1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
|
# Copyright 2002-2017 Free Software Foundation, Inc.
# 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/>.
# This file is part of the gdb testsuite
# Looking up methods by name, in programs with multiple compilation units.
# ====== PLEASE BE VERY CAREFUL WHEN CHANGING THIS TEST. =====
#
# The bug we're testing for (circa October 2002) is very sensitive to
# various conditions that are hard to control directly in the test
# suite. If you change the test, please revert this change, and make
# sure the test still fails:
#
# 2002-08-29 Jim Blandy <jimb@redhat.com>
#
# * symtab.c (lookup_symbol_aux): In the cases where we find a
# minimal symbol of an appropriate name and use its address to
# select a symtab to read and search, use `name' (as passed to us)
# as the demangled name when searching the symtab's global and
# static blocks, not the minsym's name.
#
# The original bug was that you'd try to set a breakpoint on a method
# (e.g., `break s::method1'), and you'd get an error, but if you
# repeated the command, it would work the second time:
#
# (gdb) break s::method1
# the class s does not have any method named method1
# Hint: try 's::method1<TAB> or 's::method1<ESC-?>
# (Note leading single quote.)
# (gdb) break s::method1
# Breakpoint 1 at 0x804841b: file psmang1.cc, line 13.
# (gdb)
#
# We observed this bug first using Stabs, and then using Dwarf 2.
#
# The problem was in lookup_symbol_aux: when looking up s::method1, it
# would fail to find it in any symtabs, find the minsym with the
# corresponding mangled name (say, `_ZN1S7method1Ev'), pass the
# minsym's address to find_pc_sect_symtab to look up the symtab
# (causing the compilation unit's full symbols to be read in), and
# then look up the symbol in that symtab's global block. All that is
# correct. However, it would pass the minsym's name as the NAME
# argument to lookup_block_symbol; a minsym's name is mangled, whereas
# lookup_block_symbol's NAME argument should be demangled.
#
# This is a pretty simple bug, but it turns out to be a bear to
# construct a test for. That's why this test case is so delicate. If
# you can see how to make it less so, please contribute a patch.
#
# Here are the twists:
#
# The bug only manifests itself when we call lookup_symbol to look up
# a method name (like "s::method1" or "s::method2"), and that method's
# definition is in a compilation unit for which we have read partial
# symbols, but not full symbols. The partial->full conversion must be
# caused by that specific lookup. (If we already have full symbols
# for the method's compilation unit, we won't need to look up the
# minsym, find the symtab for the minsym's address, and then call
# lookup_block_symbol; it's that last call where things go awry.)
#
# Now, when asked to set a breakpoint at `s::method1', GDB will first
# look up `s' to see if that is, in fact, the name of a class, and
# then look up 's::method1'. So we have to make sure that looking up
# `s' doesn't cause full symbols to be read for the compilation unit
# containing the definition of `s::method1'.
#
# The partial symbol tables for `psmang1.cc' and `psmang2.cc' will
# both have entries for `s'; GDB will read full symbols for whichever
# compilation unit's partial symbol table appears first in the
# objfile's list. The order in which compilation units appear in the
# partial symbol table list depends on how the program is linked, and
# how the debug info reader does the partial symbol scan. Ideally,
# the test shouldn't rely on them appearing in any particular order.
#
# So, since we don't know which compilation unit's full symbols are
# going to get read, we simply try looking up one method from each of
# the two compilation units. One of them has to come after the other
# in the partial symbol table list, so whichever comes later will
# still need its partial symbols read by the time we go to look up
# 's::methodX'.
#
# Second twist: don't move the common definition of `struct s' into a
# header file. If the compiler emits identical stabs for the
# #inclusion of that header file into psmang1.cc and into psmang2.cc,
# then the linker will do stabs compression, and replace one of the
# BINCL/EINCL regions with an EXCL stab, pointing to the other
# BINCL/EINCL region. GDB will read this, and record that the
# compilation unit that got the EXCL depends on the compilation unit
# that kept the BINCL/EINCL. Then, when it decides it needs to read
# full symbols for the former, it'll also read full symbols for the
# latter. Now, if it just so happens that the compilation unit that
# got the EXCL is also the first one with a definition of `s' in the
# partial symbol table list, then that first probe for `s' will cause
# both compilation units' full symbols to be read --- again defeating
# the test.
#
# We could work around this by having three compilation units, or by
# ensuring that the header file produces different stabs each time
# it's #included, but it seems simplest just to avoid compilation unit
# dependencies altogether, drop the header file, and duplicate the
# (pretty trivial) struct definition.
#
# Note that #including any header file at all into both compilation
# units --- say, <stdio.h> --- could create this sort of dependency.
#
# This is the aspect of the test which the debug format is most likely
# to affect, I think. The different formats create different kinds of
# inter-CU dependencies, which could mask the bug. It might be
# possible for the test to check that at least one of the partial
# symtabs remains unread, and fail otherwise --- the failure
# indicating that the test itself isn't going to catch the bug it was
# meant to, not that GDB is misbehaving.
#
# Third twist: given the way lookup_block_symbol is written, it's
# possible to find the symbol even when it gets passed a mangled name
# for its NAME parameter. There are three ways lookup_block_symbol
# might search a block, depending on how it was constructed:
#
# linear search. In this case, this bug will never manifest itself,
# since we check every symbol against NAME using SYMBOL_MATCHES_NAME.
# Since that macro checks its second argument (NAME) against both the
# mangled and demangled names of the symbol, this will always find the
# symbol successfully, so, no bug.
#
# hash table. If both the mangled and demangled names hash to the
# same bucket, then you'll again find the symbol "by accident", since
# we search the entire bucket using SYMBOL_SOURCE_NAME. Since GDB
# chooses the number of buckets based on the number of symbols, small
# compilation units may have only one hash bucket; in this case, the
# search always succeeds, even though we hashed on the wrong name.
# This test works around that by having a lot of dummy variables,
# making it less likely that the mangled and demangled names fall in
# the same bucket.
#
# binary search. (GDB 5.2 produced these sorts of blocks, and this
# test tries to detect the bug there, but subsequent versions of GDB
# almost never build them, and they may soon be removed entirely.) In
# this case, the symbols in the block are sorted by their
# SYMBOL_SOURCE_NAME (whose behavior depends on the current demangling
# setting, so that's wrong, but let's try to stay focussed).
# lookup_block_symbol does a binary search comparing NAME with
# SYMBOL_SOURCE_NAME until the range has been narrowed down to only a
# few symbols; then it starts a linear search forward from the lower
# end of that range, until it reaches a symbol whose
# SYMBOL_SOURCE_NAME follows NAME in lexicographic order. This means
# that, if you're doing a binary search for a mangled name in a block
# sorted by SYMBOL_SOURCE_NAME, you might find the symbol `by
# accident' if the mangled and demangled names happen to fall near
# each other in the ordering. The initial version of this patch used
# a class called `S'; all the other symbols in the compilation unit
# started with lower-case letters, so the demangled name `S::method1'
# sorted at the same place as the mangled name `_ZN1S7method1Ev': at
# the very beginning. Using a lower-case 's' as the name ensures that
# the demangled name falls after all the dummy symbols introduced for
# the hash table, as described above.
#
# This is all so tortured, someone will probably come up with still
# other ways this test could fail to do its job. If you need to make
# revisions, please be very careful.
#
# test running programs
#
if { [skip_cplus_tests] } { continue }
standard_testfile psmang1.cc psmang2.cc
if [get_compiler_info "c++"] {
return -1
}
if {[prepare_for_testing "failed to prepare" $testfile \
[list $srcfile $srcfile2] {debug c++}]} {
return -1
}
gdb_test "break s::method1" "Breakpoint .* at .*: file .*psmang1.cc.*"
# We have to exit and restart GDB here, to make sure that all the
# compilation units are psymtabs again.
clean_restart ${binfile}
gdb_test "break s::method2" "Breakpoint .* at .*: file .*psmang2.cc.*"
|
