Re: RFC: Improve support for "debugging" unlinked objects

[Michael Snyder <msnyder at redhat dot com>]

Daniel Jacobowitz wrote:
> If you compile a file containing both code and initialized data, and load
> the unlinked object (.o) file using GDB, "print Variable" won't work. 
> You'll get garbage-looking data, which is in fact the start of the first
> section in the file - usually .text.
>
> All sections appear to have address 0.  i.e., they overlap, sort of like
> overlays but not similar enough to reuse the overlay machinery.  For this
> case, if we fill in section_offsets, we can place them at random locations
> which are sufficiently unique that we can see the locations of variables as
> distinct.  And if we pass this information back to exec.c, we can see the
> values of variables correctly, too.
>
> Here's a patch along with a testcase; the test fails before the patch, and
> passes afterwards.  Any comments on the way I fixed this?

I think this is a great idea, and...

> Also, with a fix that I'm going to commit to bfd soon, you
> can use "gdb -write" to patch an object file.

this bit's especially great.

One suggestion -- could you use the section's file offset
in place of a "random location"?  I'm guessing it's available
from bfd, and it seems to me that it's guaranteed to be unique.

There might be some advantage in terms of following non-relocated
branches etc.

Michael