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  • How to determine values saved on the stack?

    - by Brian
    I'm doing some experimenting and would like to be able to see what is saved on the stack during a system call (the saved state of the user land process). According to http://lxr.linux.no/#linux+v2.6.30.1/arch/x86/kernel/entry_32.S it shows that the various values of registers are saved at those particular offsets to the stack pointer. Here is the code I have been trying to use to examine what is saved on the stack (this is in a custom system call I have created): asm("movl 0x1C(%esp), %ecx"); asm("movl %%ecx, %0" : "=r" (value)); where value is an unsigned long. As of right now, this value is not what is expected (it is showing a 0 is saved for the user value of ds). Am I correctly accessing the offset of the stack pointer? Another possibility might be could I use a debugger such as GDB to examine the stack contents while in the kernel? I don't have much extensive use with debugging and am not sure of how to debug code inside the kernel. Any help is much appreciated.

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  • Writing a VM - well formed bytecode?

    - by David Titarenco
    Hi, I'm writing a virtual machine in C just for fun. Lame, I know, but luckily I'm on SO so hopefully no one will make fun :) I wrote a really quick'n'dirty VM that reads lines of (my own) ASM and does stuff. Right now, I only have 3 instructions: add, jmp, end. All is well and it's actually pretty cool being able to feed lines (doing it something like write_line(&prog[1], "jmp", regA, regB, 0); and then running the program: while (machine.code_pointer <= BOUNDS && DONE != true) { run_line(&prog[machine.cp]); } I'm using an opcode lookup table (which may not be efficient but it's elegant) in C and everything seems to be working OK. My question is more of a "best practices" question but I do think there's a correct answer to it. I'm making the VM able to read binary files (storing bytes in unsigned char[]) and execute bytecode. My question is: is it the VM's job to make sure the bytecode is well formed or is it just the compiler's job to make sure the binary file it spits out is well formed? I only ask this because what would happen if someone would edit a binary file and screw stuff up (delete arbitrary parts of it, etc). Clearly, the program would be buggy and probably not functional. Is this even the VM's problem? I'm sure that people much smarter than me have figured out solutions to these problems, I'm just curious what they are!

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  • C++ from SpeakHere in iPhone app

    - by niklassaers
    Hi guys, I've made a template app where I've grabbed the recording part of the SpeakHere example and removed the file handling part, but I'm struggeling to get the C++ part of the app working right. As soon as it enters the C++ class, it gets syntax errors. If I don't import the header files from C++ (and then of course don't use the code) into my Objective C classes, all works fine. I cannot see the difference between how I'm doing it and the example is doing it. Can you see the difference? I've posted the entire code here: http://github.com/niklassaers/testFFT The build errors I get are: testFFT/CAStreamBasicDescription.h:91:0 testFFT/CAStreamBasicDescription.h:91: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'CAStreamBasicDescription' testFFT/CAStreamBasicDescription.h:298:0 testFFT/CAStreamBasicDescription.h:298: error: expected '=', ',', ';', 'asm' or '__attribute__' before '<' token testFFT/CAStreamBasicDescription.h:299:0 testFFT/CAStreamBasicDescription.h:299: error: expected '=', ',', ';', 'asm' or '__attribute__' before '==' token testFFT/CAStreamBasicDescription.h:301:0 testFFT/CAStreamBasicDescription.h:301: error: expected '=', ',', ';', 'asm' or '__attribute__' before '!=' token testFFT/CAStreamBasicDescription.h:302:0 testFFT/CAStreamBasicDescription.h:302: error: expected '=', ',', ';', 'asm' or '__attribute__' before '<=' token testFFT/CAStreamBasicDescription.h:303:0 testFFT/CAStreamBasicDescription.h:303: error: expected '=', ',', ';', 'asm' or '__attribute__' before '>=' token testFFT/CAStreamBasicDescription.h:304:0 testFFT/CAStreamBasicDescription.h:304: error: expected '=', ',', ';', 'asm' or '__attribute__' before '>' token testFFT/CAStreamBasicDescription.h:307:0 testFFT/CAStreamBasicDescription.h:307: error: expected ';', ',' or ')' before '&' token testFFT/CAXException.h:65:0 testFFT/CAXException.h:65: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'CAX4CCString' testFFT/CAXException.h:87:0 testFFT/CAXException.h:87: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'CAXException' testFFT/AQRecorder.h:59:0 testFFT/AQRecorder.h:59: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'AQRecorder' testFFT/RecorderLink.h:57:0 testFFT/RecorderLink.h:57: error: expected specifier-qualifier-list before 'AQRecorder' testFFT/RecorderLink.h:62:0 testFFT/RecorderLink.h:62: error: expected specifier-qualifier-list before 'AQRecorder' Any idea what's going on here? Cheers Nik

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  • How to get HP ASM to work under Xen Hypervisor?

    - by Dennis
    I have a HP DL560, currently running Debian Squeeze as dom0 on Xen Hypervisor, and the fans constantly run at 100%. In the past this wasn't a problem because I could install HP's ASM which includes fan management. However since I have installed a xen enabled kernel, the hp-health driver (the piece of ASM that controls the fans) won't start (at boot or manually). Anyone know of any way to make it work? (Or any other method of controlling the fans safely.) Note that the server has four i386 Xeon CPUs, each with its own fan, plus an extra case fan, and all of the fans can be doubled for redundancy. Also everything works fine under Squeeze without the xen-enabled kernel (can still boot the other one and hp-health loads fine on boot).

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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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  • Passing parameters 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 that 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 (SP)+, D0 |get 1st parameter, put in D0 MOVE.L (SP)+, D2 |get 2nd parameter, put in D2 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 do you find a functions virtual call address in assembly?

    - by Daniel
    I've googled around but i'm not sure i am asking the right question or not and i couldn't find much regardless, perhaps a link would be helpful. I made a c++ program that shows a message box, then I opened it up with Ollydbg and went to the part where it calls MessageBoxW. The call address of MessageBoxW changes each time i run the app as windows is updating my Imports table to have the correct address of MessageBoxW. So my question is how do i find the virtual addres of MessageBoxW to my imports table and also how can i use this in ollydbg? Basically I'm trying to make a code cave in assembly to call MessageBoxW again. I got fairly close once by searching the executable with a hex editor and found the position of the call, and I think I found the virtual address. But when i call that virtual address in olly and saved it to the executable, the next time i opened it the call was replaced with a bunch of DB xyz (which looked like the virtual address but why did the call get removed? Sorry if my terminology is off as i'm new to this so i'm not quite sure what to call things.

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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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  • i386 assembly question: why do I need to meddle with the stack pointer?

    - by zneak
    Hello everyone, I decided it would be fun to learn x86 assembly during the summer break. So I started with a very simple hello world program, borrowing on free examples gcc -S could give me. I ended up with this: HELLO: .ascii "Hello, world!\12\0" .text .globl _main _main: pushl %ebp # 1. puts the base stack address on the stack movl %esp, %ebp # 2. puts the base stack address in the stack address register subl $20, %esp # 3. ??? pushl $HELLO # 4. push HELLO's address on the stack call _puts # 5. call puts xorl %eax, %eax # 6. zero %eax, probably not necessary since we didn't do anything with it leave # 7. clean up ret # 8. return # PROFIT! It compiles and even works! And I think I understand most of it. Though, magic happens at step 3. Would I remove this line, my program would die between the call to puts and the xor from a misaligned stack error. And would I change $20 to another value, it'd crash too. So I came to the conclusion that this value is very important. Problem is, I don't know what it does and why it's needed. Can anyone explain me? (I'm on Mac OS, would it ever matter.)

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  • C2244 when trying to call the pow function from inline assembly

    - by schrödingers cat
    I would like to call the pow function from inline assembly. The problem is i'm getting error C2244: 'pow' : unable to match function definition to an existing declaration. I'm new to assembly so this may be a trivial question but how do i resolve this? I guess it has something to do with the compiler not beeing able to properly resolve the overload of pow. The following code fragment is causing the error: do_POW: // push first argument to the stack sub esp, size value_type fld qword ptr [ecx] fstp qword ptr [esp] // push second argument to the stack sub esp, size value_type fld qword ptr [ecx - size value_type] fstp qword ptr [esp]and pop fpu stack // call the pow function call pow sub ecx, size value_type fstp qword ptr [ecx] add esp, 2 * size value_type jmp loop_start

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  • How to get information from objdump

    - by Summer_More_More_Tea
    I encounter a problem when reading information dumped out from an executable file in linux. The information is as follows: 804a0ea: 04 08 add $0x8, %al ... 804a0f4: a6 cmpsb %es:(%edi),%ds:(%esi) I have two questions: what does the address 804a0ea and 804a0f4 mean? the virtual address in the process's address space? what does the ... mean? how can I get instruction at address 804a0f0? Thanks in advance.

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  • How to use MOV instruction in ARM with an immediate number as the second operand

    - by Summer_More_More_Tea
    Hi everyone: I just begin to study ARM assembly language, and am not clear about how to use MOV to transfer an immediate number into a register. From both the ARM reference manual and my textbook, it's said that range of immediate number following MOV instruction is 0-255. But when I test on my own PC in ADS 1.2 IDE, instruction MOV R2, #0xFFFFFFFF performs well. Isn't number 0xFFFFFFFF out of range according to the specification? Hope someone can give me a hand. Regards.

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  • Assembly Programming on Mac

    - by ida
    I am on a Mac with Snow Leopard (10.6.3). I hear that the assembly language I work with has to be valid with the chipset that you use. I am completely new to this I have a basic background in C and Objective-C programming and an almost strong background in PHP. I have always wanted to see what assembly is all about. The tutorial I'll be looking at is by VTC [link]. What I want to know is: are the tutorials that I'm about to do compatible with the assembly version on the Mac that I have? Sorry I am completely new to this language although I do recall studying some of it way, way back in the day. I do have xcode and what I'm wondering is what kind of document would I open in xcode to work with assembly and does the Mac have a built in hex editor (when it comes time to needing it)? thanks

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  • changing bin code a bit

    - by oneat
    If in exe (written in c++) file in .text section I'll add instruction like push eax; pop eax; I mean something what won't change anything. Will this program work properly or everything would get crashed ?

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  • How can I go about writing to the console in fasm?

    - by codinggoose
    The code I currently have can be found at: http://fasm.pastebin.com/yY3C0aVF I'm exceptionally new to assembly, only picked it up yesterday and I've looked through many an example and still can't figure out for myself how to write to the console. I always get an error when I seem to replicate it in my own way. If I'm not on the right track at all please let me know, also if you can suggest a good book on fasm it would be greatly appreciated.

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  • how to make struct member pointer in assembly?

    - by sillis
    I`m trying to create a macro which would make easier to point to a structs member. Currently i am pointing to a structs member in assembly file using the STRUCT_NAME + offset method. For example if i want to point structs third member,i would have to do it like this: STRUCT_NAME + 3. This seems stupid way to do it, and if i insert more members in the struct, i have to update all the offset values in the code. Is there a way to point using STRUCT_NAME + macro(struct_name, member_name) ? I`m using texas instruments TMS320C28x hardware. Thanks!

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  • C#: Hijacking a near relative call

    - by Lex
    Alright, I'm trying to write a vary basic modification to a program NOT written by me. I DO NOT have the source to it. I also do not care if this only works for a single version of the program, so hard coding offsets is feasible. Anyways, I've found the function and where it is called in the compiled program. .text:1901C88F loc_1901C88F: ; CODE XREF: ConnectionThread+1A2j .text:1901C88F ; DATA XREF: .text:off_1901CC64o .text:1901C88F 8B C8 mov ecx, eax ; jumptable 1901C862 case 11 .text:1901C891 8B C6 mov eax, esi .text:1901C893 E8 48 C5 FF FF call ChatEvent According to IDA the full function signature is: char *__usercall ChatEvent<eax>(char *Data<eax>, unsigned int Length<ecx>) I already have all I need to patch the program during runtime, and do whatever other manipulations I need. What I need, is to be able to write a function like so: bool ProcessChat(char *Data, unsigned int Length); char *__usercall HijackFunction(char *Data, unsigned int Length){ if (ProcessChat(Data, Length)) Call OriginalChatEvent(Data, Length); } Get the jist of what I am trying to do? With stdcall function it's easy just replace the 4 byte address with my own function's address. But this is a near relative call, which is.. more annoying. So, anyone have any idea?

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