Controlling File Offset in linking

I have some assembler for the Microblaze that I want to load at address 0x00000000 (ie to ensure it is executed on a reset).

I have a linker script that should do this (I think):

SECTIONS
{
    ENTRY(_start)
    . = 0x0000;
    .vectors.reset : { *(.vectors.reset) }
    . = 0x0008;
    .vectors.sw_exception : { *(.vectors.sw_exception) }
    . = 0x0010;
    .vectors.interrupt : { *(.vectors.interrupt) }
    . = 0x0018;
    .vectors.hw_exception : { *(.vectors.hw_exception) }
    . = 0x100;
    .text : { *(.text) }
    .data : { *(.data) }
    .bss : { *(.bss) }
}

But when the code is compiled it seems to be offset by 0x1000:

objdump -h startup.MICROBLAZE.elf 

startup.MICROBLAZE.elf:     file format elf32-big

Sections:
Idx Name          Size      VMA       LMA       File off  Algn  
  0 .vectors.reset 00000008  00000000  00000000  00001000  2**2
                   CONTENTS, ALLOC, LOAD, READONLY, CODE
  1 .vectors.sw_exception 00000008  00000008  00000008  00001008  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
  2 .vectors.interrupt 00000008  00000010  00000010  00001010  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
  3 .vectors.hw_exception 00000008  00000018  00000018  00001018  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
  4 .text         00000020  00000100  00000100  00001100  2**4
                  CONTENTS, ALLOC, LOAD, READONLY, CODE

Where does that offset come from and how can I supress/control it?

Edit: It seems the 0x1000 offset is the physical offset of the code section in the compiled file/object - is that correct?

According to your objdump listing everything is suppose to be laid out as you expect. I.e. VMA and LMA of your .text section are pointing to address 0x100.

The offset 0x1000 as you correctly guessed is offset of the .text section inside ELF file. But this section will be loaded to address 0x100.

If you try to disassemble your ELF with

$ objdump -S startup.MICROBLAZE.elf

you will see the proper instructions layout. It is also helpful to produce MAP file on a linkage stage with -Wl,-Map,output.map gcc flags.