On Wed, Jul 26, 2017 at 12:56 PM Robinson, Paul <paul.robin...@sony.com> wrote:
> >> 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? > Right > 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. > Fair point/question (I was going to say I wasn't sure if gdb supported rnglists yet, but grepping the source it looks like it probably does - though LLVM can't/doesn't produce them yet, it would be a good thing, even aside from this particular issue). Certainly would be a thing to prototype/a valid representation that would reduce the number of address relocations/size of object files (under split DWARF at least). But I imagine that representation might be a bit larger overall/more expensive to parse? - Dave
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