[Dwarf-Discuss] security implications of DWARF info

David Anderson davea42@earthlink.net
Wed Nov 24 22:56:55 GMT 2010

On 11/24/2010 07:34 AM, James Oakley wrote:
> You and I disagree about security through obscurity, but this list is 
> not the place for that discussion.
> > However, I'm not familiar with libraries for
> > writing/generating/modifying DWARF files.  I checked the FAQ today;
> > the entries are empty.
> libdwarf (http://reality.sgiweb.org/davea/dwarf.html) is a library for 
> reading and modifying DWARF information. There's outdated 
> documentation for the consumer part of the library at 
> ftp://ftp.software.ibm.com/software/os390/czos/dwarf/libdwarf2.1.pdf. 
> There's a pdf with some documentation about the producer part of the 
> library somewhere as well, but I can't find the link at the moment. 
> There may be better/more current documentation.

The latest libdwarf/dwarfdump source distribution always has the latest 
doc, in .mm and .pdf forms.

Libdwarf is not a library like typical  DOM xml access libraries.  DOM 
access typically allows
reading xml into a tree in memory and modifying the tree in-situ and 
writing it back out.

Libdwarf was conceived (in ~1991) as a tool for compiler-writers and 
debuggers (as separate tasks).   So the consumer
and producer code are totally separate headers and functions (but 
packaged in
one archive or shared-library).   It is not easy to unify the  
consumer/producer tasks
as libdwarf is written.   There is the beginnings of a read/write tool 
(dwarfgen) in recent libdwarf releases,
but it is just a beginning, a hint.

The only other read/write tool using libdwarf  that I recall seeing is 
dwarfextract.  It's
intended to gather the type data from numerous kernel  .o files and 
condense it into a single .o
with no type duplications  (Written by Cliff Wickman when we were both 
at SGI, open sourced
by SGI in 2005).
A version of dwarfextract is in the testsuite release (on same dwarf.h 
web page, but separate
from libdwarf/dwarfdump).

David Anderson

Thank God men cannot as yet fly and lay waste the sky as well as the earth!  -- Henry David Thoreau

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