Re: Defining a section that isn't file-backed

[Nick Clifton <nickc at redhat dot com>]

Hi Mike,

> I'd like to use a linker script to define an ELF section that isn't
> backed by disk space in the resulting binary, that I can place at a
> specific absolute address in memory.
>
> By "not backed" I mean something a bit like the BSS where the
> section could be (say) 256mb but only take up a few bytes on
> disk. If the resulting section is assigned to a read-only VMA range,
> then I think the result should be equivalent to a MAP_NORESERVE |
> MAP_FIXED mmap before the dynamic linker runs - am I correct?

Not sure about that, sorry.

> If this is possible, what sort of script would I be looking for?
> Alternatively which part of the ld manual describes how to do it, as
> I've looked and not been able to find any info on this.

What you need is a combination of a linker script and an assembler
source file.  For example if you create an assembler file containing
this:
	.section .empty, "a", @nobits
	.zero 40000

and then a linker script which contains:

        .empty 0x100 : { KEEP (*(.empty)) }

You should get what you want.  Obviously you will need to change the
numbers to reflect the size and location that you want.

Cheers
        Nick