OSDev.org

Posted: **Mon Mar 09, 2015 10:06 am**

Hi,

In my kernel linker script I have a symbol to easily point to the last address used by the kernel:

    ...

    .bss ALIGN (0x1000) :
    {
        sbss = .;
        *(COMMON)
        *(.bss)
        *(.gnu.linkonce.b*)
        ebss = .;
    }

    kernel_end = .;
}

When my kernel runs this turns out to be address 0x00302074. However, upon examining the memory after this location, about 4KiB later there is some data that I have no idea where it comes from. I'm really confused why there is data after the kernel so I was wondering if anyone had any ideas what that could be.

This is some data around 4KiB after the address:

Note I'm using qemu, so unitialised addresses read 0 instead of garbage data. Could it be data from qemu or GRUB's multiboot data? All I'm doing in the kernel is loading a GDT with statically defined structs and utilising a simple kprintf() function. All the static data is supposedly located before kernel_end, no?

Posted: **Mon Mar 09, 2015 1:43 pm**

Does your linker script that you're not entirely showing have a discard section? If not, that's what's there.

Posted: **Mon Mar 09, 2015 1:52 pm**

There isn't any, this is the full script:

Code: Select all

ENTRY (loader)

SECTIONS
{
    . = 0x00100000;

    kernel_start = .;

    .text ALIGN (0x1000) :
    {
        *(.text*)
        *(.gnu.linkonce.t*)
    }

    .rodata ALIGN (0x1000) :
    {
        start_ctors = .;
        *(.ctor*)
        end_ctors = .;

        start_dtors = .;
        *(.dtor*)
        end_dtors = .;

        *(.rodata*)
        *(.gnu.linkonce.r*)
    }

    .data ALIGN (0x1000) :
    {
        *(.data)
        *(.gnu.linkonce.d*)
    }

    .bss ALIGN (0x1000) :
    {
        sbss = .;
        *(COMMON)
        *(.bss)
        *(.gnu.linkonce.b*)
        ebss = .;
    }

    kernel_end = .;
}

Posted: **Mon Mar 09, 2015 7:29 pm**

Since you are not discarding any sections, you are probably looking at your symbol table and shared string table (not to be confused with the static strings in your code).

Posted: **Tue Mar 10, 2015 9:59 am**

Alright, thanks both!

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