c,assembly,operating-system,kernel,hex , C Kernel - Works fine on VM but not actual computer?


C Kernel - Works fine on VM but not actual computer?

Question:

Tag: c,assembly,operating-system,kernel,hex

I am making a basic C kernel. (Loaded by an assembly program) I am compiling it with an i686-elf cross compiler for windows. My C code is as follows:

void cls();
void drawhappy();
void main(){
    char *vidptr = (char *)0xb8000;
    cls();
    drawhappy();
}

void cls(){
    char *vidptr = (char *)0xb8000;
    unsigned int j = 0;
    while(j < 80*2*25){
        vidptr[j] = ' ';
        vidptr[j+1] = 0x07;
        j = j+2;
    }
}

void drawhappy(){
    char *vidptr = (char *)0xb8000;
    const unsigned int linewidth = 80*2;
    vidptr[3] = 0xa7;
    vidptr[5] = 0xa7;
    vidptr[7] = 0xa7;
    vidptr[9] = 0xa7;
    vidptr[1+linewidth] = 0xa7;
    vidptr[5+linewidth] = 0xa7;
    vidptr[7+linewidth] = 0xa7;
    vidptr[11+linewidth] = 0xa7;
    vidptr[1+linewidth*2] = 0xa7;
    vidptr[3+linewidth*2] = 0xa7;
    vidptr[5+linewidth*2] = 0xa7;
    vidptr[7+linewidth*2] = 0xa7;
    vidptr[9+linewidth*2] = 0xa7;
    vidptr[11+linewidth*2] = 0xa7;
    vidptr[1+linewidth*3] = 0xa7;
    vidptr[5+linewidth*3] = 0xa7;
    vidptr[7+linewidth*3] = 0xa7;
    vidptr[11+linewidth*3] = 0xa7;
    vidptr[1+linewidth*4] = 0xa7;
    vidptr[11+linewidth*4] = 0xa7;
    vidptr[3+linewidth*5] = 0xa7;
    vidptr[5+linewidth*5] = 0xa7;
    vidptr[7+linewidth*5] = 0xa7;
    vidptr[9+linewidth*5] = 0xa7;
}

In bochs, it gives me the expected output: Yay And if I use bootice to write the bin file to the boot sector and run it as a VM on virtualbox, it works too. But if I actually boot from the USB stick, It just kinda goes crazy then puts a weird symbol by the bottom right corner of my screen. (No screenshot because I obviously can't) I have an i7-3770K CPU. Why is this happening?

EDIT: Here's my assembly code:

[org 0x7c00]
KERNEL_OFFSET equ 0x1000

    mov [BOOT_DRIVE], dl

    mov bp, 0x9000
    mov sp, bp

    mov bx, MSG_REAL_MODE
    call print_string

    call load_kernel

    call switch_to_pm

jmp $

%include "C:/Users/Aaron/Desktop/CODE_OS/print_string.asm"
; load DH sectors to ES:BX from drive DL
disk_load:
    push dx

    mov ah, 0x02
    mov al, dh
    mov ch, 0x00
    mov dh, 0x00
    mov cl, 0x02

    int 0x13

    jc disk_error

    pop dx
    cmp dh, al
    jne disk_error
    ret

disk_error:
    mov bx, DISK_ERROR_MSG
    call print_string
    jmp $

DISK_ERROR_MSG: db "Disk read error!", 0
%include "C:/Users/Aaron/Desktop/CODE_OS/print_string_pm.asm"
%include "C:/Users/Aaron/Desktop/CODE_OS/switch_to_pm.asm"
; GDT
gdt_start:

gdt_null:   ; the mandatory null descriptor
    dd 0x0
    dd 0x0

gdt_code:   ; the code segment descriptor
    dw 0xffff   ; limit
    dw 0x0      ; base
    db 0x0
    db 10011010b
    db 11001111b
    db 0x0

gdt_data:
    dw 0xffff
    dw 0x0
    db 0x0
    db 10010010b
    db 11001111b
    db 0x0

gdt_end:

gdt_descriptor:
    dw gdt_end - gdt_start - 1
    dd gdt_start

CODE_SEG equ gdt_code - gdt_start
DATA_SEG equ gdt_data - gdt_start

[bits 16]

load_kernel:
    mov bx, MSG_LOAD_KERNEL
    call print_string

    mov bx, KERNEL_OFFSET
    mov dh, 15
    mov dl, [BOOT_DRIVE]
    call disk_load

    ret

[bits 32]

BEGIN_PM:
    mov ebx, MSG_PROT_MODE
    call print_string_pm

    call KERNEL_OFFSET

    jmp $

BOOT_DRIVE db 0
MSG_REAL_MODE  db 'Started in 16-bit Real Mode',0
MSG_PROT_MODE db 'Successfully booted to 32-bit Protected Mode',0
MSG_LOAD_KERNEL db "Loading Kernel...",0

times 510-($-$$) db 0 ; Pad the boot sector out with zeros
dw 0xaa55 ; Last two bytes form the magic number

(Print-string.asm just prints strings, switch_to_pm.asm switches to protected mode, and print_string_pm.asm prints strings in protected mode.)


Answer:

You're not initializing the segment registers. Try changing the start of your bootsector to something like this:

xor ax, ax
mov bp, 0x9000
mov ds, ax
mov es, ax
mov ss, ax ; disables interrupts until the end of the next instruction
mov sp, bp
mov [BOOT_DRIVE], dl

Related:


What does `strcpy(x+1, SEQX)` do?


c,strcpy
I'm wondering what this syntax of strcpy() does in line 65 and 66: 24 #define SEQX "TTCATA" 25 #define SEQY "TGCTCGTA" 61 M = strlen(SEQX); 62 N = strlen(SEQY); 63 x = malloc(sizeof(char) * (M+2)); /* +2: leading blank, and trailing \0 */ 64 y = malloc(sizeof(char) * (N+2)); 65...

Disadvantages of calling realloc in a loop


c,memory-management,out-of-memory,realloc
I'm trying to implement some math algorithms in C on Windows 7, and I need to repeatedly increase size of my array. Sometimes it fails because realloc can't allocate memory. But if I allocate a lot of memory at once in the beginning it works fine. Is it a problem...

Program to reverse a string in C without declaring a char[]


c,string,pointers,char
I need to reverse a given string and display it without using the value At[index] notation , I tried the below program using pointers,but it does not print anything for the reverse string, Please help! int main() { char* name=malloc(256); printf("\nEnter string\n"); scanf("%s",name); printf("\nYou entered%s",name); int i,count; count=0; //find the...

C++ / C #define macro calculation


c++,c,macros
Suppose I have #define DETUNE1 sqrt(7)-sqrt(5) #define DETUNE2 sqrt(11)-sqrt(7) And I call these multiple times in my program. Are DETUNE1 and DETUNE2 calculated every time it is called? Thanks. Please don't downvote this, I really want to know and a search didn't turn up anything definite. ...

How to control C Macro Precedence


c,macros
#define VAL1CHK 20 #define NUM 1 #define JOIN(A,B,C) A##B##C int x = JOIN(VAL,NUM,CHK); With above code my expectation was int x = 20; But i get compilation error as macro expands to int x = VALNUMCHK; // Which is undefined How to make it so that NUM is replaced first...

Is it safe to read and write on an array of 32 bit data byte by byte?


c,memory,memory-alignment
So I have a void * data of 32 bit unsigned integers which represents the pixels. Is it okay for me to access one of the pixels with a char * and modify the values directly? Or is it better to store my new pixel in a temporary uint32_t variable...

How can I align stack to the end of SRAM?


c,embedded,stm32,gnu-arm,coocox
I have a STM32F103VCT6 microcontroller with 48kb of SRAM, and recently i've got a memory collision: I have some static variable (lets call it A) located in heap with size of 0x7000 and I wrote some simple function to get info about stack and heap: void check(int depth) { char...

execl() works on one of my code, but doesn't work on another


c,execl
I already used execl() in code, and it worked well. But this time, I really have no idea why it doesn't work. So here's the code that do not work #include <unistd.h> #include <stdio.h> int main() { int i = 896; printf("please\n"); execl("home/ubuntu/server/LC/admin/admin", (char*)i, NULL); printf("i have no idea why\n");...

How convert unsigned int to unsigned char array


c++,c
I just need to extract those bytes using bitwise & operator. 0xFF is a hexadecimal mask to extract one byte. For 2 bytes, this code is working correctly: #include <stdio.h> int main() { unsigned int i = 0x7ee; unsigned char c[2]; c[0] = i & 0xFF; c[1] = (i>>8) &...

Does realloc() invalidate all pointers?


c,pointers,dynamic-memory-allocation,behavior,realloc
Note, this question is not asking if realloc() invalidates pointers within the original block, but if it invalidates all the other pointers. I'm new to C, and am a bit confused about the nature of realloc(), specifically if it moves any other memory. For example: void* ptr1 = malloc(2); void*...

Unexpected result when calculating a percentage - even when factoring in integer division rules


c,percentage,integer-overflow,integer-division
I am trying to express a battery voltage as a percentage. My battery level is a (global) uint16 in mV. I have a 16-bit CPU. Here is my code: static uint8 convertBattery(void){ uint16 const fullBattery = 3000; /* 3V = 3000mV */ uint8 charge; charge = ((battery*100)/fullBattery); return charge; }...

On entry to NIT parameter number 9 had an illegal value


c,mpi,intel-mkl,mpich,scalapack
I go this ex1.c file from Intel 11. However, when I execute it, it fails: [email protected]:~/konstantis$ ../mpich-install/bin/mpicc -o test ex1.c -I../intel/mkl/include ../intel/mkl/lib/intel64/libmkl_scalapack_ilp64.a -Wl,--start-group ../intel/mkl/lib/intel64/libmkl_intel_ilp64.a ../intel/mkl/lib/intel64/libmkl_core.a ../intel/mkl/lib/intel64/libmkl_sequential.a -Wl,--end-group ../intel/mkl/lib/intel64/libmkl_blacs_intelmpi_ilp64.a -lpthread -lm -ldl [email protected]:~/konstantis$ mpiexec -n 4 ./test { 0, 0}: On entry to DESCI{...

Multiple definition and file management


c,arrays,compilation,compiler-errors,include
I'm writing a program for vocabulary training, for myself. And the program itself should be available in different languages, atm in German and English. What I want is to have a Main File which manage all and two separate files for the functions in the right language. I compile all...

Infinite loop with fread


c,arrays,loops,malloc,fread
I'm trying to allocate an array 64 bytes in size and then loop over the array indexes to put a read a byte each from the inputfile. but when I don't malloc() the array indexes, the loop stays in index0 (so each time it loops it replaces the content in...

Efficient comparison of small integer vectors


c,integer,compare,bit-manipulation,string-comparison
I have small vectors. Each of them is made of 10 integers which are between 0 and 15. This means that every element in a vector can be written using 4 bits. Hence I can concatenate my vector elements and store the whole vector in a single long type (in...

How does ((a++,b)) work? [duplicate]


c,function,recursion,comma
This question already has an answer here: What does the comma operator `,` do in C? 8 answers In the below block of code, I am trying to understand how the line return reverse((i++, i)) is working. #include <stdio.h> void reverse(int i); int main() { reverse(1); } void reverse(int...

Reverse ^ operator for decryption


c,algorithm,security,math,encryption
I'm trying to reverse the following code in order to provide a function which takes the buffer and decrypts it. void crypt_buffer(unsigned char *buffer, size_t size, char *key) { size_t i; int j; j = 0; for(i = 0; i < size; i++) { if(j >= KEY_SIZE) j = 0;...

Passing int using char pointer in C


c,exec,ipc
I'm trying to figure out how to pass an int using a char pointer. It fails once the int value is too large for the char. This is what I'm trying to figure out: char *args[5]; int i = 20; /*some other code/assignments*/ args[2] = (char *)&i; execv(path, args); How...

Segmentation Fault if I don't say int i=0


c,arrays,segmentation-fault,initialization,int
void removeVowels(char* array){ int i,j,v; i=0; char vowel[]={'a','e','i','o','u'}; while(array[i]!='\0') { for(v=0;v<5;v++) { if (array[i]==vowel[v]) { j=i; while(array[j]!='\0') { array[j]=array[j+1]; j++; } i--; break; } } i++; } } in function removeVowels() if I don't include i=0; and just say int i; why does it give segmentation fault? Isn't it automatically...

Galois LFSR - how to specify the output bit number


c,prng,shift-register
I am trying to understand how change the galois LFSR code to be able to specify the output bit number as a parameter for the function mentioned below. I mean I need to return not the last bit of LFSR as output bit, but any bit of the LFSR (...

free causing different results from malloc


c,string,malloc,free
Below is a C program i have written to print different combination of characters in a string. This is not an efficient way as this algorithm creats a lot of extra strings. However my question is NOT about how to solve this problem more efficiently. The program works(inefficiently though) and...

Is there any way of protecting a variable for being modified at runtime in C?


c,variables,constants
I was wondering if there is any way of protecting a variable for being modified once initialized (something like "constantize" a variable at runtime ). For example: #include <stdio.h> #include <stdlib.h> int main(void) { int v, op; scanf( "%d", &op ); if( op == 0 ) v = 1; else...

How to read string until two consecutive spaces?


c,format,sscanf,c-strings
A well known function of the scanf() functions is that you can pass a format to scan input according to this format. For my case, I cannot seem to find a solution searching this and this documentation. I have a string (sInput) as the following: #something VAR1 this is a...

Counter not working after jumps - assembly language


loops,assembly,counter,increment
For some reason, when i switch to mouse input switch back to keyboard input for my program, increasing and decreasing the counter has no effect. It works perfectly in the first loop where we input characters. Here is the program guys, any advice? look at whatspeed jump for reference after...

Is i=i+1 an undefined behaviour?


c,increment,undefined-behavior
I'm using codeblocks and it is giving a different output to other compilers and I can't find a solution to it.What's the undefined behaviour in this program and is there any solution to avoid it? This is the code to print the nth number in a number system with only...

Is post-increment operator guaranteed to run instantly?


c,c89,post-increment,ansi-c
Let's say I have the following code: int i = 0; func(i++, i++); The increment is happening right after returning the value? Is it guaranteed that the first argument will be 0, and the second argument will be 1?...

How does this code print odd and even?


c,if-statement,macros,logic
#define MACRO(num, str) {\ printf("%d", num);\ printf(" is");\ printf(" %s number", str);\ printf("\n");\ } int main(void) { int num; printf("Enter a number: "); scanf("%d", &num); if (num & 1) { MACRO(num, "Odd"); } else { MACRO(num, "Even"); } return 0; } Please explain the above code (if/else condition and how...

Text justification C language


c,text,alignment
I have to solve a problem that involves left justification string length and leading zeros. I have the following table : BEGIN CLOSE CONCATENATE DELETE END INITIALIZE PRINT WRITE This is produced by a simple program. My problem is to find out how to convert it like that : It...

VS2012 Identifer not found when part of static lib


c,visual-studio-2012,linker,static-libraries
Using VS2012 C/C++: I created and linked a static lib called "libtools" to my project. Calls to functions in the libtools lib worked as expected. I created and linked a second static lib called "shunt" to my project. But when I incorporate a call to a function in shunt, I...

Recursive signal call using kill function


c,signals
I'm now learning signals in computer system and I've stuck with a problem. There is a code given below; int i = 0; void handler(int s) { if(!i) kill(getpid(), SIGINT); i++; } int main() { signal(SIGINT, handler); kill(getpid(), SIGINT); printf("%d\n", i); return 0; } And the solution says that the...

Counting bytes received by posix read()


c,function,serial-port,posix
I get confused with one line of code: temp_uart_count = read(VCOM, temp_uart_data, 4096); I found more about read function at http://linux.die.net/man/3/read, but if everything is okay it returns 0, so how we can get num of bytes received from that? temp_uart_count is used to count how much bytes we received...

C language, vector of struct, miss something?


c,vector,struct
This is a part of my program that I want to create a vector of struct typedef struct { char nome[501]; int qtd; int linha; int coluna; } tPeca; tPeca* criarPecas(FILE *pFile, int tam) { int i; tPeca *pecaJogo = (tPeca*)malloc(tam*sizeof(tPeca)); if (pecaJogo == NULL) return NULL; for (i =...

Segmentation fault with generating an RSA and saving in ASN.1/DER?


c,openssl,cryptography,rsa
#include <string.h> #include <openssl/aes.h> #include <openssl/rand.h> #include <openssl/bio.h> #include <openssl/rsa.h> #include <openssl/evp.h> #include <openssl/pem.h> #define RSA_LEN 2048 #define RSA_FACTOR 65537 int genRSA2048(unsigned char **pub,unsigned int *pub_l,unsigned char **priv,unsigned int *priv_l){ RSA *pRSA = NULL; pRSA = RSA_generate_key(RSA_LEN,RSA_FACTOR,NULL,NULL); if (pRSA){ pub_l = malloc(sizeof(pub_l)); *pub_l = i2d_RSAPublicKey(pRSA,pub); priv_l = malloc(sizeof(priv_l));...

How to increment the value of an unsigned char * (C)


c++,c,openssl,byte,sha1
I have a value stored as an unsigned char * (in C). This holds the SHA1 hash of a string. My goal is to cover the SHA1 key space. Since I'm using <openssl/evp.h> to generate the hashes, I end up with an unsigned char* holding the SHA1 value. Now I...

C binary tree sort - extending it


c,binary-tree,binary-search-tree
I need some help in C Help me to extend the binary tree sort on C. I need to return a sorted array in sort function. here it is: #include <stdio.h> #include <stdlib.h> struct btreenode { struct btreenode *leftchild ; int data ; struct btreenode *rightchild ; } ; void...

OpenGL glTexImage2D memory issue


c,opengl
I'm loading a cubemap to create a skybox, everything is fine and the skybox renders properly with a correct texture application. However, I decided to check my program safety with valgrind, Valgrind gives this error: http://pastebin.com/seqmXjyx The line 53 in sky.c is: glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X + i, 0, GL_RGB, texture.width, texture.height, 0,...

scanf get multiple values at once


c,char,segmentation-fault,user-input,scanf
I need to get in one single shot different inputs from one single line. In particular I need to get a single char and then, depending on which char value I just read, it can be a string and an int or a string, an int and another string and...

CGO converting Xlib XEvent struct to byte array?


c,go,xlib,cgo
I am creating a simple window manager (code based of the c code in tinywm) in Golang. To use Xlib, I am using cgo, so my header is: // #cgo LDFLAGS: -lX11 // #include <X11/Xlib.h> And I have a variable declaration, like: event := C.XEvent{} And then, I use this...

getchar() not working in c


c,while-loop,char,scanf,getchar
getchar() is not working in the below program, can anyone help me to solve this out. I tried scanf() function in place of getchar() then also it is not working. I am not able to figure out the root cause of the issue, can anyone please help me. #include<stdio.h> int...

Does strlen() always correctly report the number of char's in a pointer initialized string?


c,strlen
As long as I use the char and not some wchar_t type to declare a string will strlen() correctly report the number of chars in the string or are there some very specific cases I need to be aware of? Here is an example: char *something = "Report all my...

CallXXXMethod undefined using JNI in C


java,c,jni
So I've tried to use the JNI interface to call Java methods from C. Calling static methods is no problem, but I get stuck when I want to call a method on an object. The code is as follows: #include <stdio.h> #include <string.h> #include <jni.h> int main() { JavaVMOption options[1];...

Loop through database table and compare user input


mysql,c
I am trying to loop through the rows in a MySql table and compare the data in a certain column to some user input using C. Currently my code looks like this: MYSQL *cxn = mysql_init(NULL); MYSQL_RES *result; unsigned int num_fields; unsigned int num_rows; char *query_string; MYSQL_ROW *row; if (mysql_real_connect(cxn,...

Is there Predefined-Macros define about byte order in armcc


c,armcc,predefined-macro
Is there Predefined-Macros define about byte order in armcc. I am a novice on the armcc.and sorry for my English. In gcc these are macros: __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__ __ORDER_BIG_ENDIAN__ __ORDER_PDP_ENDIAN__ ... Now I have to use armcc, Is there same like these with armcc? Thank a lot. by the way,the armcc...

Array breaking in Pebble C


c,arrays,pebble-watch,cloudpebble
I'm trying to create a simple dice-rolling application in Pebble using C on CloudPebble. I have an array of different die sizes you can scroll through using Up/Down, and you roll (currently just generate a random number, it'll get fancier later) using the middle button. There's also a label at...

ARM assembly cannot use immediate values and ADDS/ADCS together


gcc,assembly,arm,instructions
I am currently trying to speed up some of my C functions on a Cortex-M0 (Freescale KL25Z) using assembly. I get a problem with this minimal test program: @.syntax unified .cpu cortex-m0 .text .global test .code 16 test: mov r0, #0 adds r0, r0, #1 bx lr When I try...

NASM: copying a pointer from a register to a buffer in .data


linux,assembly,nasm,x86-64
I am new to asm. I am trying to copy a pointer from a register to a .data variable using NASM, on linux 64-bit. Concider this program: section .data ptr: dq 0 section .text global _start _start: mov [ptr], rsp mov rax, 60 mov rdi, 0 syscall Here I try...

Set precision dynamically using sprintf


c,printf,format-string
Using sprintf and the general syntax "%A.B" I can do this: double a = 0.0000005l; char myNumber[50]; sprintf(myNumber,"%.2lf",a); Can I set A and B dynamically in the format string?...

What all local variables goto Data/BSS segment?


c++,c,nm
The man page of nm here: MAN NM says that The symbol type. At least the following types are used; others are, as well, depending on the object file format. If lowercase, the symbol is usually local; if uppercase, the symbol is global (external) And underneath it has "b" and...

fread(), solaris to unix portability and use of uninitialised values


c,linux,memory,stack,portability
Valgrind found the following error and I, after reading the documentation, the code and other questions in here couldn't figure it out why. Valgrind: first warning ~$ valgrind --vgdb=yes --vgdb-error=0 --read-var-info=yes --leak-check=yes --track-origins=yes debitadmin* debitadmin ==20720== Conditional jump or move depends on uninitialised value(s) ==20720== at 0x4013BC6: initialise (dbg.c:199) ==20720==...

C programming - Confusion regarding curly braces


c,scope
The following code is for replacing multiple consecutive spaces into 1 space. Although I manage to do it, I am confused in the use of curly braces. This one is actually running fine: #include <stdio.h> #include <stdlib.h> int main() { int ch, lastch; lastch = 'a'; while((ch = getchar())!= EOF)...