Removing specific symbols from debug section

[tex]

Hello,

can this library be used to create an application that would remove debug information of some specific symbols from existing elf binary?

Thanks!

[davea42]

The simple answer is 'NO'.

DWARF is as compact as possible (depending on compiler-writer
choices) and that makes changing content challenging: Essentially reading it all in to a set of graphs
removing parts, and writing a new object file. Just removing stuff, or just setting blobs of bytes to zeros
will destroy the DWARF involved. The library cannot store or rewrite such graphs ( such was never part of its design).

One thing is doable though. In strings in the .debug_str section zeroing
out bytes will not destroy the DWARF, it will still be readable.

Altering non-null ASCII bytes in any string anywhere in DWARF to be any non-null
ASCII character (possibly the dot (.)) will not destroy the DWARF.

For strings in the .debug_info section ( or .debug_line or others) zeroing out any bytes have
a very very high probability of destroying/corrupting the DWARF, making it unreadable.

[tex]

Thank you! I also found that zeroing out the first byte of string representing symbols in .debug_str section I do not want debugger to show appears to work.

[davea42]

I wrote "One thing is doable though. In strings in the .debug_str section zeroing
out bytes will not destroy the DWARF, it will still be readable". To avoid destroying
and UTF8 multi-byte code points I should have said:

"In strings in the .debug_str section zeroing
out ASCII bytes will not destroy the DWARF, it will still be readable"

Zeroing out portions of a utf8 codepoint is probably safe, though of course
attempts to print the string may fail somehow. If dwarfdump encounters
a damaged UTF8 codepoint when printing a name dwarfdump treats
the entire string as if it was not UTF8 and prints non-ascii bytes
in a uri-style %nn. There is a nice source out there that detects
invalid UTF8 quickly: http://bjoern.hoehrmann.de/utf-8/decoder/dfa/
and that is embedded in src/bin/dwarfdump/dd_utf8.c

[tex]

Thanks. We want only remove our symbols which we know are ASCII.