OSDev.org

My GCC Flags wrote:CCFLAGS=-O3 -Wall -Wextra -pedantic -Wshadow -Wpointer-arith -Wcast-align -Wwrite-strings \
-Wmissing-prototypes -Wmissing-declarations -Wredundant-decls -Wnested-externs -Winline \
-Wno-long-long -Wuninitialized -Wconversion -Wstrict-prototypes -Wunsafe-loop-optimizations \
-std=gnu99 -nostdinc -fno-builtin -fno-stack-protector -march=i686 -m32 -I $(INCLUDES)

BASICFreak wrote:[Opinion] I consider it bad practice myself to preset variables, I rather an init function. Or if constant enum or #define them. [/Opinion]

BASICFreak wrote:Simply put, RTFM - Learn the tools you are using (eg. What does GCC and LD do, What flags should I consider, what do the flags do, etc.)

I can assume you are using a standard GCC install and not a cross-compiler (which is fine, if you know GCCs flags - I don't use a cross compiler)

First, At the very least, at least tell the compiler not to use standard libraries and to warn you on everything (just because something is not an error does not mean it is not an ERROR - especially in OSDev).

My GCC Flags wrote:CCFLAGS=-O3 -Wall -Wextra -pedantic -Wshadow -Wpointer-arith -Wcast-align -Wwrite-strings \
-Wmissing-prototypes -Wmissing-declarations -Wredundant-decls -Wnested-externs -Winline \
-Wno-long-long -Wuninitialized -Wconversion -Wstrict-prototypes -Wunsafe-loop-optimizations \
-std=gnu99 -nostdinc -fno-builtin -fno-stack-protector -march=i686 -m32 -I $(INCLUDES)

Second, Get a makefile - it makes the job so much easier, and will only compile the modified files.

Third, A linker script is also nice, you need more than the Text section most the time, plus why are you going to binary from elf-i386?
* If you want binary you should (IMHO) use aout not elf.

Forth, the program I think you are looking for is AR, which can make a "library" (actually an archive) of your object files, but you will not have to worry about this with a proper makefile.

And as for the global variable; it is probably set correctly, just in the wrong location (or not in the file since we only have .Text no Data nor BSS)
[Opinion] I consider it bad practice myself to preset variables, I rather an init function. Or if constant enum or #define them. [/Opinion]

Hopefully this points you towards the right direction.

BASICFreak wrote:I can assume you are using a standard GCC install and not a cross-compiler (which is fine, if you know GCCs flags - I don't use a cross compiler)

Octocontrabass wrote:

BASICFreak wrote:I can assume you are using a standard GCC install and not a cross-compiler (which is fine, if you know GCCs flags - I don't use a cross compiler)

You should be using a cross-compiler. If nothing else, you need the freestanding libgcc. This is not optional: all code compiled with GCC must be linked against libgcc.

RezaNoei wrote:i tested that by objdump -d foo.o

Octocontrabass wrote:

RezaNoei wrote:i tested that by objdump -d foo.o

Try using objdump -h foo.o instead. Do you see any sections with names like .data?

                                                 
#include "../Include/string.h"
#include "../Include/stdio.h"

#define CellCount 80*25
uint8_t CurrentX=0;
uint8_t CurrentY=0;

uint8_t Color = 14;
uint8_t *VideoMemory = (uint8_t *)0xb8000;

void initial()
{
  Color = 0 ;
  VideoMemory = (uint16_t*)0xb8000;
}
void putch(const char ch)
{
//      initial();
        uint8_t *VID = VideoMemory;
        *(VID++) = 'D';
        *(VID++) = Color;
}
void clrscr(void)
{
        size_t i;
        for (i=0;i<CellCount*2;i++)
        {
            if (i%2)
            {
                   VideoMemory[i] = Color;
                   Color = (Color+1)%16;
             }
        }
}
void gotoxy(uint8_t X,uint8_t Y){}

 file format elf32-i386

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .text         0000011f  00000000  00000000  00000034  2**0
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
  1 .data         00000000  00000000  00000000  00000153  2**0
                  CONTENTS, ALLOC, LOAD, DATA
  2 .bss          00000002  00000000  00000000  00000153  2**0
                  ALLOC
  3 .comment      00000012  00000000  00000000  00000153  2**0
                  CONTENTS, READONLY
  4 .eh_frame     000000d8  00000000  00000000  00000168  2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA

iansjack wrote:So, isn't your variable there in the .bss section?

objdump  -t stdio.o

file format elf32-i386

SYMBOL TABLE:
00000000 l    df *ABS*	00000000 stdio.c
00000000 l    d  .text	00000000 .text
00000000 l    d  .data	00000000 .data
00000000 l    d  .bss	00000000 .bss
00000000 l    d  .eh_frame	00000000 .eh_frame
00000000 l    d  .comment	00000000 .comment
00000000 g     O .bss	00000001 CurrentX
00000001 g     O .bss	00000001 CurrentY
00000001       O *COM*	00000001 Color
00000004       O *COM*	00000004 VideoMemory
00000000 g     F .text	00000005 puts
00000005 g     F .text	00000016 initial
0000001b g     F .text	00000092 putch
000000ad g     F .text	00000018 printf
000000c5 g     F .text	00000046 clrscr
0000010b g     F .text	00000014 gotoxy

uint8_t * VideoMem = (uint8_t *)0xb8000;
void putc(char ch)
{
*(VideoMem++) = ch;
*(VideMem++) = 14;
}

Combuster wrote:I only see 2 of the expected 7 bytes (3 uint8s and one pointer) in the .bss

What are your compile instructions and linker script?

all:
        nasm -f elf Loader.asm -o Loader.o
        i386-elf-gcc -ffreestanding -c SysCore/Kernel/kernel.c -o Kernel.o -m32
        i386-elf-ld -o Shams.bin -Ttext 0x7c00 -Tdata 0x7f00 Loader.o Kernel.o SysCore/Lib/Debug/stdio.o  --oformat binary -m elf_i386

all:
        i386-elf-gcc -c -ffreestanding stdio.c -o Debug/stdio.o -m32

00000000 g     O .bss	00000001 CurrentX
00000001 g     O .bss	00000001 CurrentY
00000002 g     O .bss	00000001 Color
00000004 g     O .bss	00000004 VideoMemory

Octocontrabass wrote:

BASICFreak wrote:I can assume you are using a standard GCC install and not a cross-compiler (which is fine, if you know GCCs flags - I don't use a cross compiler)

You should be using a cross-compiler. If nothing else, you need the freestanding libgcc. This is not optional: all code compiled with GCC must be linked against libgcc.

kiznit wrote:

BASICFreak wrote:[Opinion] I consider it bad practice myself to preset variables, I rather an init function. Or if constant enum or #define them. [/Opinion]

Ugh?? Care to elaborate?

BASICFreak wrote:In the world of OSDev I have ran across many random issues I have never seen is userland code for *nix/Win. A lot of the time it is one of the sections of the linked file not being where the rest of the program expects. If you set the variables in the code, it will set the variable where the code THINKS it SHOULD be.