From 8c83177441405ace08650d9d36f76311009c2ed3 Mon Sep 17 00:00:00 2001 From: Tom Tromey Date: Mon, 2 Nov 2020 17:35:51 -0700 Subject: Introduce DWARF abbrev cache The replacement for the DWARF psymbol reader works in a somewhat different way. The current reader reads and stores all the DIEs that might be interesting. Then, if it is missing a DIE, it re-scans the CU and reads them all. This approach is used for both intra- and inter-CU references. I instrumented the partial DIE hash to see how frequently it was used: [ 0] -> 1538165 [ 1] -> 4912 [ 2] -> 96102 [ 3] -> 175 [ 4] -> 244 That is, most DIEs are never used, and some are looked up twice -- but this is just an artifact of the implementation of partial_die_info::fixup, which may do two lookups. Based on this, the new implementation doesn't try to store any DIEs, but instead just re-scans them on demand. In order to do this, though, it is convenient to have a cache of DWARF abbrevs. This way, if a second CU is needed to resolve an inter-CU reference, the abbrevs for that CU need only be computed a single time. --- gdb/dwarf2/abbrev-cache.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 65 insertions(+) create mode 100644 gdb/dwarf2/abbrev-cache.c (limited to 'gdb/dwarf2/abbrev-cache.c') diff --git a/gdb/dwarf2/abbrev-cache.c b/gdb/dwarf2/abbrev-cache.c new file mode 100644 index 0000000..2168f92 --- /dev/null +++ b/gdb/dwarf2/abbrev-cache.c @@ -0,0 +1,65 @@ +/* DWARF 2 abbrev table cache + + Copyright (C) 2022 Free Software Foundation, Inc. + + This file is part of GDB. + + This program is free software; you can redistribute it and/or modify + it under the terms of the GNU General Public License as published by + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program. If not, see . */ + +#include "defs.h" +#include "dwarf2/read.h" +#include "dwarf2/abbrev-cache.h" + +/* Hash function for an abbrev table. */ + +hashval_t +abbrev_cache::hash_table (const void *item) +{ + const struct abbrev_table *table = (const struct abbrev_table *) item; + return to_underlying (table->sect_off); +} + +/* Comparison function for abbrev table. */ + +int +abbrev_cache::eq_table (const void *lhs, const void *rhs) +{ + const struct abbrev_table *l_table = (const struct abbrev_table *) lhs; + const search_key *key = (const search_key *) rhs; + return (l_table->section == key->section + && l_table->sect_off == key->offset); +} + +abbrev_cache::abbrev_cache () + : m_tables (htab_create_alloc (20, hash_table, eq_table, + htab_delete_entry, + xcalloc, xfree)) +{ +} + +void +abbrev_cache::add (abbrev_table_up table) +{ + /* We allow this as a convenience to the caller. */ + if (table == nullptr) + return; + + search_key key = { table->section, table->sect_off }; + void **slot = htab_find_slot_with_hash (m_tables.get (), &key, + to_underlying (table->sect_off), + INSERT); + /* If this one already existed, then it should have been reused. */ + gdb_assert (*slot == nullptr); + *slot = (void *) table.release (); +} -- cgit v1.1