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  • "Hello World" in less than 20 bytes

    - by xelurg
    We have had an interesting competition once, where everyone would write their implementation of hello world program. One requirement was that is should be less than 20 bytes in compiled form. the winner would be the one whose version is the smallest... What would be your solution? :) Platform: 32bit, x86 OS: DOS, Win, GNU/Linux, *BSD Language: Asm, C, or anything else that compiles into binary executable (i.e. no bash scripts and stuff ;)

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  • Algorithm for finding the smallest power of two that's greater or equal to a given value

    - by Boyan
    I need to find the smallest power of two that's greater or equal to a given value. So far, I have this: int value = 3221; // 3221 is just an example, could be any number int result = 1; while (result < value) result <<= 1; It works fine, but feels kind of naive. Is there a better algorithm for that problem? EDIT. There were some nice Assembler suggestions, so I'm adding those tags to the question.

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  • Working with ieee format numbers in ARM

    - by Jake Sellers
    I'm trying to write an ARM program that will convert an ieee number to a TNS format number. TNS is a format used by some super computers, and is similar to ieee but different. I'm trying to use several masks to place the three different "part" of the ieee number in separate registers so I can move them around accordingly. Here is my unpack subroutine: UnpackIEEE LDR r1, SMASK ;load the sign bit mask into r1 LDR r2, EMASK ;load the exponent mask into r2 LDR r3, GMASK ;load the significand mask into r3 AND r4, r0, r1 ;apply sign mask to IEEE and save into r4 AND r5, r0, r2 ;apply exponent mask to IEEE and save into r5 AND r6, r0, r3 ;apply significand mask to IEEE and save into r6 MOV pc, r14 ;return And here are the masks and number declarations so you can understand: IEEE DCD 0x40300000 ;2.75 decimal or 01000000001100000000000000000000 binary SMASK DCD 0x80000000 ;Sign bit mask EMASK DCD 0x7F800000 ;Exponent mask GMASK DCD 0x007FFFFF ;Significand mask When I step through with the debugger, the results I get are not what I expect after working through it on paper. EDIT: What I mean, is that after the subroutine runs, registers 4, 5, and 6 all remain 0. I can't figure out why the masks are not working. I think I do not fully understand how the number is being stored in the register or using the masks wrong. Any help appreciated. If you need more info just ask. EDIT: entry point: Very simple, just trying to get these subroutines working. ENTRY LDR r1, IEEE ;load IEEE num into r1 BL UnpackIEEE ;call unpack sub SWI SWI_Exit ;finish

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  • Subroutine & GoTo design

    - by sub
    I have a strange question concerning subroutines: As I'm creating a minimal language and I don't want to add high-level loops like while or for I was planning on just adding gotos to keep it Turing-Complete. Now I thought, eww - gotos - I wouldn't want to program in that language if I had to use gotos so often. So I thought about adding subroutines instead. I see the difference as the following: gotos Go to (captain obvious) a previously defined point and continue executing the program from there. Leads to hardly understandable and buggy code, I think that's a fact. subroutines Similiar: You define their starting point somewhere, as you call them the program jumps there - but the subroutine can go back to the point it was called from with return. Okay. Why didn't I just add the more function-like, nice looking subroutines? Because: In order to make return work if I call subroutines from within subroutines from within other subroutines, I'd have to use a stack containing the point where the currently running subroutine came from at top. That would then mean that I would, if I create loops using the subroutines, end up with an extremely memory-eating, overflowing stack with return locations. Not good. Don't think of my subroutines as functions. They are just gotos that return to the point they were called from, they don't actually give back values like the return x; statement in nearly all today's languages. Now to my actual questions: How can I solve the above problem with the stack overflow on loops with subroutines? Do I have to add a separate goto language construct without the return option? Assembler doesn't have loops but as I have seen myJumpPoint:, jnz, jz, retn. That means to me that there must also be a stack containing all the return locations. Am I right with that? What about long running loops then? Don't they overflow the stack/eat memory then? Am I getting the retn symbol in assembler totally wrong? If yes, please explain it to me.

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  • FASM vc MASM trasnlation problem in mov si, offset msg

    - by Ruben Trancoso
    hi folks, just did my first test with MASM and FASM with the same code (almos) and I falled in trouble. The only difference is that to produce just the 104 bytes I need to write to MBR in FASM I put org 7c00h and in MASM 0h. The problem is on the mov si, offset msg that in the first case transletes it to 44 7C (7c44h) and with masm translates to 44 00 (0044h)! but just when I change org 7c00h to org 0h in MASM. Otherwise it will produce the entire segment from 0 to 7dff. how do I solve it? or in short, how to make MASM produce a binary that begins at 7c00h as it first byte and subsequent jumps remain relative to 7c00h? .model TINY .code org 7c00h ; Boot entry point. Address 07c0:0000 on the computer memory xor ax, ax ; Zero out ax mov ds, ax ; Set data segment to base of RAM jmp start ; Jump to the first byte after DOS boot record data ; ---------------------------------------------------------------------- ; DOS boot record data ; ---------------------------------------------------------------------- brINT13Flag db 90h ; 0002h - 0EH for INT13 AH=42 READ brOEM db 'MSDOS5.0' ; 0003h - OEM name & DOS version (8 chars) brBPS dw 512 ; 000Bh - Bytes/sector brSPC db 1 ; 000Dh - Sectors/cluster brResCount dw 1 ; 000Eh - Reserved (boot) sectors brFATs db 2 ; 0010h - FAT copies brRootEntries dw 0E0h ; 0011h - Root directory entries brSectorCount dw 2880 ; 0013h - Sectors in volume, < 32MB brMedia db 240 ; 0015h - Media descriptor brSPF dw 9 ; 0016h - Sectors per FAT brSPH dw 18 ; 0018h - Sectors per track brHPC dw 2 ; 001Ah - Number of Heads brHidden dd 0 ; 001Ch - Hidden sectors brSectors dd 0 ; 0020h - Total number of sectors db 0 ; 0024h - Physical drive no. db 0 ; 0025h - Reserved (FAT32) db 29h ; 0026h - Extended boot record sig brSerialNum dd 404418EAh ; 0027h - Volume serial number (random) brLabel db 'OSAdventure' ; 002Bh - Volume label (11 chars) brFSID db 'FAT12 ' ; 0036h - File System ID (8 chars) ;------------------------------------------------------------------------ ; Boot code ; ---------------------------------------------------------------------- start: mov si, offset msg call showmsg hang: jmp hang msg db 'Loading...',0 showmsg: lodsb cmp al, 0 jz showmsgd push si mov bx, 0007 mov ah, 0eh int 10h pop si jmp showmsg showmsgd: retn ; ---------------------------------------------------------------------- ; Boot record signature ; ---------------------------------------------------------------------- dw 0AA55h ; Boot record signature END

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  • Setting a cell's format using Excel 2007 Interop and C#

    - by CVertex
    I'm using the office 2007 interop assemblies to create some excel spreadsheets. There are plenty of questions on here about getting started and MSDN contains heaps of articles, like this one. The API is funky, and sometimes a bit confusing. When I set a value of a cell, is there a way to set it's format? I'd like to mark particular fields as Date's so my customer can run excel macros on them. Also, numbers would be useful. Thanks!

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  • [ebp + 6] instead of +8 in a JIT compiler

    - by David Titarenco
    I'm implementing a simplistic JIT compiler in a VM I'm writing for fun (mostly to learn more about language design) and I'm getting some weird behavior, maybe someone can tell me why. First I define a JIT "prototype" both for C and C++: #ifdef __cplusplus typedef void* (*_JIT_METHOD) (...); #else typedef (*_JIT_METHOD) (); #endif I have a compile() function that will compile stuff into ASM and stick it somewhere in memory: void* compile (void* something) { // grab some memory unsigned char* buffer = (unsigned char*) malloc (1024); // xor eax, eax // inc eax // inc eax // inc eax // ret -> eax should be 3 /* WORKS! buffer[0] = 0x67; buffer[1] = 0x31; buffer[2] = 0xC0; buffer[3] = 0x67; buffer[4] = 0x40; buffer[5] = 0x67; buffer[6] = 0x40; buffer[7] = 0x67; buffer[8] = 0x40; buffer[9] = 0xC3; */ // xor eax, eax // mov eax, 9 // ret 4 -> eax should be 9 /* WORKS! buffer[0] = 0x67; buffer[1] = 0x31; buffer[2] = 0xC0; buffer[3] = 0x67; buffer[4] = 0xB8; buffer[5] = 0x09; buffer[6] = 0x00; buffer[7] = 0x00; buffer[8] = 0x00; buffer[9] = 0xC3; */ // push ebp // mov ebp, esp // mov eax, [ebp + 6] ; wtf? shouldn't this be [ebp + 8]!? // mov esp, ebp // pop ebp // ret -> eax should be the first value sent to the function /* WORKS! */ buffer[0] = 0x66; buffer[1] = 0x55; buffer[2] = 0x66; buffer[3] = 0x89; buffer[4] = 0xE5; buffer[5] = 0x66; buffer[6] = 0x66; buffer[7] = 0x8B; buffer[8] = 0x45; buffer[9] = 0x06; buffer[10] = 0x66; buffer[11] = 0x89; buffer[12] = 0xEC; buffer[13] = 0x66; buffer[14] = 0x5D; buffer[15] = 0xC3; // mov eax, 5 // add eax, ecx // ret -> eax should be 50 /* WORKS! buffer[0] = 0x67; buffer[1] = 0xB8; buffer[2] = 0x05; buffer[3] = 0x00; buffer[4] = 0x00; buffer[5] = 0x00; buffer[6] = 0x66; buffer[7] = 0x01; buffer[8] = 0xC8; buffer[9] = 0xC3; */ return buffer; } And finally I have the main chunk of the program: void main (int argc, char **args) { DWORD oldProtect = (DWORD) NULL; int i = 667, j = 1, k = 5, l = 0; // generate some arbitrary function _JIT_METHOD someFunc = (_JIT_METHOD) compile(NULL); // windows only #if defined _WIN64 || defined _WIN32 // set memory permissions and flush CPU code cache VirtualProtect(someFunc,1024,PAGE_EXECUTE_READWRITE, &oldProtect); FlushInstructionCache(GetCurrentProcess(), someFunc, 1024); #endif // this asm just for some debugging/testing purposes __asm mov ecx, i // run compiled function (from wherever *someFunc is pointing to) l = (int)someFunc(i, k); // did it work? printf("result: %d", l); free (someFunc); _getch(); } As you can see, the compile() function has a couple of tests I ran to make sure I get expected results, and pretty much everything works but I have a question... On most tutorials or documentation resources, to get the first value of a function passed (in the case of ints) you do [ebp+8], the second [ebp+12] and so forth. For some reason, I have to do [ebp+6] then [ebp+10] and so forth. Could anyone tell me why?

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  • setcontext and makecontext to call a generic function pointer

    - by Simone Margaritelli
    In another question i had the problem to port the code unsigned long stack[] = { 1, 23, 33, 43 }; /* save all the registers and the stack pointer */ unsigned long esp; asm __volatile__ ( "pusha" ); asm __volatile__ ( "mov %%esp, %0" :"=m" (esp)); for( i = 0; i < sizeof(stack); i++ ){ unsigned long val = stack[i]; asm __volatile__ ( "push %0" :: "m"(val) ); } unsigned long ret = function_pointer(); /* restore registers and stack pointer */ asm __volatile__ ( "mov %0, %%esp" :: "m" (esp) ); asm __volatile__ ( "popa" ); To a 64bit platform and many guys told me i should use the setcontext and makecontext functions set instead due to the calling conversion differences between 32 and 64 bits and portability issues. Well, i really can't find any useful documentation online, or at least not the kind i need to implement this, so, how can i use those functions to push arguments onto the stack, call a generic function pointer, obtain the return value and then restore the registers?

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  • how do addressing modes work on a physical level?

    - by altvali
    I'm trying to learn this basic thing about processors that should be taught in every CS department of every university. Yet i can't find it on the net (Google doesn't help) and i can't find it in my class materials either. Do you know any good resource on how addressing modes work on a physical level? I'm particularly interested in Intel processors.

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  • Implementing a Mutex Lock in C

    - by Adam
    I'm trying to make a really mutex in C and for some reason I'm getting cases where two threads are getting the lock at the same time, which shouldn't be possible. Any ideas why it's not working? void mutexLock(mutex_t *mutexlock, pid_t owner) { int failure; while(mutexlock->mx_state == 0 || failure || mutexlock->mx_owner != owner) { failure = 1; if (mutexlock->mx_state == 0) { asm( "test:" "movl $0x01,%%eax\n\t" // move 1 to eax "xchg %%eax,%0\n\t" // try to set the lock bit "mov %%eax,%1\n\t" // export our result to a test var "test %%eax,%%eax\n\t" "jnz test\n\t" :"=r"(mutexlock->mx_state),"=r"(failure) :"r"(mutexlock->mx_state) :"%eax" ); } if (failure == 0) { mutexlock->mx_owner = owner; //test to see if we got the lock bit } } }

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  • ASM x86 relative JMP

    - by benlaug
    Hi, I'm doing some ASM code in a C code with the asm function. My environment is DVL with gcc version 3. Hi need to make a JMP to a relative address like %eip+0x1f. How can I do this ? Thanks

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  • WinForms app config manager is x86 and cannot reference assemblies that targets Any CPU

    - by ivos
    Hi I'm using Win7 64x and Visual Studio 2010. I created a library/framework targeting Any CPU. Then I created a new WinForms project that uses that framework, leaving the default values of the wizard. I mean, I didn't change anything. When I reference my framework, VS cannot find the assemblies. If I go to the project properties, it is targeting Any CPU (as expected, I can change it if I want). But if I go to Configuration Manager, the only choice I have for that project is x86. And I guess that is the problem. I tried to add Any CPU as a new Target but I was unable to. Could someone help me? :) Thanks in advance!

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  • What does subl do here?

    - by drozzy
    So... I'm compiling into assembler, with gcc -S -O2 -m32: void h(int y){int x; x=y+1; f(y); f(2); } And it gives me the following: .file "sample.c" .text .p2align 4,,15 .globl h .type h, @function h: pushl %ebp movl %esp, %ebp subl $24, %esp movl 8(%ebp), %eax movl %eax, (%esp) call f movl $2, 8(%ebp) leave jmp f .size h, .-h .ident "GCC: (GNU) 4.4.3 20100127 (Red Hat 4.4.3-4)" .section .note.GNU-stack,"",@progbits Now I know what pushl and movel: they store the current frame pointer onto the stack and then set the value of the frame pointer register to the value of the Stack Pointer. But I have no idea what the subl $24, %esp is. Thanks!

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  • Combining prefixes in SSE

    - by Nathan Fellman
    In SSE the prefixes 066h (operand size override) 0F2H (REPNE) and 0F3h (REPE) are part of the opcode. In non-SSE 066h switches between 32-bit (or 64-bit) and 16-bit operation. 0F2h and 0F3h are used for string operations. They can be combined so that 066h and 0F2h (or 0F3h) can be used in the same instruction, because this is meaningful. What is the behavior in an SSE instruction? For instance, we have (ignoring mod/rm for now): 0f 58 -- addps 66 0f 58 -- addpd f2 0f 58 -- addsd f3 0f 58 -- addss But what is this? 66 f2 0f 58 And how about? f2 66 0f 58 Not to mention the following which has two conflicting REP prefixes: f2 f3 0f 58 What is the spec for thse?

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  • Need some help deciphering a line of assembler code, from .NET JITted code

    - by Lasse V. Karlsen
    In a C# constructor, that ends up with a call to this(...), the actual call gets translated to this: 0000003d call dword ptr ds:[199B88E8h] What is the DS register contents here? I know it's the data-segment, but is this call through a VMT-table or similar? I doubt it though, since this(...) wouldn't be a call to a virtual method, just another constructor. I ask because the value at that location seems to be bad in some way, if I hit F11, trace into (Visual Studio 2008), on that call-instruction, the program crashes with an access violation. The code is deep inside a 3rd party control library, where, though I have the source code, I don't have the assemblies compiled with enough debug information that I can trace it through C# code, only through the disassembler, and then I have to match that back to the actual code. The C# code in question is this: public AxisRangeData(AxisRange range) : this(range, range.Axis) { } Reflector shows me this IL code: .maxstack 8 L_0000: ldarg.0 L_0001: ldarg.1 L_0002: ldarg.1 L_0003: callvirt instance class DevExpress.XtraCharts.AxisBase DevExpress.XtraCharts.AxisRange::get_Axis() L_0008: call instance void DevExpress.XtraCharts.Native.AxisRangeData::.ctor(class DevExpress.XtraCharts.ChartElement, class DevExpress.XtraCharts.AxisBase) L_000d: ret It's that last call there, to the other constructor of the same class, that fails. The debugger never surfaces inside the other method, it just crashes. The disassembly for the method after JITting is this: 00000000 push ebp 00000001 mov ebp,esp 00000003 sub esp,14h 00000006 mov dword ptr [ebp-4],ecx 00000009 mov dword ptr [ebp-8],edx 0000000c cmp dword ptr ds:[18890E24h],0 00000013 je 0000001A 00000015 call 61843511 0000001a mov eax,dword ptr [ebp-4] 0000001d mov dword ptr [ebp-0Ch],eax 00000020 mov eax,dword ptr [ebp-8] 00000023 mov dword ptr [ebp-10h],eax 00000026 mov ecx,dword ptr [ebp-8] 00000029 cmp dword ptr [ecx],ecx 0000002b call dword ptr ds:[1889D0DCh] // range.Axis 00000031 mov dword ptr [ebp-14h],eax 00000034 push dword ptr [ebp-14h] 00000037 mov edx,dword ptr [ebp-10h] 0000003a mov ecx,dword ptr [ebp-0Ch] 0000003d call dword ptr ds:[199B88E8h] // this(range, range.Axis)? 00000043 nop 00000044 mov esp,ebp 00000046 pop ebp 00000047 ret Basically what I'm asking is this: What the purpose of the ds:[ADDR] indirection here? VMT-table is only for virtual isn't it? and this is constructor Could the constructor have yet to be JITted, which could mean that the call would actually call through a JIT shim? I'm afraid I'm in deep water here, so anything might and could help. Edit: Well, the problem just got worse, or better, or whatever. We are developing the .NET feature in a C# project in a Visual Studio 2008 solution, and debugging and developing through Visual Studio. However, in the end, this code will be loaded into a .NET runtime hosted by a Win32 Delphi application. In order to facilitate easy experimentation of such features, we can also configure the Visual Studio project/solution/debugger to copy the produced dll's to the Delphi app's directory, and then execute the Delphi app, through the Visual Studio debugger. Turns out, the problem goes away if I run the program outside of the debugger, but during debugging, it crops up, every time. Not sure that helps, but since the code isn't slated for production release for another 6 months or so, then it takes some of the pressure off of it for the test release that we have soon. I'll dive into the memory parts later, but probably not until over the weekend, and post a followup.

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  • Modify EXE to stop launching firefox

    - by Random Joe
    I'm using a wireless modem program from my ISP. This program automatically disconnect when it detects the line is idle. It does so in 2-5 minutes of idle time. Whenever I reconnect, It will automatically fire up my default browser to the ISP portal. I DID NOT pay them to shove their web portal in my face 50 times a day. The ISP provides no options for disabling this behavior. Can someone please show me how to hex edit the EXE program to stop it from annoying the hell out of me?

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  • Using ret with FASM on Win32

    - by Jon Purdy
    I'm using SDL with FASM, and have code that's minimally like the following: format ELF extrn _SDL_Init extrn _SDL_SetVideoMode extrn _SDL_Quit extrn _exit SDL_INIT_VIDEO equ 0x00000020 section '.text' public _SDL_main _SDL_main: ccall _SDL_Init, SDL_INIT_VIDEO ccall _SDL_SetVideoMode, 640, 480, 32, 0 ccall _SDL_Quit ccall _exit, 0 ; Success, or ret ; failure. With the following quick-and-dirty makefile: SOURCES = main.asm OBJECTS = main.o TARGET = SDLASM.exe FASM = C:\fasm\fasm.exe release : $(OBJECTS) ld $(OBJECTS) -LC:/SDL/lib/ -lSDLmain -lSDL -LC:/MinGW/lib/ -lmingw32 -lcrtdll -o $(TARGET) --subsystem windows cleanrelease : del $(OBJECTS) %.o : %.asm $(FASM) $< $@ Using exit() (or Windows' ExitProcess()) seems to be the only way to get this program to exit cleanly, even though I feel like I should be able to use retn/retf. When I just ret without calling exit(), the application does not terminate and needs to be killed. Could anyone shed some light on this? It only happens when I make the call to SDL_SetVideoMode().

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  • ASP.NET reading files from BIN

    - by nettguy
    I am processing some CSV file which i have copied in Bin folder of My ASP.NET Website. When i execute using (IDataReader csv = new CsvReader (new StreamReader("sample.txt"), true, '|')) { ..... } it complains me that "sample.txt" not found in "c:\Program Files\.....\" Won't the runtime automatically look into the bin folder? what modification do i need to do?

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  • 80x86 16-bit asm: lea cx, [cx*8+cx] causes error on NASM (compiling .com file)

    - by larz
    Title says it all. The error NASM gives (dispite my working OS) is "invalid effective address". Now i've seen many examples of how to use LEA and i think i gots it right but yet my NASM dislikes it. I tried "lea cx, [cx+9]" and it worked; "lea cx, [bx+cx]" didn't. Now if i extended my registers to 32-bits (i.e. "lea ecx, [ecx*8+ecx]") everything would be well but i am restricted to use 16- and 8-bit registers only. Is here anyone so knoweledgeable who could explain me WHY my assembler doesn't let me use lea the way i supposed it should be used? Thanks.

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  • More about the Standard Entry Sequence

    - by Mask
    quoted from here: _function: push ebp ;store the old base pointer mov ebp, esp ;make the base pointer point to the current ;stack location – at the top of the stack is the ;old ebp, followed by the return address and then ;the parameters. sub esp, x ;x is the size, in bytes, of all ;"automatic variables" in the function What's stored in esp in the above code snippet?

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  • Why is a 16-bit register used with BSR instruction in this code snippet?

    - by sharptooth
    In this hardcore article there's a function find_maskwidth() that basically detects the number of bits required to represent itemCount dictinct values: unsigned int find_maskwidth( unsigned int itemCount ) { unsigned int maskWidth, count = itemCount; __asm { mov eax, count mov ecx, 0 mov maskWidth, ecx dec eax bsr cx, ax jz next inc cx mov maskWidth, ecx next: } return maskWidth; } the question is why do they use ax and cx registers instead of eax and ecx?

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