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> I don't really know just how much LLDB cares about fixed-size forms/DIEs,
> but rumor has it it's important to some degree, so I continue to have a
> slight preference towards fixed size representations (or at least having
> the option to do so, even if there are variable length forms too - as
> with addrx).Greg Clayton has told me it's a performance win for loading .debug_info. They can index fixed-size DIEs without actually parsing them. When I proposed the fixed-size strx/addrx forms to the committee, I did some data collection on the effect of strx and addrx. Converting to strx meant fixed size DIEs went from 90-ish to 55-ish percent of all DIEs, so fixed-size strxN forms were definitely worthwhile. The equivalent analysis for addrx showed a difference of more like 4%, which was enough to persuade the committee that would be worthwhile also. If we go with the low_pc-as-range idea then adding fixed-size versions of rnglistx in DWARF 6 would not be a problem. The advantage of what the ranges idea is it can all be done using exiting DWARF 5 features. > at that point I wouldn't mind a form that was two ULEBs (addrx + offset). Might as well just allow DW_AT_low_pc to use a location expression? DW_OP_addrx <n> DW_OP_constx <offset> DW_OP_plus This would be way more acceptable than a new special-purpose form. Still bigger than a new form, of course, but as I noted above only 4% of DIEs become variable size so that penalty doesn't seem excessive. 3 bytes plus 3 LEBs, so only 3 bytes + 1 LEB more than the new form, and still cheaper than the ranges idea. --paulr _______________________________________________ Dwarf-Discuss mailing list Dwarf-Discuss@lists.dwarfstd.org http://lists.dwarfstd.org/listinfo.cgi/dwarf-discuss-dwarfstd.org
