[Bug mi/23042] typedef resolution traverses all CUs for MI var-create

["vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=23042

--- Comment #5 from Tom de Vries <vries at gcc dot gnu.org> ---
My best guess is: if some of those shared libraries are build with gold
.gdb_index, but not with -ggnu-pubnames (implied by -gsplit-dwarf), you get
"[global, no info]" .gdb_index entries, also for size_t.

So, if a shared lib has 100 CUs, each defining size_t, and the .gdb_index has
"[global, no info]" entries for each of those, then when executing
dw2_lookup_symbol for size_t with block_index GLOBAL_BLOCK:
- the dw2_symtab_iter_next will return the CU for the first entry
- dw2_instantiate_symtab is called for that CU
- block_find_symbol is called, which fails because size_t is static, not global
- the dw2_symtab_iter_next will return the CU for the next entry
- and so on

The workaround for PR15646 is not activated in this case because !attrs_valid,
which is defined as:
...
      /* Only check the symbol attributes if they're present.                   
         Indices prior to version 7 don't record them,                          
         and indices >= 7 may elide them for certain symbols                    
         (gold does this).  */
      int attrs_valid =
        (dwarf2_per_objfile->per_bfd->index_table->version >= 7
         && symbol_kind != GDB_INDEX_SYMBOL_KIND_NONE);
...

I'm currently preparing a patch to limit the scope of the workaround to
symbol_kind == GDB_INDEX_SYMBOL_KIND_TYPE, because in some cases we do want
symbol lookup to find multiple version of a symbol.

Extending the workaround to GDB_INDEX_SYMBOL_KIND_NONE would break that (and
other things as well, I guess, given that we cannot tell global and static
apart).

We could try harder in dw2_lookup_symbol, by iterating twice, first using all
but GDB_INDEX_SYMBOL_KIND_NONE symbols, and then the GDB_INDEX_SYMBOL_KIND_NONE
ones. But that wouldn't help for this case.

We could do a scan of a .gdb_index, find all untyped entries, and revert back
to  partial symbols for those ones.

With a less fine granularity, we could do a scan of a .gdb_index, and upon
finding one untyped entry, revert to partial symbols for the whole objfile. 
But as comment 4 shows, that would make gold --gdb-index unusable on my system,
unless I modify the glibc package to build elf-init.c using -ggnu-pubnames.

That fastest solution obviously would be to make sure that gold -gdb-index is
always paired with -ggnu-pubnames.

-- 
You are receiving this mail because:
You are on the CC list for the bug.