On Fri, 01 Dec 2017 13:02:42 +0100, Pavel Labath wrote:
> > I expect because LLDB does not have any Linux DWARF index support, it has
> > only some Apple OSX index support. GDB's `.debug_index` is not usable for
> > LLDB as it does not contain DIE offsets. I would like to implement DWARF-5
> > `.debug_names` for it later.
>
> Well... missing dwarf index can make things slower, as we will have to
> index things ourselves, but it should not make us hang. (That's not
> say .debug_index support would not be a great feature to have).
FYI the GDB one is `.gdb_index`, I made a typo. But it is not usable for LLDB
as LLDB needs also DIE offsets; GDB expands whole CUs.
DWARF-5 '.debug_names' producer could be even ported from GDB to LLDB
[PATCH v3 0/5] DWARF-5: .debug_names index
https://sourceware.org/ml/gdb-patches/2017-06/msg00541.html
although the consumer is too GDB-specific, LLDB would need its own one.
Although then it would be better==faster to produce per-CU index already by
compiler and a linker could just merge them. In Fedora people use gold now
for C++ as GNU ld is unusable from performance point of view. gold can also
generate .gdb_index on its own but it has to index all the CUs as there is no
per-CU index provided by GCC (or clang?).
0m 5.389s -fuse-ld=gold -Wl,--gdb-index,--build-id
0m 3.564s -fuse-ld=gold -Wl,--build-id
1.825s = --gdb-index part of gold
0m19.401s (GNU ld) -Wl,--build-id
0m 4.364s gdb-add-index
23.765s = GNU ld + gdb-add-index
But then I see lld already supports even -gdb-index. Any updates about LLVM
DWARF index plan is welcome.
Jan
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