how to tell ld not to pad the file?

[Luis]

Hi,

I want to set different virtual memory addresses for different sections as you can see in the example code but as I do that the file gets padded with 0s between addresses. I've been trying to find a solution from barebones tutorial, linker script wiki, this forum and ld manual but I can't.

ld does: vaddress1 - 0x7C00, file_offset1: 0x7C00, vaddress2: 0x80000, file_offset2: 0x80000
I want: vaddress1 - 0x7C00, file_offset1: header_size, vaddress2: 0x80000, file_offset2: header_size+section1_size

There has to be a way to force ld to have different virtual addresses and file offsets.

Note: loader.o is assembled from fasm with a couple of org directives.

Code: Select all

start = 0x7C00;
ENTRY (start)
OUTPUT_FORMAT (elf64-x86-64)

SECTIONS
{
	.loader (0x7C00) : {
		*(.flat)
	}
	
	. = 0x80000;
	.kernel : {
		*(.text)
		*(.eh_frame)
	}
}

Cheers,
Luís

[Owen]

Sure there is. Read the Binutils manpages.

Hint: AT(x).

[Luis]

Sorry I still have no clue about what I am missing.

[Nable]

Sorry I still have no clue about what I am missing.

Hm, here's the chain of links that brought me to the description of above-mentioned attribute "AT()":
http://wiki.osdev.org/Linker_Scripts -> first foot-note (http://sourceware.org/binutils/docs-2.21/ld/index.html) -> http://sourceware.org/binutils/docs-2.2 ... ml#Scripts -> http://sourceware.org/binutils/docs-2.2 ... l#SECTIONS -> http://sourceware.org/binutils/docs-2.2 ... Attributes -> http://sourceware.org/binutils/docs-2.2 ... ection-LMA

[Luis]

Thanks!!! I guess I must be blind. I've been at that page and missed the AT. It works only if I change output format to binary. Elf format with AT still makes big files. Anyway that's ok bebause I don't really use elf to load kernel, I just use it sometimes to be able to objdump and see the sections as objdump doesn't work with binary format.

[xenos]

You might also need a linker option such as -z max-page-size=0x1000 when linking your ELF kernel - see also here.

[sortie]

Don't combine your bootloader and the actual x86_64 kernel into the same binary.

[Luis]

Don't combine your bootloader and the actual x86_64 kernel into the same binary.

Too late already done. Is there a good reason why I shouldn't? It's working fine as it is.