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  • MIPS assembly: big and little endian confusion

    - by Barney
    I've run the following code snippet on the MIPS MARS simulator. That simulator is little endian. So the results are as follows: lui $t0,0x1DE # $t0 = 0x01DE0000 ori $t0,$t0,0xCADE # $t0 = 0x01DECADE lui $t1,0x1001 # $t1 = 0x10010000 sw $t0,200($t1) # $t1 + 200 bytes = 0x01DECADE lw $t2,200($t1) # $t2 = 0x01DECADE So on a little endian MIPS simulator, the value of $t2 at the end of the program is 0x01DECADE. If this simulator was big endian, what would the value be? Would it be 0xDECADE01 or would it still be 0x01DECADE?

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  • [Assembly] jnz after xor?

    - by kotarou3
    After using IDA Pro to disassemble a x86 dll, I found this code (Comments added by me in pusedo-c code. I hope they're correct): test ebx, ebx ; if (ebx == false) jz short loc_6385A34B ; Jump to 0x6385a34b mov eax, [ebx+84h] ; eax = *(ebx+0x84) mov ecx, [esi+84h] ; ecx = *(esi+0x84) mov al, [eax+30h] ; al = *(*(ebx+0x84)+0x30) xor al, [ecx+30h] ; al = al XOR *(*(esi+0x84)+0x30) jnz loc_6385A453 Lets make it simpler for me to understand: mov eax, b3h xor eax, d6h jnz ... How does the conditional jump instruction work after a xor instruction?

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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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  • C/C++/Assembly Programatically detect if hyper-threading is active on Windows, Mac and Linux

    - by HTASSCPP
    I can already correctly detect the number of logical processors correctly on all three of these platforms. To be able to detect the number of physical processors/cores correctly I'll have to detect if hyperthreading is supported AND active (or enabled if you prefer) and if so divide the number of logical processors by 2 to determine the number of physical processors. Perphaps I should provide an example: A quad core Intel CPU's with hyperthreading enabled has 4 physical cores, yet 8 logical processors (hyperthreading creates 4 more logical processors). So my current function would detect 8 instead of the desired 4. My question therefore is if there is a way to detect whether hyperthreading is supported AND ENABLED?

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  • Attempting to convert an if statement to assembly

    - by Malfist
    What am I doing wrong? This is the assmebly I've written: char encode(char plain){ __asm{ mov al, plain ;check for y or z status cmp al, 'y' je YorZ cmp al, 'z' je YorZ cmp al, 'Y' je YorZ cmp al, 'Z' je YorZ ;check to make sure it is in the alphabet now mov cl, al sub cl, 'A' cmp cl, 24 jl Other sub cl, '6' ;there are six characters between 'Z' and 'a' cmp cl, 24 jl Other jmp done ;means it is not in the alphabet YorZ: sub al, 24 jmp done Other: add al, 2 jmp done done: leave ret } } and this is the C code it's supposed to replace, but doesn't char encode(char plain){ char code; if((plain>='a' && plain<='x') || (plain>='A' && plain <='X')){ code = plain+2; }else if(plain == 'y' || plain=='z' || plain=='Y' || plain == 'y'){ code = plain - 24; }else{ code = plain; } return code; } It seems to convert every character that isn't an y,z,Y,Z into a plus 2 equivalent instead of just A-Xa-x. Any ideas why?

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  • Visual C++ Assembly link library troubles

    - by Sanarothe
    Hi. I'm having a problem having my projects built in VC++ Express 2008... I'm using a library, irvine32.inc/lib. INCLUDE Irvine32.inc works for me at school (On already configured VS environments) by default, but at home (Windows 7 x64) I'm having a boatload of issues. My original post here was that a file that irvine32.inc referenced, in the same folder, 'could not be opened.' Added irvine folder to the include path for specific project, progress. Then I was getting an error with mt.exe, but a suggestion on the MSDN suggested turn off antivirus, and now project does build but when I run a program that does NOT reference anything in irvine32, it tells me repeatedly that my project has triggered a breakpoint, and allows me to continue or break. Continue just pops the same window, break loads another popup telling me that "No symbols are loaded for any call stack frame. Source code cannot be displayed." This popup lets me view the disassembly. I tested it with and without working statements, it just throws the same breakpoint on the first line of code. Now, if I run the program when it DOES require something from the include file, in this case, DumpRegs: INCLUDE Irvine32.inc .data .code main PROC mov ebx,1000h mov eax,1000h add eax,ebx call DumpRegs main ENDP END main This gives me 1main.obj : error LNK2019: unresolved external symbol _DumpRegs@0 referenced in function _main@0 1C:\Users\Cameron\csis165\Lab8_CCarroll\Debug\Lab8_CCarroll.exe : fatal error LNK1120: 1 unresolved externals This does NOT happen when I build a project from the book author's examples, which has the same include statement. I'm baffled. :(

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  • Assembly: compile a COM program

    - by Fantomas
    Hi! Can COM program be 32 bit? How can I compile COM program? I have TLINK32 and TASM32. tasm32 \t alex_7.asm pause tlink32 alex_7.obj pause td32 main.exe I ve got following error: Fatal: 16 bit segments not supported in module alex_7.asm I have DOSBOX and I'am running Windows 7 x64 I got same when I try to compile my program inside DOSBOX

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  • Can you help with this assembly language code?

    - by Mugen
    Hi, I've been looking through a piece of code of a pc game that I'm trying to "improve". (ok so maybe I suck at the game but I still want to play it). Could you please look into the following code: fld dword ptr[ebp+00007B1C] fsub dword ptr[esp+64] fst dword ptr[ebp+00007B1C] call 004A2E48 This code is called every second for the level countdown timer. I need to stay on a particular level for a few minutes. If I can modify the above code so that the value pushed into the address [ebp+00007B1C] is 0 then the game level will always time out and it will save me playing those crazy "survival" minigames. I'll explain what I understand from this code. Dont worry, you dont have to go deep into this. In the first line we get the timer value. For example if 97 seconds are remaining then it is here that this value is loaded. In the second line a value (1 second) is subtracted from 97. In the third line 96 is again moved to memory. And finally we have the function call that will do other processing based on the time remaining. Now all I need to do is patch this piece of code somehow so that the value that is pushed is 0 (in the third step). Can you please help me out with this?

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  • Illegal instruction in Assembly

    - by Natasha
    I really do not understand why this simple code works fine in the first attempt but when putting it in a procedure an error shows: NTVDM CPU has encountered an illegal instruction CS:db22 IP:4de4 OP:f0 ff ff ff ff The first code segment works just fine: .model small .stack 100h .code start: mov ax,@data mov ds,ax mov es,ax MOV AH,02H ;sets cursor up MOV BH,00H MOV DH,02 MOV DL,00 INT 10H EXIT: MOV AH,4CH INT 21H END However This generates an error: .model small .stack 100h .code start: mov ax,@data mov ds,ax mov es,ax call set_cursor PROC set_cursor near MOV AH,02H ;sets cursor up MOV BH,00H MOV DH,02 MOV DL,00 INT 10H RET set_cursor ENDP EXIT: MOV AH,4CH INT 21H END Note: Nothing is wrong with windows config. I have tried many sample codes that work fine Thanks

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  • Assembly stack persistency

    - by user246100
    Hello. I would like to know if after calling functions the data I have in the stack is persistent. Like, I would like to know if (assuming cdecl convention) can I do this (independently of function X and independently of optimizations): push 1 push 2 push 3 call X call X call X add 12 esp ? Also, let's say that before the calls I save the address of where the pushed values are in a global variable. Can I, inside X, alter the values it contain by acessing the global variable? Like, for some reason I want that in X I'm able to alter the values in stack so that the second and third call to X receive different values.

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  • For Loops in MIPS assembly

    - by John Moffitt
    I'm having problems getting my processor to simulate correctly and I think I've narrowed it down to the program I'm giving it. 1. li $R1, 0 2. li $R2, 0x100 3. li $R6, 1 4. li $R8, 0 5. li $R9, 20 6. lw $R3, 0($R1) 7. lw $R4, 4($R1) 8. add $R5, $R3, $R4 9. srlv $R5, $R5, $R6 10. sw $R5, 0($R2) 11. addi $R1, $R1, 4 12. addi $R2, $R2, 4 13. addi $R8, $R8, 1 14. slt $R7, $R8, $R9 15. bnq $R7, $zero, -9 It should iterate through the bottom portion 20 times and then exit. I'm particularly unsure about the branch instruction but I can't find anything wrong with it so : /

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  • x86 Assembly Question about outputting

    - by jdea
    My code looks like this _declspec(naked) void f(unsigned int input,unsigned int *output) { __asm{ push dword ptr[esp+4] call factorial pop ecx mov [output], eax //copy result ret } } __declspec(naked) unsigned int factorial(unsigned int n) { __asm{ push esi mov esi, dword ptr [esp+8] cmp esi, 1 jg RECURSE mov eax, 1 jmp END RECURSE: dec esi push esi call factorial pop esi inc esi mul esi END: pop esi ret } } Its a factorial function and I'm trying to output the answer after it recursively calculates the number that was passed in But what I get returned as an output is the same large number I keep getting Not sure about what is wrong with my output, by I also see this error CXX0030: Error: expression cannot be evaluated Thanks!

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  • Intel Assembly Programming

    - by Kay
    class MyString{ char buf[100]; int len; boolean append(MyString str){ int k; if(this.len + str.len>100){ for(k=0; k<str.len; k++){ this.buf[this.len] = str.buf[k]; this.len ++; } return false; } return true; } } Does the above translate to: start: push ebp ; save calling ebp mov ebp, esp ; setup new ebp push esi ; push ebx ; mov esi, [ebp + 8] ; esi = 'this' mov ebx, [ebp + 14] ; ebx = str mov ecx, 0 ; k=0 mov edx, [esi + 200] ; edx = this.len append: cmp edx + [ebx + 200], 100 jle ret_true ; if (this.len + str.len)<= 100 then ret_true cmp ecx, edx jge ret_false ; if k >= str.len then ret_false mov [esi + edx], [ebx + 2*ecx] ; this.buf[this.len] = str.buf[k] inc edx ; this.len++ aux: inc ecx ; k++ jmp append ret_true: pop ebx ; restore ebx pop esi ; restore esi pop ebp ; restore ebp ret true ret_false: pop ebx ; restore ebx pop esi ; restore esi pop ebp ; restore ebp ret false My greatest difficulty here is figuring out what to push onto the stack and the math for pointers. NOTE: I'm not allowed to use global variables and i must assume 32-bit ints, 16-bit chars and 8-bit booleans.

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  • assembly language programming (prime number)

    - by chris
    Prompt the user for a positive three digit number, then read it. Let's call it N. Divide into N all integer values from 2 to (N/2)+1 and test to see if the division was even, in which case N is instantly shown to be non-prime. Output a message printing N and saying that it is not prime. If none of those integer values divide evenly (remainder never is zero), then N is shown to be prime. Output a message printing N and saying that it is prime. Ask the user if he or she wants to test another number; if the user types "n" or "N", quit. If "y" or "Y", jump back and repeat. Comments in your code are essential. Hi. I am kinda in rush to do this.. please help me doing it. I'll be much appreciated. thank you

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  • Using different versions of the same assembly in the same folder

    - by Hemanshu Bhojak
    I have the following situation Project A - Uses Castle Windsor v2.2 - Uses Project B via WindsorContainer Project B - Uses NHibernate - Uses Castle Windsor v2.1 In the bin folder of Project A I have the dll Castle.DynamicProxy2.dll v2.2 and NHibernate dlls. Now the problem is that NHibernate is dependent on Castle.DynamicProxy2.dll v2.1 which is not there. How do I resolve this situation.

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  • how to push a string address to stack with assembly, machine code

    - by Yigit
    Hi all, I am changing minesweeper.exe in order to have an understanding of how code injection works. Simply, I want the minesweeper to show a message box before starting. So, I find a "cave" in the executable and then define the string to show in messagebox and call the messagebox. Additionally of course, I have to change the value at module entry point of the executable and first direct it to my additional code, then continue its own code. So at the cave what I do; "hello starbuck",0 push 0 //arg4 of MessageBoxW function push the address of my string //arg3, must be title push the address of my string //arg2, must be the message push 0 //arg1 call MessageBoxW ... Now since the memory addresses of codes in the executable change everytime it is loaded in the memory, for calling the MessageBoxW function, I give the offset of the address where MessageBoxW is defined in Import Address Table. For instance, if MessageBoxW is defined at address1 in the IAT and the instruction just after call MessageBoxW is at address2 instead of writing call MessageBoxW, I write call address2 - address1. So my question is, how do I do it for pushing the string's address to the stack? For example, if I do these changes via ollydbg, I give the immediate address of "hello starbuck" for pushing and it works. But after reloading the executable or starting it outside of ollydbg, it naturally fails, since the immediate addresses change. Thanks in advance, Yigit.

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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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