2009-08-31 Status

[Petr Machata <pmachata at redhat dot com>]

Last week
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Time spent on elfutils: 70%

Work on output.
     * Drop DWARF4 bits that I've had in before for experimenting (e.g. 
DW_FORM_flag_present, to check that the optimal form selection works for 
extreme cases).
     * Emit short strings inline.  All strings that are shorter than the 
reference size are "short strings".
     * Several passes of simplifying code and moving stuff to more 
private (i.e. more writer-specific) places.  Certain pieces of code may 
have to be reintroduced later, but now they are overkill and just 
obfuscate the code.
     * dwarf_64 is used throughout.  If value doesn't fit into form that 
could be expanded by having dwarf_64==true, an exception is thrown.
     * Found a bug that causes that DW_AT_sibling would be emitted 
superfluously or omitted.  It turned out that my understanding of 
_m_with_sibling was wrong, and that _m_w_s[true] and _m_w_s[false] can 
be true simultaneously.  Well, that explains the data type used. 
Somehow I managed to get lost in the code for the rest of Friday, unable 
to get it right, hitting obscure errors.

It's all on pmachata/dwarf-writer.

This week
---------

Already done:
     * Fix that stupid problem from Friday.  I just scratched and 
rewrote it and it worked basically on the first try.  Don't know what 
the big deal was.
     * Merge in dwarf branch.

Rest of the week:

We now emit strings and numbers with optimal forms.
  - Implement duplicate pruning, right now each die gets its own abbrev.
  - FYI, no computation is done whether it is advantageous to emit the 
abbrev in the first place (i.e. whether the savings of extra form 
outweigh price of the abbrev itself).  That problem won't be tackled on 
Roland's advice.

When the above is done, next thing might be optimizing references.  For 
things we can't optimize, references including, we now pick the biggest 
form available.  We can shrink these fields afterwards.  But the 
codebase is not ready for this, e.g. gaps have to be able to move, size 
of ElfData has to be patched, etc.  So perhaps work on preparing these 
bits, they will be useful later.

Another option is work on making the produced data complete and 
well-defined enough for consumption by libdw.  That may require emitting 
some tables in addition to .debug_info, .debug_abbrev and .debug_str.

PM