Initialised data after end of kernel that shouldn't be there

[jrhetf4xb]

Hi,

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

Code: Select all

    ...

    .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?

[Candy]

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

[jrhetf4xb]

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 = .;
}

[eryjus]

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).

[jrhetf4xb]

Alright, thanks both!