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3dd9bb4620
I found that these tests:
make check-gdb RUNTESTFLAGS="--target_board=cc-with-gdb-index gdb.base/maint.exp"
make check-gdb RUNTESTFLAGS="--target_board=cc-with-debug-names gdb.base/maint.exp"
were causing GDB to segfault. It turns out that this test runs this
command:
maint print psymbols -pc main /path/to/some/file
which tries to lookup the partial_symtab for 'main'. The problem is
that there is no partial_symtab for 'main' as we are using the
.gdb_index or .debug_names instead of partial_symtabs.
What happens is that maintenance_print_symbols calls
find_pc_sect_psymtab, which looks for the partial_symtab in the
objfile's objfile->partial_symtabs->psymtabs_addrmap.
This is a problem because when we are using the indexes
psymtabs_addrmap is reused to hold things other than partial_symtabs,
this can be seen in dwarf2read.c in create_addrmap_from_index and
create_addrmap_from_aranges. If we then lookup in psymtabs_addrmap we
end up returning a pointer to something that isn't really a
partial_symtab, after which everything goes wrong.
Initially I simply added a check at the start of find_pc_sect_psymtab
that the objfile had some partial_symtabs, like:
if (objfile->partial_symtabs->psymtabs == NULL)
return NULL;
Figuring that if there were no partial_symtabs at all then this
function should always return NULL, however, this caused a failure in
the test gdb.python/py-event.exp which I didn't dig into too deeply,
but seems to be that in this tests there are initially no psymtabs,
but the second part of find_pc_sect_psymtab does manage to read some
in from somewhere, with the check I added the test fails as we
returned NULL here and this caused GDB to load in the full symtabs
earlier than was expected.
Instead I chose to guard only the access to psymtabs_addrmap with a
check that the function has some psymtabs. This allows my original
tests to pass, and the py-event.exp test to pass too.
Now, a good argument can be made that we simply should never call
find_pc_sect_psymtab on an objfile that is using indexes instead of
partial_symtabs. I did consider this approach, we could easily add an
assert into find_pc_sect_psymtab that if we find a partial_symtab in
psymtabs_addrmap then the psymtabs pointer must be non-null. The
responsibility would then be on the user of find_pc_sect_psymtab to
ensure that the objfile being checked is suitable. In the end I
didn't take this approach as the check in find_pc_sect_psymtab is
cheap and this ensures that any future miss-uses of the function will
not cause problems.
I also extended the comment on psymtabs_addrmap to indicate that it
holds more than just partial_symtabs as this was not at all clear from
the original comment, and caused me some confusion when I was
initially debugging this problem.
gdb/ChangeLog:
* psymtab.c (find_pc_sect_psymtab): Move baseaddr local into more
inner scope, add check that the objfile has psymtabs before
checking psymtabs_addrmap.
* psymtab.h (psymtab_storage) <psymtabs_addrmap>: Extend comment.
158 lines
5.0 KiB
C++
158 lines
5.0 KiB
C++
/* Public partial symbol table definitions.
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Copyright (C) 2009-2019 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 PSYMTAB_H
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#define PSYMTAB_H
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#include "gdb_obstack.h"
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#include "symfile.h"
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#include "gdbsupport/next-iterator.h"
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#include "bcache.h"
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struct partial_symbol;
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/* An instance of this class manages the partial symbol tables and
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partial symbols for a given objfile.
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The core psymtab functions -- those in psymtab.c -- arrange for
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nearly all psymtab- and psymbol-related allocations to happen
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either in the psymtab_storage object (either on its obstack or in
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other memory managed by this class), or on the per-BFD object. The
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only link from the psymtab storage object back to the objfile (or
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objfile_obstack) that is made by the core psymtab code is the
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compunit_symtab member in the psymtab.
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However, it is up to each symbol reader to maintain this invariant
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in other ways, if it wants to reuse psymtabs across multiple
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objfiles. The main issue here is ensuring that read_symtab_private
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does not point into objfile_obstack. */
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class psymtab_storage
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{
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public:
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psymtab_storage ();
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~psymtab_storage ();
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DISABLE_COPY_AND_ASSIGN (psymtab_storage);
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/* Discard all partial symbol tables starting with "psymtabs" and
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proceeding until "to" has been discarded. */
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void discard_psymtabs_to (struct partial_symtab *to)
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{
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while (psymtabs != to)
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discard_psymtab (psymtabs);
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}
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/* Discard the partial symbol table. */
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void discard_psymtab (struct partial_symtab *pst);
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/* Return the obstack that is used for storage by this object. */
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struct obstack *obstack ()
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{
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if (!m_obstack.has_value ())
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m_obstack.emplace ();
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return &*m_obstack;
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}
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/* Allocate storage for the "dependencies" field of a psymtab.
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NUMBER says how many dependencies there are. */
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struct partial_symtab **allocate_dependencies (int number)
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{
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return OBSTACK_CALLOC (obstack (), number, struct partial_symtab *);
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}
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/* Allocate a new psymtab on the psymtab obstack. The new psymtab
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will be linked in to the "psymtabs" list, but otherwise all other
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fields will be zero. */
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struct partial_symtab *allocate_psymtab ();
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typedef next_adapter<struct partial_symtab> partial_symtab_range;
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/* A range adapter that makes it possible to iterate over all
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psymtabs in one objfile. */
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partial_symtab_range range ()
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{
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return partial_symtab_range (psymtabs);
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}
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/* Each objfile points to a linked list of partial symtabs derived from
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this file, one partial symtab structure for each compilation unit
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(source file). */
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struct partial_symtab *psymtabs = nullptr;
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/* Map addresses to the entries of PSYMTABS. It would be more efficient to
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have a map per the whole process but ADDRMAP cannot selectively remove
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its items during FREE_OBJFILE. This mapping is already present even for
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PARTIAL_SYMTABs which still have no corresponding full SYMTABs read.
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The DWARF parser reuses this addrmap to store things other than
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psymtabs in the cases where debug information is being read from, for
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example, the .debug-names section. */
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struct addrmap *psymtabs_addrmap = nullptr;
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/* A byte cache where we can stash arbitrary "chunks" of bytes that
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will not change. */
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struct bcache psymbol_cache;
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/* Vectors of all partial symbols read in from file. The actual data
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is stored in the objfile_obstack. */
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std::vector<partial_symbol *> global_psymbols;
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std::vector<partial_symbol *> static_psymbols;
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private:
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/* List of freed partial symtabs, available for re-use. */
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struct partial_symtab *free_psymtabs = nullptr;
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/* The obstack where allocations are made. This is lazily allocated
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so that we don't waste memory when there are no psymtabs. */
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gdb::optional<auto_obstack> m_obstack;
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};
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extern const struct quick_symbol_functions psym_functions;
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extern const struct quick_symbol_functions dwarf2_gdb_index_functions;
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extern const struct quick_symbol_functions dwarf2_debug_names_functions;
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/* Ensure that the partial symbols for OBJFILE have been loaded. If
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VERBOSE is non-zero, then this will print a message when symbols
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are loaded. This function returns a range adapter suitable for
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iterating over the psymtabs of OBJFILE. */
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extern psymtab_storage::partial_symtab_range require_partial_symbols
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(struct objfile *objfile, int verbose);
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#endif /* PSYMTAB_H */
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