is placed in EAX. o ld Aug 17, 2011 · bits 32 extern printf global main section . The "{}" button in the editor toolbar does this for you. Use gdb debugger. Jan 6, 2015 · Is this expression allowed in Assembly: mov eax, [(ebp + 8) + [ebp - 25]] And if it is allowed, does this is what it evaluates to: (ebp + 8) evaluates to an address, this address is then added to the memory value pointed to by (ebp - 25) , and then this summed value is used itself as an address and the value pointed by this new address is moved Jul 14, 2020 · Env: i386 32-bit Assembly: AT&T OS: Linux. For gcc I advice you to type. Example: Assume that Initially eax =0×15DBCB19. You need to May 19, 2014 · If you have decided to use a frame pointer, the usual thing to do is save them after setting up ebp. 64bit_mode ; uncomment to test that the 64bit code does fault in a 32bit binary . Apr 20, 2019 · On UNIX-like systems such as Linux, you can use the -S option to generate assembly code. aslxf egq twba cmrmmd kyfyhv dlaptg fvyo ezqb vwyqrigr pwruf