226 lines
9.9 KiB
Plaintext
226 lines
9.9 KiB
Plaintext
# Copyright 2002, 2004, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
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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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#
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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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#
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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 file is part of the gdb testsuite
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# Looking up methods by name, in programs with multiple compilation units.
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# ====== PLEASE BE VERY CAREFUL WHEN CHANGING THIS TEST. =====
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#
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# The bug we're testing for (circa October 2002) is very sensitive to
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# various conditions that are hard to control directly in the test
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# suite. If you change the test, please revert this change, and make
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# sure the test still fails:
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#
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# 2002-08-29 Jim Blandy <jimb@redhat.com>
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#
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# * symtab.c (lookup_symbol_aux): In the cases where we find a
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# minimal symbol of an appropriate name and use its address to
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# select a symtab to read and search, use `name' (as passed to us)
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# as the demangled name when searching the symtab's global and
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# static blocks, not the minsym's name.
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#
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# The original bug was that you'd try to set a breakpoint on a method
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# (e.g., `break s::method1'), and you'd get an error, but if you
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# repeated the command, it would work the second time:
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#
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# (gdb) break s::method1
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# the class s does not have any method named method1
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# Hint: try 's::method1<TAB> or 's::method1<ESC-?>
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# (Note leading single quote.)
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# (gdb) break s::method1
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# Breakpoint 1 at 0x804841b: file psmang1.cc, line 13.
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# (gdb)
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#
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# We observed this bug first using Stabs, and then using Dwarf 2.
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#
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# The problem was in lookup_symbol_aux: when looking up s::method1, it
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# would fail to find it in any symtabs, find the minsym with the
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# corresponding mangled name (say, `_ZN1S7method1Ev'), pass the
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# minsym's address to find_pc_sect_symtab to look up the symtab
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# (causing the compilation unit's full symbols to be read in), and
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# then look up the symbol in that symtab's global block. All that is
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# correct. However, it would pass the minsym's name as the NAME
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# argument to lookup_block_symbol; a minsym's name is mangled, whereas
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# lookup_block_symbol's NAME argument should be demangled.
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#
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# This is a pretty simple bug, but it turns out to be a bear to
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# construct a test for. That's why this test case is so delicate. If
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# you can see how to make it less so, please contribute a patch.
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#
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# Here are the twists:
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#
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# The bug only manifests itself when we call lookup_symbol to look up
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# a method name (like "s::method1" or "s::method2"), and that method's
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# definition is in a compilation unit for which we have read partial
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# symbols, but not full symbols. The partial->full conversion must be
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# caused by that specific lookup. (If we already have full symbols
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# for the method's compilation unit, we won't need to look up the
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# minsym, find the symtab for the minsym's address, and then call
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# lookup_block_symbol; it's that last call where things go awry.)
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#
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# Now, when asked to set a breakpoint at `s::method1', GDB will first
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# look up `s' to see if that is, in fact, the name of a class, and
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# then look up 's::method1'. So we have to make sure that looking up
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# `s' doesn't cause full symbols to be read for the compilation unit
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# containing the definition of `s::method1'.
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#
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# The partial symbol tables for `psmang1.cc' and `psmang2.cc' will
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# both have entries for `s'; GDB will read full symbols for whichever
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# compilation unit's partial symbol table appears first in the
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# objfile's list. The order in which compilation units appear in the
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# partial symbol table list depends on how the program is linked, and
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# how the debug info reader does the partial symbol scan. Ideally,
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# the test shouldn't rely on them appearing in any particular order.
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#
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# So, since we don't know which compilation unit's full symbols are
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# going to get read, we simply try looking up one method from each of
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# the two compilation units. One of them has to come after the other
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# in the partial symbol table list, so whichever comes later will
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# still need its partial symbols read by the time we go to look up
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# 's::methodX'.
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#
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# Second twist: don't move the common definition of `struct s' into a
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# header file. If the compiler emits identical stabs for the
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# #inclusion of that header file into psmang1.cc and into psmang2.cc,
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# then the linker will do stabs compression, and replace one of the
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# BINCL/EINCL regions with an EXCL stab, pointing to the other
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# BINCL/EINCL region. GDB will read this, and record that the
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# compilation unit that got the EXCL depends on the compilation unit
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# that kept the BINCL/EINCL. Then, when it decides it needs to read
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# full symbols for the former, it'll also read full symbols for the
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# latter. Now, if it just so happens that the compilation unit that
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# got the EXCL is also the first one with a definition of `s' in the
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# partial symbol table list, then that first probe for `s' will cause
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# both compilation units' full symbols to be read --- again defeating
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# the test.
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#
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# We could work around this by having three compilation units, or by
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# ensuring that the header file produces different stabs each time
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# it's #included, but it seems simplest just to avoid compilation unit
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# dependencies altogether, drop the header file, and duplicate the
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# (pretty trivial) struct definition.
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#
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# Note that #including any header file at all into both compilation
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# units --- say, <stdio.h> --- could create this sort of dependency.
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#
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# This is the aspect of the test which the debug format is most likely
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# to affect, I think. The different formats create different kinds of
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# inter-CU dependencies, which could mask the bug. It might be
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# possible for the test to check that at least one of the partial
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# symtabs remains unread, and fail otherwise --- the failure
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# indicating that the test itself isn't going to catch the bug it was
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# meant to, not that GDB is misbehaving.
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#
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# Third twist: given the way lookup_block_symbol is written, it's
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# possible to find the symbol even when it gets passed a mangled name
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# for its NAME parameter. There are three ways lookup_block_symbol
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# might search a block, depending on how it was constructed:
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#
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# linear search. In this case, this bug will never manifest itself,
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# since we check every symbol against NAME using SYMBOL_MATCHES_NAME.
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# Since that macro checks its second argument (NAME) against both the
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# mangled and demangled names of the symbol, this will always find the
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# symbol successfully, so, no bug.
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#
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# hash table. If both the mangled and demangled names hash to the
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# same bucket, then you'll again find the symbol "by accident", since
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# we search the entire bucket using SYMBOL_SOURCE_NAME. Since GDB
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# chooses the number of buckets based on the number of symbols, small
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# compilation units may have only one hash bucket; in this case, the
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# search always succeeds, even though we hashed on the wrong name.
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# This test works around that by having a lot of dummy variables,
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# making it less likely that the mangled and demangled names fall in
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# the same bucket.
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#
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# binary search. (GDB 5.2 produced these sorts of blocks, and this
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# test tries to detect the bug there, but subsequent versions of GDB
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# almost never build them, and they may soon be removed entirely.) In
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# this case, the symbols in the block are sorted by their
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# SYMBOL_SOURCE_NAME (whose behavior depends on the current demangling
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# setting, so that's wrong, but let's try to stay focussed).
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# lookup_block_symbol does a binary search comparing NAME with
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# SYMBOL_SOURCE_NAME until the range has been narrowed down to only a
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# few symbols; then it starts a linear search forward from the lower
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# end of that range, until it reaches a symbol whose
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# SYMBOL_SOURCE_NAME follows NAME in lexicographic order. This means
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# that, if you're doing a binary search for a mangled name in a block
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# sorted by SYMBOL_SOURCE_NAME, you might find the symbol `by
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# accident' if the mangled and demangled names happen to fall near
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# each other in the ordering. The initial version of this patch used
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# a class called `S'; all the other symbols in the compilation unit
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# started with lower-case letters, so the demangled name `S::method1'
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# sorted at the same place as the mangled name `_ZN1S7method1Ev': at
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# the very beginning. Using a lower-case 's' as the name ensures that
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# the demangled name falls after all the dummy symbols introduced for
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# the hash table, as described above.
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#
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# This is all so tortured, someone will probably come up with still
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# other ways this test could fail to do its job. If you need to make
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# revisions, please be very careful.
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if $tracelevel then {
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strace $tracelevel
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}
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#
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# test running programs
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#
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set prms_id 0
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set bug_id 0
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if { [skip_cplus_tests] } { continue }
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set testfile "psmang"
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set binfile ${objdir}/${subdir}/${testfile}
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if [get_compiler_info ${binfile} "c++"] {
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return -1;
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}
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if { [gdb_compile "${srcdir}/${subdir}/${testfile}1.cc" "${testfile}1.o" object {debug c++}] != "" } {
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untested psmang.exp
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return -1
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}
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if { [gdb_compile "${srcdir}/${subdir}/${testfile}2.cc" "${testfile}2.o" object {debug c++}] != "" } {
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untested psmang.exp
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return -1
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}
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if { [gdb_compile "${testfile}1.o ${testfile}2.o" ${binfile} executable {debug c++}] != "" } {
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untested psmang.exp
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return -1
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}
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gdb_exit
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gdb_start
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gdb_reinitialize_dir $srcdir/$subdir
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gdb_load ${binfile}
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gdb_test "break s::method1" "Breakpoint .* at .*: file .*psmang1.cc.*"
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# We have to exit and restart GDB here, to make sure that all the
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# compilation units are psymtabs again.
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gdb_exit
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gdb_start
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gdb_reinitialize_dir $srcdir/$subdir
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gdb_load ${binfile}
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gdb_test "break s::method2" "Breakpoint .* at .*: file .*psmang2.cc.*"
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