OSDev.org

Posted: **Wed Jan 30, 2013 1:03 pm**

hello! I again ask for help...
I was transforming my kernel from 32bit to 64 but when I modified my ld script and the assembly entry of the kernel appeared this problem: the linker puts 1MB of zeros between the elf header and the multiboot header and the entry and also between the entry and the kernel (that for the moment I simplified to an empty c++ function) making the binary 2,2MB large and making grub not detecting the multiboot header. To find the problem I left only the multiboot header and a loop in my assembly entry file and only the boot section in the ld script but the problem persists.

my simplified entry is this

Code: Select all

[BITS 32]

extern _loadStart
extern _loadEnd
extern _bssEnd


;XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
;	MULTIBOOT HEADER
;XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
section .multibootheader

ALIGN 8
Mb1Hdr:
	;MULTIBOOT 1
	
magic		dd	0x1badb002
flags		dd	0x2
checksum	dd	-0x1badb002-0x2
	
Mb1HdrEnd:


;XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
;	CODICE
;XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

section .boot


global loader
loader:
	xchg	bx,bx

hang:
    	hlt
    	jmp  hang

and the ld script is this

Code: Select all

ENTRY (loader)
OUTPUT_FORMAT(elf64-x86-64)
OUTPUT(kernel.bin)

SECTIONS
{
	. = 0x100000;
	.boot :
	{
		*(.multibootheader )
		_loadStart = . ;
		*(.boot)	
	}
	_loadEnd = .;
	_bssEnd = .;

}

readelf says this about the file created

Code: Select all

readelf -S kernel.bin
There are 5 section headers, starting at offset 0x100038:

Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 0]                   NULL             0000000000000000  00000000
       0000000000000000  0000000000000000           0     0     0
  [ 1] .boot             PROGBITS         0000000000100000  00100000
       0000000000000012  0000000000000000   A       0     0     8
  [ 2] .shstrtab         STRTAB           0000000000000000  00100012
       0000000000000021  0000000000000000           0     0     1
  [ 3] .symtab           SYMTAB           0000000000000000  00100178
       0000000000000150  0000000000000018           4    10     8
  [ 4] .strtab           STRTAB           0000000000000000  001002c8
       0000000000000062  0000000000000000           0     0     1
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings), l (large)
  I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown)
  O (extra OS processing required) o (OS specific), p (processor specific)

I'm using nasm for assembling (using the command: "nasm -f elf64 -o sorgenti/OSentry.o sorgenti/OSentry.s") and I link using the command: "x86_64-elf-ld -T linker.ld -o kernel.bin sorgenti/OSentry.o".

thank you in advance if you know what I'm doing wrong or what's causing this.

Posted: **Wed Jan 30, 2013 1:23 pm**

OSDev Wiki

Posted: **Wed Jan 30, 2013 2:55 pm**

ah. ops, I didnt saw that. thank you.
The "-z max-page-size=0x1000" option solved the problem

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problem with linking, 1MB of zeros at binary beginning

problem with linking, 1MB of zeros at binary beginning

Re: problem with linking, 1MB of zeros at binary beginning

Re: problem with linking, 1MB of zeros at binary beginning