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Posted: **Tue Mar 30, 2010 9:05 am**

Hi all, this is my first post here ^^

I'm starting to develop my kernel, but I get those

start.o:(.text+0x2d): undefined reference to `_kmain'

As I'm quite new on compiling on linux I think I did something wrong while ./configure or so...
On the wiki there is a tutorial on how compiling gcc an binutils, but nothing for nasm (or at least i couldn find it...)
This is what I did:

I downloaded the nasm source code, untared it and cd into it's folder, then

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export PREFIX=/usr/cross
export TARGET=i586-elf
./configure --prefix=$PREFIX --target=$TARGET
make all
make install

export PATH=$PATH:$PREFIX/bin
$TARGET-nasm -f elf -o start.o start.asm

It says: i586-elf-nasm: no se encontró la orden (which means that couldn't find the order)
If I assembly it using

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nasm -f elf -o start.o start.asm

I get the _kmain error while linking... yagh

Thanks in advance

Posted: **Tue Mar 30, 2010 9:25 am**

Obviously, "_kmain" and "kmain" are not the same thing... Fix your spelling

Posted: **Tue Mar 30, 2010 9:44 am**

... It fixed it, however in the wiki says:

I get unresolved references to kmain, or others because of missing / superfluous underscores in the object files !?
As an immediate resolve, you can use -fno-leading-underscores or -fleading-underscores to get the object file variant you need; in the long run, you might want to set up a GCC Cross-Compiler with the correct default behavior.

I want to do it the good way, not the fast one...

Thanks for the fast reply

Posted: **Tue Mar 30, 2010 9:53 am**

As quoted, if you have the GCC Cross-Compiler built according to those instructions, it has the correct behaviour by default. Which means there are no leading underscores.

Note that the default depends on the host you are compiling for - on DOS and Windows leading underscores are customary, while on practically all others they are not. Which is one of the reasons why you should use a cross-compiler: to get rid of the host platform-specific features the compiler throws into your OS.

Posted: **Tue Mar 30, 2010 12:04 pm**

mmm....still having trouble.
I couldnt find anything on the forums nor wiki.

If I try to call a function made in asm i get an undefined reference error while linking. And this time is not a spelling error.

The assembly code:

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global gdt_flush
extern gp
gdt_flush:
    lgdt [gp]
    mov ax, 0x10
    mov ds, ax
    mov es, ax
    mov fs, ax
    mov gs, ax
    mov ss, ax
    jmp 0x08:flush2
flush2:
    ret

and the C code:

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struct gdt_entry gdt[3];
struct gdt_ptr gp;

extern void gdt_flush(void);

void gdt_install(void)
{
    /* Setup the GDT pointer and limit */
    gp.limit = (sizeof(struct gdt_entry) * 3) - 1;
    gp.base = (int)&gdt;

    gdt_set_gate(0, 0, 0, 0, 0);
    gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
    gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
    gdt_flush();
}

Then I just assembly, compile everything, and then link it:

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nasm -f elf -o start.o start.asm
$TARGET-gcc -Wall -Wextra -Werror -O -fstrength-reduce -fomit-frame-pointer -finline-functions -nostdinc -fno-builtin -fno-leading-underscore -I./include -c -o gdt.o gdt.c
$TARGET-ld -T link.ld -o kernel.bin start.o kernel.o gdt.o display.o

I've really no clue why it fails, I even tried adding '_' everywhere xD

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gdt.o: In function `gdt_install':
gdt.c:(.text+0xb2): undefined reference to `gdt_flush'

Thanks

Posted: **Tue Mar 30, 2010 12:22 pm**

did you use sections?

Posted: **Tue Mar 30, 2010 12:32 pm**

Only the .bss for the stack... Do I have to define all of them?
However I think I'm going to start again following another tutorial.

Posted: **Tue Mar 30, 2010 12:38 pm**

My .ld looks like this:

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OUTPUT_FORMAT("binary")
ENTRY(start)
SECTIONS
{
  .text 0x100000 :
  {
    code = .; _code = .; __code = .;
    *(.text)
    . = ALIGN(4096);
  }

  .data :
  {
     data = .; _data = .; __data = .;
     *(.data)
     *(.rodata)
     . = ALIGN(4096);
  }

  .bss :
  {
    bss = .; _bss = .; __bss = .;
    *(.bss)
    . = ALIGN(4096);
  }

  end = .; _end = .; __end = .;
}

And I think in the assembly everything is .text except the part that says:

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SECTION .bss
    resb 8192               ; This reserves 8KBytes of memory here
sys_stack:

And thats the last thing I have on my assembly file. I feel like a big noob xD
I dont really know too much about assembly, apart from microcontroler's asm.

Posted: **Tue Mar 30, 2010 12:52 pm**

nake wrote:I think

Don't think, know. Especially when you have already proven yourself wrong somewhere

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