[Dwarf-Discuss] address pool + offset representation

Robinson, Paul paul.robinson at sony.com
Wed Jul 26 12:56:21 PDT 2017


>> This discussion is about reducing the number of .debug_addr entries you
>> need, so the place to look would be the "class address" attributes.
>> There aren't all that many of them, and the one most likely to benefit
>> would be DW_AT_low_pc.
>>
>> We made it okay to have DW_AT_high_pc be a constant, which is implicitly
>> the sum of that constant with the same DIE's DW_AT_low_pc value.
>> How about if DW_AT_low_pc could also be a constant, which would be added
>> to the containing block/subprogram's DW_AT_low_pc?
>
> It'd catch a fair few, maybe even most, of the cases - though still
> potentially many more relocations than needed: eg: two (or more)
> functions in the same section would end up using separate relocations
> (assuming they were in a CU with at least one function in some other
> section - such as an inline function in a comdat).

Oh, because the unit wouldn't have a low_pc, it would have ranges?

Well... why not just use ranges, in that case?  .debug_rnglists is
already tuned to reduce relocations.  A range list with only one
entry is the same as a contiguous range, and DW_RLE_offset_pair is
basically the same as using constant low_pc and high_pc.
--paulr



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