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From: Tom Tromey <tromey@sourceware.org> To: gdb-cvs@sourceware.org Subject: [binutils-gdb] Introduce DWARF abbrev cache Date: Tue, 12 Apr 2022 15:40:21 +0000 (GMT) [thread overview] Message-ID: <20220412154021.4638D385840C@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=8c83177441405ace08650d9d36f76311009c2ed3 commit 8c83177441405ace08650d9d36f76311009c2ed3 Author: Tom Tromey <tom@tromey.com> Date: Mon Nov 2 17:35:51 2020 -0700 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. Diff: --- gdb/Makefile.in | 1 + gdb/dwarf2/abbrev-cache.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++ gdb/dwarf2/abbrev-cache.h | 58 ++++++++++++++++++++++++++++++++++++++++++ gdb/dwarf2/abbrev.c | 5 ++-- gdb/dwarf2/abbrev.h | 4 ++- 5 files changed, 130 insertions(+), 3 deletions(-) diff --git a/gdb/Makefile.in b/gdb/Makefile.in index 110c157896d..1374f295f8a 100644 --- a/gdb/Makefile.in +++ b/gdb/Makefile.in @@ -1044,6 +1044,7 @@ COMMON_SFILES = \ displaced-stepping.c \ dummy-frame.c \ dwarf2/abbrev.c \ + dwarf2/abbrev-cache.c \ dwarf2/attribute.c \ dwarf2/comp-unit-head.c \ dwarf2/cu.c \ diff --git a/gdb/dwarf2/abbrev-cache.c b/gdb/dwarf2/abbrev-cache.c new file mode 100644 index 00000000000..2168f92dd9d --- /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 <http://www.gnu.org/licenses/>. */ + +#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<abbrev_table>, + 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 (); +} diff --git a/gdb/dwarf2/abbrev-cache.h b/gdb/dwarf2/abbrev-cache.h new file mode 100644 index 00000000000..7af28cd8181 --- /dev/null +++ b/gdb/dwarf2/abbrev-cache.h @@ -0,0 +1,58 @@ +/* DWARF 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 <http://www.gnu.org/licenses/>. */ + +#ifndef GDB_DWARF2_ABBREV_CACHE_H +#define GDB_DWARF2_ABBREV_CACHE_H + +#include "dwarf2/abbrev.h" +#include <unordered_set> +#include "gdbtypes.h" + +class abbrev_cache +{ +public: + abbrev_cache (); + DISABLE_COPY_AND_ASSIGN (abbrev_cache); + + abbrev_table *find (struct dwarf2_section_info *section, sect_offset offset) + { + search_key key = { section, offset }; + + return (abbrev_table *) htab_find_with_hash (m_tables.get (), &key, + to_underlying (offset)); + } + + void add (abbrev_table_up table); + +private: + + static hashval_t hash_table (const void *item); + static int eq_table (const void *lhs, const void *rhs); + + struct search_key + { + struct dwarf2_section_info *section; + sect_offset offset; + }; + + /* Hash table of abbrev tables. */ + htab_up m_tables; +}; + +#endif /* GDB_DWARF2_ABBREV_CACHE_H */ diff --git a/gdb/dwarf2/abbrev.c b/gdb/dwarf2/abbrev.c index 1dd0818c382..4b65e6b5309 100644 --- a/gdb/dwarf2/abbrev.c +++ b/gdb/dwarf2/abbrev.c @@ -58,8 +58,9 @@ eq_abbrev (const void *lhs, const void *rhs) dies from a section we read in all abbreviations and install them in a hash table. */ -abbrev_table::abbrev_table (sect_offset off) +abbrev_table::abbrev_table (sect_offset off, struct dwarf2_section_info *sect) : sect_off (off), + section (sect), m_abbrevs (htab_create_alloc (20, hash_abbrev, eq_abbrev, nullptr, xcalloc, xfree)) { @@ -85,7 +86,7 @@ abbrev_table::read (struct dwarf2_section_info *section, const gdb_byte *abbrev_ptr; struct abbrev_info *cur_abbrev; - abbrev_table_up abbrev_table (new struct abbrev_table (sect_off)); + abbrev_table_up abbrev_table (new struct abbrev_table (sect_off, section)); struct obstack *obstack = &abbrev_table->m_abbrev_obstack; /* Caller must ensure this. */ diff --git a/gdb/dwarf2/abbrev.h b/gdb/dwarf2/abbrev.h index 414296796e3..b5fa76ad514 100644 --- a/gdb/dwarf2/abbrev.h +++ b/gdb/dwarf2/abbrev.h @@ -85,9 +85,11 @@ struct abbrev_table This is used as a sanity check when the table is used. */ const sect_offset sect_off; + struct dwarf2_section_info *section; + private: - explicit abbrev_table (sect_offset off); + abbrev_table (sect_offset off, struct dwarf2_section_info *sect); DISABLE_COPY_AND_ASSIGN (abbrev_table);
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