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  • Windows disassembler: looking for a tool...

    - by SigTerm
    Hello. I'm looking for a (preferably free) tool that can produce "proper" disassembly listing from a (non-.NET) windows PE file (*.exe or *.dll). Important requirement: it should be possible to run the listing through a windows assembler (nasm, masm or whatever) and get working exe again (not necessarily identical to original one, but it should behave in the same way). Intended usage is adding new subroutines into existing code, when source is not available. Ideally, tool should be able to detect function/segment boundaries, API calls, and generate proper labels for jumps (I can live without labels for loops/jumps, though, but function boundary detection would be nice), and keep program resources/segments in place. I'm already aware of IdaPRO(not free), OllyDBG (useful for in-place hacking, doesn't generate disassembly listing, AFAIK), ndisasm (output isn't suitable for assembler), dumpbin (useful, but AFAIK, output isn't suitable for assembler) and "proxy dll" technique. Ideas? Or maybe there is a book/tutorial that explains some kind of alternative approach?

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  • Why Aren't Programs Written In Assembly More Often?

    - by mudge
    It seems to be a mainstream opinion that assembly programming takes longer and is more difficult to program in than a higher level language such as C. Therefore it seems to be recommend or assumed that it is better to write in a higher level language for these reasons and for the reason of better portability. Recently I've been writing in x86 assembly and it has dawned on me that perhaps these reasons are not really true, except perhaps portability. Perhaps it is more of a matter of familiarity and knowing how to write assembly well. I also noticed that programming in assembly is quite different than programming in an HLL. Perhaps a good and experienced assembly programmer could write programs just as easily and as quickly as an experienced C programmer writing in C. Perhaps it is because assembly programming is quite different than HLLs, and so requires different thinking, methods and ways, which makes it seem very awkward to program in for the unfamiliar, and so gives it its bad name for writing programs in. If portability isn't an issue, then really, what would C have over a good assembler such as NASM?

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  • How to: Inline assembler in C++ (under Visual Studio 2010)

    - by toxic shock
    I'm writing a performance-critical, number-crunching C++ project where 70% of the time is used by the 200 line core module. I'd like to optimize the core using inline assembly, but I'm completely new to this. I do, however, know some x86 assembly languages including the one used by GCC and NASM. All I know: I have to put the assembler instructions in _asm{} where I want them to be. Problem: I have no clue where to start. What is in which register at the moment my inline assembly comes into play?

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  • How to access C arrays from assembler for Windows x64?

    - by 0xdword32
    I've written an assembler function to speed up a few things for image processing (images are created with CreateDIBSection). For Win32 the assembler code works without problems, but for Win64 I get a crash as soon as I try to access my array data. I put the relevant info in a struct and my assembler function gets a pointer to this struct. The struct pointer is put into ebx/rbx and with indexing I read the data from the struct. Any idea what I am doing wrong? I use nasm together with Visual Studio 2008 and for Win64 I set "default rel". C++ code: struct myData { tUInt32 ulParam1; void* pData; }; CallMyAssemblerFunction(&myData); Assembler Code: Win32: ... push ebp; mov ebp,esp mov ebx, [ebp + 8]; pointer to our struct mov eax, [ebx]; ulParam1 mov esi, [ebx + 4]; pData, 4 byte pointer movd xmm0, [esi]; ... Win64: ... mov rbx, rcx; pointer to our struct mov eax, [rbx]; ulParam1 mov rsi, [rbx + 4]; pData, 8 byte pointer movd xmm0, [rsi]; CRASH! ...

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  • How can I have a Makefile automatically rebuild source files that include a modified header file? (I

    - by Nicholas Flynt
    I have the following makefile that I use to build a program (a kernel, actually) that I'm working on. Its from scratch and I'm learning about the process, so its not perfect, but I think its powerful enough at this point for my level of experience writing makefiles. AS = nasm CC = gcc LD = ld TARGET = core BUILD = build SOURCES = source INCLUDE = include ASM = assembly VPATH = $(SOURCES) CFLAGS = -Wall -O -fstrength-reduce -fomit-frame-pointer -finline-functions \ -nostdinc -fno-builtin -I $(INCLUDE) ASFLAGS = -f elf #CFILES = core.c consoleio.c system.c CFILES = $(foreach dir,$(SOURCES),$(notdir $(wildcard $(dir)/*.c))) SFILES = assembly/start.asm SOBJS = $(SFILES:.asm=.o) COBJS = $(CFILES:.c=.o) OBJS = $(SOBJS) $(COBJS) build : $(TARGET).img $(TARGET).img : $(TARGET).elf c:/python26/python.exe concat.py stage1 stage2 pad.bin core.elf floppy.img $(TARGET).elf : $(OBJS) $(LD) -T link.ld -o $@ $^ $(SOBJS) : $(SFILES) $(AS) $(ASFLAGS) $< -o $@ %.o: %.c @echo Compiling $<... $(CC) $(CFLAGS) -c -o $@ $< #Clean Script - Should clear out all .o files everywhere and all that. clean: -del *.img -del *.o -del assembly\*.o -del core.elf My main issue with this makefile is that when I modify a header file that one or more C files include, the C files aren't rebuilt. I can fix this quite easily by having all of my header files be dependencies for all of my C files, but that would effectively cause a complete rebuild of the project any time I changed/added a header file, which would not be very graceful. What I want is for only the C files that include the header file I change to be rebuilt, and for the entire project to be linked again. I can do the linking by causing all header files to be dependencies of the target, but I cannot figure out how to make the C files be invalidated when their included header files are newer. I've heard that GCC has some commands to make this possible (so the makefile can somehow figure out which files need to be rebuilt) but I can't for the life of me find an actual implementation example to look at. Can someone post a solution that will enable this behavior in a makefile? EDIT: I should clarify, I'm familiar with the concept of putting the individual targets in and having each target.o require the header files. That requires me to be editing the makefile every time I include a header file somewhere, which is a bit of a pain. I'm looking for a solution that can derive the header file dependencies on its own, which I'm fairly certain I've seen in other projects.

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  • Help in building an 16 bit os

    - by Barshan Das
    I am trying to build an old 16 bit dos like os. My bootloader code: ; This is not my code. May be of Fritzos. I forgot the source. ORG 7c00h jmp Start drive db 0 msg db " Loader Initialization",0 msg2 db "ACos Loaded",0 print: lodsb cmp al, 0 je end mov ah, 0Eh int 10h jmp print end: ret Start: mov [ drive ], dl ; Get the floppy OS booted from ; Update the segment registers xor ax, ax ; XOR ax mov ds, ax ; Mov AX into DS mov si,msg call print ; Load Kernel. ResetFloppy: mov ax, 0x00 ; Select Floppy Reset BIOS Function mov dl, [ drive ] ; Select the floppy ADos booted from int 13h ; Reset the floppy drive jc ResetFloppy ; If there was a error, try again. ReadFloppy: mov bx, 0x9000 ; Load kernel at 9000h. mov ah, 0x02 ; Load disk data to ES:BX mov al, 17 ; Load two floppy head full's worth of data. mov ch, 0 ; First Cylinder mov cl, 2 ; Start at the 2nd Sector to load the Kernel mov dh, 0 ; Use first floppy head mov dl, [ drive ] ; Load from the drive kernel booted from. int 13h ; Read the floppy disk. jc ReadFloppy ; Error, try again. ; Clear text mode screen mov ax, 3 int 10h ;print starting message mov si,msg2 call print mov ax, 0x0 mov ss, ax mov sp, 0xFFFF jmp 9000h ; This part makes sure the bootsector is 512 bytes. times 510-($-$$) db 0 ;bootable sector signature dw 0xAA55 My example kernel code: asm(".code16\n"); void putchar(char); int main() { putchar('A'); return 0; } void putchar(char val) { asm("movb %0, %%al\n" "movb $0x0E, %%ah\n" "int $0x10\n" : :"r"(val) ) ; } This is how I compile it : nasm -f bin -o ./bin/boot.bin ./source/boot.asm gcc -nostdinc -fno-builtin -I./include -c -o ./bin/kernel.o ./source/kernel.c ld -Ttext=0x9000 -o ./bin/kernel.bin ./bin/kernel.o -e 0x0 dd if=/dev/zero of=./bin/empty.bin bs=1440K count=1 cat ./bin/boot.bin ./bin/kernel.bin ./bin/empty.bin|head -c 1440K > ./bin/os rm ./bin/empty.bin and I run it in virtual machine. When I make the putchar function ( in kernel code ) for constant value ....i.e like this: void putchar() { char val = 'A'; asm("movb %0, %%al\n" "movb $0x0E, %%ah\n" "int $0x10\n" : :"r"(val) ) ; } then it works fine. But when I pass argument to it ( That is in the previous code ) , then it prints a space for any character. What should I do?

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  • undefined reference to function, despite giving reference in c

    - by Jamie Edwards
    I'm following a tutorial, but when it comes to compiling and linking the code I get the following error: /tmp/cc8gRrVZ.o: In function `main': main.c:(.text+0xa): undefined reference to `monitor_clear' main.c:(.text+0x16): undefined reference to `monitor_write' collect2: ld returned 1 exit status make: *** [obj/main.o] Error 1 What that is telling me is that I haven't defined both 'monitor_clear' and 'monitor_write'. But I have, in both the header and source files. They are as follows: monitor.c: // monitor.c -- Defines functions for writing to the monitor. // heavily based on Bran's kernel development tutorials, // but rewritten for JamesM's kernel tutorials. #include "monitor.h" // The VGA framebuffer starts at 0xB8000. u16int *video_memory = (u16int *)0xB8000; // Stores the cursor position. u8int cursor_x = 0; u8int cursor_y = 0; // Updates the hardware cursor. static void move_cursor() { // The screen is 80 characters wide... u16int cursorLocation = cursor_y * 80 + cursor_x; outb(0x3D4, 14); // Tell the VGA board we are setting the high cursor byte. outb(0x3D5, cursorLocation >> 8); // Send the high cursor byte. outb(0x3D4, 15); // Tell the VGA board we are setting the low cursor byte. outb(0x3D5, cursorLocation); // Send the low cursor byte. } // Scrolls the text on the screen up by one line. static void scroll() { // Get a space character with the default colour attributes. u8int attributeByte = (0 /*black*/ << 4) | (15 /*white*/ & 0x0F); u16int blank = 0x20 /* space */ | (attributeByte << 8); // Row 25 is the end, this means we need to scroll up if(cursor_y >= 25) { // Move the current text chunk that makes up the screen // back in the buffer by a line int i; for (i = 0*80; i < 24*80; i++) { video_memory[i] = video_memory[i+80]; } // The last line should now be blank. Do this by writing // 80 spaces to it. for (i = 24*80; i < 25*80; i++) { video_memory[i] = blank; } // The cursor should now be on the last line. cursor_y = 24; } } // Writes a single character out to the screen. void monitor_put(char c) { // The background colour is black (0), the foreground is white (15). u8int backColour = 0; u8int foreColour = 15; // The attribute byte is made up of two nibbles - the lower being the // foreground colour, and the upper the background colour. u8int attributeByte = (backColour << 4) | (foreColour & 0x0F); // The attribute byte is the top 8 bits of the word we have to send to the // VGA board. u16int attribute = attributeByte << 8; u16int *location; // Handle a backspace, by moving the cursor back one space if (c == 0x08 && cursor_x) { cursor_x--; } // Handle a tab by increasing the cursor's X, but only to a point // where it is divisible by 8. else if (c == 0x09) { cursor_x = (cursor_x+8) & ~(8-1); } // Handle carriage return else if (c == '\r') { cursor_x = 0; } // Handle newline by moving cursor back to left and increasing the row else if (c == '\n') { cursor_x = 0; cursor_y++; } // Handle any other printable character. else if(c >= ' ') { location = video_memory + (cursor_y*80 + cursor_x); *location = c | attribute; cursor_x++; } // Check if we need to insert a new line because we have reached the end // of the screen. if (cursor_x >= 80) { cursor_x = 0; cursor_y ++; } // Scroll the screen if needed. scroll(); // Move the hardware cursor. move_cursor(); } // Clears the screen, by copying lots of spaces to the framebuffer. void monitor_clear() { // Make an attribute byte for the default colours u8int attributeByte = (0 /*black*/ << 4) | (15 /*white*/ & 0x0F); u16int blank = 0x20 /* space */ | (attributeByte << 8); int i; for (i = 0; i < 80*25; i++) { video_memory[i] = blank; } // Move the hardware cursor back to the start. cursor_x = 0; cursor_y = 0; move_cursor(); } // Outputs a null-terminated ASCII string to the monitor. void monitor_write(char *c) { int i = 0; while (c[i]) { monitor_put(c[i++]); } } void monitor_write_hex(u32int n) { s32int tmp; monitor_write("0x"); char noZeroes = 1; int i; for (i = 28; i > 0; i -= 4) { tmp = (n >> i) & 0xF; if (tmp == 0 && noZeroes != 0) { continue; } if (tmp >= 0xA) { noZeroes = 0; monitor_put (tmp-0xA+'a' ); } else { noZeroes = 0; monitor_put( tmp+'0' ); } } tmp = n & 0xF; if (tmp >= 0xA) { monitor_put (tmp-0xA+'a'); } else { monitor_put (tmp+'0'); } } void monitor_write_dec(u32int n) { if (n == 0) { monitor_put('0'); return; } s32int acc = n; char c[32]; int i = 0; while (acc > 0) { c[i] = '0' + acc%10; acc /= 10; i++; } c[i] = 0; char c2[32]; c2[i--] = 0; int j = 0; while(i >= 0) { c2[i--] = c[j++]; } monitor_write(c2); } monitor.h: // monitor.h -- Defines the interface for monitor.h // From JamesM's kernel development tutorials. #ifndef MONITOR_H #define MONITOR_H #include "common.h" // Write a single character out to the screen. void monitor_put(char c); // Clear the screen to all black. void monitor_clear(); // Output a null-terminated ASCII string to the monitor. void monitor_write(char *c); #endif // MONITOR_H common.c: // common.c -- Defines some global functions. // From JamesM's kernel development tutorials. #include "common.h" // Write a byte out to the specified port. void outb ( u16int port, u8int value ) { asm volatile ( "outb %1, %0" : : "dN" ( port ), "a" ( value ) ); } u8int inb ( u16int port ) { u8int ret; asm volatile ( "inb %1, %0" : "=a" ( ret ) : "dN" ( port ) ); return ret; } u16int inw ( u16int port ) { u16int ret; asm volatile ( "inw %1, %0" : "=a" ( ret ) : "dN" ( port ) ); return ret; } // Copy len bytes from src to dest. void memcpy(u8int *dest, const u8int *src, u32int len) { const u8int *sp = ( const u8int * ) src; u8int *dp = ( u8int * ) dest; for ( ; len != 0; len-- ) *dp++ =*sp++; } // Write len copies of val into dest. void memset(u8int *dest, u8int val, u32int len) { u8int *temp = ( u8int * ) dest; for ( ; len != 0; len-- ) *temp++ = val; } // Compare two strings. Should return -1 if // str1 < str2, 0 if they are equal or 1 otherwise. int strcmp(char *str1, char *str2) { int i = 0; int failed = 0; while ( str1[i] != '\0' && str2[i] != '\0' ) { if ( str1[i] != str2[i] ) { failed = 1; break; } i++; } // Why did the loop exit? if ( ( str1[i] == '\0' && str2[i] != '\0' || (str1[i] != '\0' && str2[i] =='\0' ) ) failed =1; return failed; } // Copy the NULL-terminated string src into dest, and // return dest. char *strcpy(char *dest, const char *src) { do { *dest++ = *src++; } while ( *src != 0 ); } // Concatenate the NULL-terminated string src onto // the end of dest, and return dest. char *strcat(char *dest, const char *src) { while ( *dest != 0 ) { *dest = *dest++; } do { *dest++ = *src++; } while ( *src != 0 ); return dest; } common.h: // common.h -- Defines typedefs and some global functions. // From JamesM's kernel development tutorials. #ifndef COMMON_H #define COMMON_H // Some nice typedefs, to standardise sizes across platforms. // These typedefs are written for 32-bit x86. typedef unsigned int u32int; typedef int s32int; typedef unsigned short u16int; typedef short s16int; typedef unsigned char u8int; typedef char s8int; void outb ( u16int port, u8int value ); u8int inb ( u16int port ); u16int inw ( u16int port ); #endif //COMMON_H main.c: // main.c -- Defines the C-code kernel entry point, calls initialisation routines. // Made for JamesM's tutorials <www.jamesmolloy.co.uk> #include "monitor.h" int main(struct multiboot *mboot_ptr) { monitor_clear(); monitor_write ( "hello, world!" ); return 0; } here is my makefile: C_SOURCES= main.c monitor.c common.c S_SOURCES= boot.s C_OBJECTS=$(patsubst %.c, obj/%.o, $(C_SOURCES)) S_OBJECTS=$(patsubst %.s, obj/%.o, $(S_SOURCES)) CFLAGS=-nostdlib -nostdinc -fno-builtin -fno-stack-protector -m32 -Iheaders LDFLAGS=-Tlink.ld -melf_i386 --oformat=elf32-i386 ASFLAGS=-felf all: kern/kernel .PHONY: clean clean: -rm -f kern/kernel kern/kernel: $(S_OBJECTS) $(C_OBJECTS) ld $(LDFLAGS) -o $@ $^ $(C_OBJECTS): obj/%.o : %.c gcc $(CFLAGS) $< -o $@ vpath %.c source $(S_OBJECTS): obj/%.o : %.s nasm $(ASFLAGS) $< -o $@ vpath %.s asem Hopefully this will help you understand what is going wrong and how to fix it :L Thanks in advance. Jamie.

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