On Thu, 2018-01-25 at 16:06 +0100, Mark Wielaard wrote: > Currently storing a lot of Dwarf_Dies might be inefficient since it > costs a lot of memory since the sizeof (Dwarf_Die) == 32 bytes on 64bit > arches. You can try storing just the Dwarf_Off from dwarf_dieoffset. > Which is just 8 bytes. But then you have to keep track of whether to > call dwarf_dieoffset, if the Dwarf_Die came from the main .debug_info, > or call dwarf_dieoffset_types, if it came from .debug_types. And you'll > have to keep track of whether it came from the main Dwarf or the alt > Dwarf (dwz multi file). With DWARF5 or GNU DebugFission split-dwarf > you will also need to know which split Dwarf file the original DIE > came from. > > A Dwarf_Die consists of an addr pointer where the actual DIE data > comes from, a CU pointer that provides context (and has a pointer > to the Dwarf file the Die is associated with) and a (cached) > Dwarf_Abbrev pointer that is initialized when the Dwarf_Die is > first read and describes how to interpret the DIE data. > > libdw already keeps track of the data pointers (sections) of a > Dwarf file and given an offset it can already reconstruct the > other Dwarf_Die fields. So this patch introduces dwarf_die_addr_die. > Given a Dwarf_Die addr dwarf_die_addr_die returns a (reconstructed) > Dwarf_Die, or NULL if the given addr didn't come from a valid > Dwarf_Die. In particular it will make sure that the correct Dwarf_CU > pointer is set for the Dwarf_Die, the Dwarf_Abbrev pointer will not > be set up yet (it will only be once the Dwarf_Die is used to read > attributes, children or siblings). > > This functions can be used to keep a reference to a Dwarf_Die which > you want to refer to later. The addr, and the result of this function, > is only valid while the associated Dwarf is valid. > > Since libdw already had to lookup the Dwarf_CU given an offset, this > function is as efficient as dwarf_dieoffset (or dwarf_dieoffset_types) > without having to know the original origin of the Dwarf_Die. It will > search both the .debug_info and .debug_types data sections from both > the main Dwarf or the alt Dwarf file. Once split dwarf support is added > it will also look in any split dwarf .dwo (or the .dwp) file. > > The only limitation, compared to using a Dwarf_Off and dwarf_dieoffset, > is that it only works during runtime while the main Dwarf object is > valid (till dwarf_end has been called on it).
I pushed this to master now.