PR 16253 revisited
Last year a patch was submitted/approved/commited to eliminate
symbol_matches_domain which was causing this problem. It was later reverted
because it introduced a (severe) performance regression.
Recap:
(gdb) list
1 enum e {A,B,C} e;
2 int main (void) { return 0; }
3
(gdb) p e
Attempt to use a type name as an expression
The parser attempts to find a symbol named "e" of VAR_DOMAIN.
This gets passed down through lookup_symbol and (eventually) into
block_lookup_symbol_primary, which iterates over the block's dictionary
of symbols:
for (sym = dict_iter_name_first (block->dict, name, &dict_iter);
sym != NULL;
sym = dict_iter_name_next (name, &dict_iter))
{
if (symbol_matches_domain (SYMBOL_LANGUAGE (sym),
SYMBOL_DOMAIN (sym), domain))
return sym;
}
The problem here is that we have a symbol named "e" in both STRUCT_DOMAIN
and VAR_DOMAIN, and for languages like C++, Java, and Ada, where a tag name
may be used as an implicit typedef of the type, symbol_matches_domain ignores
the difference between VAR_DOMAIN and STRUCT_DOMAIN. As it happens, the
STRUCT_DOMAIN symbol is found first, considered a match, and that symbol is
returned to the parser, eliciting the (now dreaded) error message.
Since this bug exists specifically because we have both STRUCT and VAR_DOMAIN
symbols in a given block/CU, this patch rather simply/naively changes
block_lookup_symbol_primary so that it continues to search for an exact
domain match on the symbol if symbol_matches_domain returns a symbol
which does not exactly match the requested domain.
This "fixes" the immediate problem, but admittedly might uncover other,
related bugs. [Paranoia?] However, it causes no regressions (functional
or performance) in the test suite. A similar change has been made
to block_lookup_symbol for other cases in which this bug might appear.
The tests from the previous submission have been resurrected and updated.
However since we can still be given a matching symbol with a different domain
than requested, we cannot say that a symbol "was not found." The error
messages today will still be the (dreaded) "Attempt to use a type name..."
ChangeLog
PR 16253
* block.c (block_lookup_symbol): For non-function blocks,
continue to search for a symbol with an exact domain match
Otherwise, return any previously found "best domain" symbol.
(block_lookup_symbol_primary): Likewise.
testsuite/ChangeLog
PR 16253
* gdb.cp/var-tag-2.cc: New file.
* gdb.cp/var-tag-3.cc: New file.
* gdb.cp/var-tag-4.cc: New file.
* gdb.cp/var-tag.cc: New file.
* gdb.cp/var-tag.exp: New file.
2015-06-26 19:27:45 +02:00
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/* This testcase is part of GDB, the GNU debugger.
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2017-01-01 07:50:51 +01:00
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Copyright 2015-2017 Free Software Foundation, Inc.
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PR 16253 revisited
Last year a patch was submitted/approved/commited to eliminate
symbol_matches_domain which was causing this problem. It was later reverted
because it introduced a (severe) performance regression.
Recap:
(gdb) list
1 enum e {A,B,C} e;
2 int main (void) { return 0; }
3
(gdb) p e
Attempt to use a type name as an expression
The parser attempts to find a symbol named "e" of VAR_DOMAIN.
This gets passed down through lookup_symbol and (eventually) into
block_lookup_symbol_primary, which iterates over the block's dictionary
of symbols:
for (sym = dict_iter_name_first (block->dict, name, &dict_iter);
sym != NULL;
sym = dict_iter_name_next (name, &dict_iter))
{
if (symbol_matches_domain (SYMBOL_LANGUAGE (sym),
SYMBOL_DOMAIN (sym), domain))
return sym;
}
The problem here is that we have a symbol named "e" in both STRUCT_DOMAIN
and VAR_DOMAIN, and for languages like C++, Java, and Ada, where a tag name
may be used as an implicit typedef of the type, symbol_matches_domain ignores
the difference between VAR_DOMAIN and STRUCT_DOMAIN. As it happens, the
STRUCT_DOMAIN symbol is found first, considered a match, and that symbol is
returned to the parser, eliciting the (now dreaded) error message.
Since this bug exists specifically because we have both STRUCT and VAR_DOMAIN
symbols in a given block/CU, this patch rather simply/naively changes
block_lookup_symbol_primary so that it continues to search for an exact
domain match on the symbol if symbol_matches_domain returns a symbol
which does not exactly match the requested domain.
This "fixes" the immediate problem, but admittedly might uncover other,
related bugs. [Paranoia?] However, it causes no regressions (functional
or performance) in the test suite. A similar change has been made
to block_lookup_symbol for other cases in which this bug might appear.
The tests from the previous submission have been resurrected and updated.
However since we can still be given a matching symbol with a different domain
than requested, we cannot say that a symbol "was not found." The error
messages today will still be the (dreaded) "Attempt to use a type name..."
ChangeLog
PR 16253
* block.c (block_lookup_symbol): For non-function blocks,
continue to search for a symbol with an exact domain match
Otherwise, return any previously found "best domain" symbol.
(block_lookup_symbol_primary): Likewise.
testsuite/ChangeLog
PR 16253
* gdb.cp/var-tag-2.cc: New file.
* gdb.cp/var-tag-3.cc: New file.
* gdb.cp/var-tag-4.cc: New file.
* gdb.cp/var-tag.cc: New file.
* gdb.cp/var-tag.exp: New file.
2015-06-26 19:27:45 +02:00
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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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/* This object is in a separate file so that its debug info is not
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expanded at startup. Once debug info is expanded we are no longer
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exercising block_lookup_symbol, and instead are exercising
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block_lookup_symbol_primary. */
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union U2 {int a; char b;} U2;
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