I was curious about DWARF abbrev table efficiency the other day, so I instrumented gdb to record some simple stats about abbrevs: how many are seen, how many duplicates are seen, and how many bytes are used.

Running gdb on itself, I discovered that abbrevs are largely redundant. In particular, removing redundant abbrevs will remove 95% of abbrevs (10238 unique of 230714 total). Similarly the size of the abbrev tables reduces similarly (230714 bytes needed for the de-duplicated abbrevs, compared to 3848152 as seen in the executable).

Something to think about when you consider the effort DWARF puts in to save a single byte in .debug_info, say by using a 1-byte form rather than a uleb.

I was considering having gdb intern abbrevs and pre-reading all abbrevs so that later steps wouldn’t have to re-read these; but interning turns out to be too slow and so re-reading on demand seems like the way to go.