Re: Using bfd to change the .text section of an executable

[Alan Modra <amodra at gmail dot com>]

On Wed, Mar 23, 2011 at 02:29:40PM -0600, Eric Schulte wrote:
> However, any changes which change the size of the .text section (in this
> case appending four noops to the end) the resulting file is no longer a
> working executable but rather throws segfaults on execution.

Not surprising.  I suspect you seriously underestimate how much work
is required to change section VMAs in a final linked executable, and
have it run afterwards.

> After some investigation it appears that while bfd is updating the lma
> address of all sections following the .text section in memory (as shown
> in the bfd warnings printed in [1] when running my `copy' program, the
> source code for which is included below in [2]) bfd is not making
> similar adjustments to the vma field of these sections.
> 
> Is it possible to convince bfd to manage vma addresses for me?

Nope.

>  I've
> tried setting the `user_set_vma' flag to 0 before making the copy, but
> to no avail.  Also, attempts to set the vma field of these sections
> manually before calling bfd_close don't have any effect on the resulting
> output file.

See objcopy --change-section-vma code.

-- 
Alan Modra
Australia Development Lab, IBM