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.
2020-11-03 08:35:51 +08:00
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/* DWARF abbrev table cache
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Copyright (C) 2022 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#ifndef GDB_DWARF2_ABBREV_CACHE_H
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#define GDB_DWARF2_ABBREV_CACHE_H
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#include "dwarf2/abbrev.h"
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#include "gdbtypes.h"
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2022-04-17 03:58:34 +08:00
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/* An abbrev cache holds abbrev tables for easier reuse. */
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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.
2020-11-03 08:35:51 +08:00
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class abbrev_cache
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{
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public:
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abbrev_cache ();
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DISABLE_COPY_AND_ASSIGN (abbrev_cache);
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2022-04-17 03:58:34 +08:00
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/* Find an abbrev table coming from the abbrev section SECTION at
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offset OFFSET. Return the table, or nullptr if it has not yet
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been registered. */
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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.
2020-11-03 08:35:51 +08:00
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abbrev_table *find (struct dwarf2_section_info *section, sect_offset offset)
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{
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search_key key = { section, offset };
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return (abbrev_table *) htab_find_with_hash (m_tables.get (), &key,
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to_underlying (offset));
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}
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2022-04-17 03:58:34 +08:00
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/* Add TABLE to this cache. Ownership of TABLE is transferred to
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the cache. Note that a table at a given section+offset may only
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be registered once -- a violation of this will cause an assert.
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To avoid this, call the 'find' method first, to see if the table
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has already been read. */
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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.
2020-11-03 08:35:51 +08:00
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void add (abbrev_table_up table);
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private:
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static hashval_t hash_table (const void *item);
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static int eq_table (const void *lhs, const void *rhs);
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struct search_key
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{
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struct dwarf2_section_info *section;
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sect_offset offset;
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};
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/* Hash table of abbrev tables. */
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htab_up m_tables;
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};
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#endif /* GDB_DWARF2_ABBREV_CACHE_H */
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