inline-assembly

I am trying to build an old 16 bit DOS like OS. 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

I am writing a tiny OS as part of an assigment for school,but I got stuck when it comes to get keyboard input (press a key -> display it on screen). I am using the Bare Bones tutorial from osdev.org (gcc cross-compiler, GRUB bootloader, ld linker) and since I am in protected mode I can not use BIOS interrupts for input, that's why I have to write my own interrupt handler (?) but I'm not sure how to do that even after I read some osdev articles and forum discussions. Very similar problem ( http://forum.osdev.org/viewtopic.php?f=1&t=9746 ) except that I don't know how to "set up the interrupts".

I am trying to create an ldm (resp. stm ) instruction with inline assembly but have problems to express the operands (especially: their order). A trivial void *ptr; unsigned int a; unsigned int b; __asm__("ldm %0!,{%1,%2}" : "+&r"(ptr), "=r"(a), "=r"(b)); does not work because it might put a into r1 and b into r0 : ldm ip!, {r1, r0} ldm expects registers in ascending order (as they are encoded in a bitfield) so I need a way to say that the register used for a is lower than this of b . A trivial way is the fixed assignment of registers: register unsigned int a asm("r0"); register unsigned int b

I have some trouble with some inline assembly code. I know what should be done but I miss the "how" ! I have this checksum function that is "almost" working : static unsigned long cksum_unroll( unsigned short **w, int *mlen) { int len; unsigned short *w0; unsigned long sum=0; len = *mlen; w0 = *w; while( len >= 8) { asm volatile ( "ldmia %[w0]!, {v1, v2}\n\t" "adds %[sum], %[sum], v1\n\t" "adcs %[sum], %[sum], v2\n\t" "adcs %[sum], %[sum], #0" : [sum] "+r" (sum) : [w0] "r" (w0) ); len -= 8; } *mlen = len; *w = w0; return (sum); } My problem, I believe, is on the line " : [sum] "+r" (sum) : [w0

I'm writing code to temporarily use my own stack for experimentation. This worked when I used literal inline assembly. I was hardcoding the variable locations as offsets off of ebp. However, I wanted my code to work without haivng to hard code memory addresses into it, so I've been looking into GCC's EXTENDED INLINE ASSEMBLY. What I have is the following: volatile intptr_t new_stack_ptr = (intptr_t) MY_STACK_POINTER; volatile intptr_t old_stack_ptr = 0; asm __volatile__("movl %%esp, %0\n\t" "movl %1, %%esp" : "=r"(old_stack_ptr) /* output */ : "r"(new_stack_ptr) /* input */ ); The point of

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

i use devcpp and borland c compiler.... asm { mov ax,4 // (I/O Func.) mov bx,1 // (Output func) mov cx,&name // (address of the string) mov dx,6 // (length of the string) int 0x21 // system call } in the above code snippets i want to print a string with the help of assembly language... but how can i put the address of the string in register cx.... is there something wrong in code??? I don't have the Borland compiler on hand, so I might be misremembering its syntax, but have you tried this: asm { mov ax,4 // (I/O Func.) mov bx,1 // (Output func) lds cx,"Hello, world" // (address of the string)