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61baf725 | 1 | # Copyright 2002-2017 Free Software Foundation, Inc. |
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2 | |
3 | # This program is free software; you can redistribute it and/or modify | |
4 | # it under the terms of the GNU General Public License as published by | |
e22f8b7c | 5 | # the Free Software Foundation; either version 3 of the License, or |
f0708dbb | 6 | # (at your option) any later version. |
e22f8b7c | 7 | # |
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8 | # This program is distributed in the hope that it will be useful, |
9 | # but WITHOUT ANY WARRANTY; without even the implied warranty of | |
10 | # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
11 | # GNU General Public License for more details. | |
e22f8b7c | 12 | # |
f0708dbb | 13 | # You should have received a copy of the GNU General Public License |
e22f8b7c | 14 | # along with this program. If not, see <http://www.gnu.org/licenses/>. |
f0708dbb | 15 | |
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16 | # This file is part of the gdb testsuite |
17 | ||
18 | # Looking up methods by name, in programs with multiple compilation units. | |
19 | ||
20 | # ====== PLEASE BE VERY CAREFUL WHEN CHANGING THIS TEST. ===== | |
21 | # | |
22 | # The bug we're testing for (circa October 2002) is very sensitive to | |
23 | # various conditions that are hard to control directly in the test | |
24 | # suite. If you change the test, please revert this change, and make | |
25 | # sure the test still fails: | |
26 | # | |
27 | # 2002-08-29 Jim Blandy <jimb@redhat.com> | |
28 | # | |
29 | # * symtab.c (lookup_symbol_aux): In the cases where we find a | |
30 | # minimal symbol of an appropriate name and use its address to | |
31 | # select a symtab to read and search, use `name' (as passed to us) | |
32 | # as the demangled name when searching the symtab's global and | |
33 | # static blocks, not the minsym's name. | |
34 | # | |
35 | # The original bug was that you'd try to set a breakpoint on a method | |
36 | # (e.g., `break s::method1'), and you'd get an error, but if you | |
37 | # repeated the command, it would work the second time: | |
38 | # | |
39 | # (gdb) break s::method1 | |
40 | # the class s does not have any method named method1 | |
41 | # Hint: try 's::method1<TAB> or 's::method1<ESC-?> | |
42 | # (Note leading single quote.) | |
43 | # (gdb) break s::method1 | |
44 | # Breakpoint 1 at 0x804841b: file psmang1.cc, line 13. | |
45 | # (gdb) | |
46 | # | |
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47 | # We observed this bug first using Stabs, and then using Dwarf 2. |
48 | # | |
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49 | # The problem was in lookup_symbol_aux: when looking up s::method1, it |
50 | # would fail to find it in any symtabs, find the minsym with the | |
51 | # corresponding mangled name (say, `_ZN1S7method1Ev'), pass the | |
52 | # minsym's address to find_pc_sect_symtab to look up the symtab | |
53 | # (causing the compilation unit's full symbols to be read in), and | |
54 | # then look up the symbol in that symtab's global block. All that is | |
55 | # correct. However, it would pass the minsym's name as the NAME | |
56 | # argument to lookup_block_symbol; a minsym's name is mangled, whereas | |
57 | # lookup_block_symbol's NAME argument should be demangled. | |
58 | # | |
59 | # This is a pretty simple bug, but it turns out to be a bear to | |
60 | # construct a test for. That's why this test case is so delicate. If | |
61 | # you can see how to make it less so, please contribute a patch. | |
62 | # | |
63 | # Here are the twists: | |
64 | # | |
65 | # The bug only manifests itself when we call lookup_symbol to look up | |
66 | # a method name (like "s::method1" or "s::method2"), and that method's | |
67 | # definition is in a compilation unit for which we have read partial | |
68 | # symbols, but not full symbols. The partial->full conversion must be | |
69 | # caused by that specific lookup. (If we already have full symbols | |
70 | # for the method's compilation unit, we won't need to look up the | |
71 | # minsym, find the symtab for the minsym's address, and then call | |
72 | # lookup_block_symbol; it's that last call where things go awry.) | |
73 | # | |
74 | # Now, when asked to set a breakpoint at `s::method1', GDB will first | |
75 | # look up `s' to see if that is, in fact, the name of a class, and | |
76 | # then look up 's::method1'. So we have to make sure that looking up | |
77 | # `s' doesn't cause full symbols to be read for the compilation unit | |
78 | # containing the definition of `s::method1'. | |
79 | # | |
80 | # The partial symbol tables for `psmang1.cc' and `psmang2.cc' will | |
81 | # both have entries for `s'; GDB will read full symbols for whichever | |
82 | # compilation unit's partial symbol table appears first in the | |
83 | # objfile's list. The order in which compilation units appear in the | |
84 | # partial symbol table list depends on how the program is linked, and | |
85 | # how the debug info reader does the partial symbol scan. Ideally, | |
86 | # the test shouldn't rely on them appearing in any particular order. | |
87 | # | |
88 | # So, since we don't know which compilation unit's full symbols are | |
89 | # going to get read, we simply try looking up one method from each of | |
90 | # the two compilation units. One of them has to come after the other | |
91 | # in the partial symbol table list, so whichever comes later will | |
92 | # still need its partial symbols read by the time we go to look up | |
93 | # 's::methodX'. | |
94 | # | |
95 | # Second twist: don't move the common definition of `struct s' into a | |
96 | # header file. If the compiler emits identical stabs for the | |
97 | # #inclusion of that header file into psmang1.cc and into psmang2.cc, | |
98 | # then the linker will do stabs compression, and replace one of the | |
99 | # BINCL/EINCL regions with an EXCL stab, pointing to the other | |
100 | # BINCL/EINCL region. GDB will read this, and record that the | |
101 | # compilation unit that got the EXCL depends on the compilation unit | |
102 | # that kept the BINCL/EINCL. Then, when it decides it needs to read | |
103 | # full symbols for the former, it'll also read full symbols for the | |
104 | # latter. Now, if it just so happens that the compilation unit that | |
105 | # got the EXCL is also the first one with a definition of `s' in the | |
106 | # partial symbol table list, then that first probe for `s' will cause | |
107 | # both compilation units' full symbols to be read --- again defeating | |
108 | # the test. | |
109 | # | |
110 | # We could work around this by having three compilation units, or by | |
111 | # ensuring that the header file produces different stabs each time | |
112 | # it's #included, but it seems simplest just to avoid compilation unit | |
113 | # dependencies altogether, drop the header file, and duplicate the | |
114 | # (pretty trivial) struct definition. | |
115 | # | |
116 | # Note that #including any header file at all into both compilation | |
117 | # units --- say, <stdio.h> --- could create this sort of dependency. | |
118 | # | |
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119 | # This is the aspect of the test which the debug format is most likely |
120 | # to affect, I think. The different formats create different kinds of | |
121 | # inter-CU dependencies, which could mask the bug. It might be | |
122 | # possible for the test to check that at least one of the partial | |
123 | # symtabs remains unread, and fail otherwise --- the failure | |
124 | # indicating that the test itself isn't going to catch the bug it was | |
125 | # meant to, not that GDB is misbehaving. | |
126 | # | |
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127 | # Third twist: given the way lookup_block_symbol is written, it's |
128 | # possible to find the symbol even when it gets passed a mangled name | |
129 | # for its NAME parameter. There are three ways lookup_block_symbol | |
130 | # might search a block, depending on how it was constructed: | |
131 | # | |
132 | # linear search. In this case, this bug will never manifest itself, | |
133 | # since we check every symbol against NAME using SYMBOL_MATCHES_NAME. | |
134 | # Since that macro checks its second argument (NAME) against both the | |
135 | # mangled and demangled names of the symbol, this will always find the | |
136 | # symbol successfully, so, no bug. | |
137 | # | |
138 | # hash table. If both the mangled and demangled names hash to the | |
139 | # same bucket, then you'll again find the symbol "by accident", since | |
140 | # we search the entire bucket using SYMBOL_SOURCE_NAME. Since GDB | |
141 | # chooses the number of buckets based on the number of symbols, small | |
142 | # compilation units may have only one hash bucket; in this case, the | |
143 | # search always succeeds, even though we hashed on the wrong name. | |
144 | # This test works around that by having a lot of dummy variables, | |
145 | # making it less likely that the mangled and demangled names fall in | |
146 | # the same bucket. | |
147 | # | |
148 | # binary search. (GDB 5.2 produced these sorts of blocks, and this | |
149 | # test tries to detect the bug there, but subsequent versions of GDB | |
150 | # almost never build them, and they may soon be removed entirely.) In | |
151 | # this case, the symbols in the block are sorted by their | |
152 | # SYMBOL_SOURCE_NAME (whose behavior depends on the current demangling | |
153 | # setting, so that's wrong, but let's try to stay focussed). | |
154 | # lookup_block_symbol does a binary search comparing NAME with | |
155 | # SYMBOL_SOURCE_NAME until the range has been narrowed down to only a | |
156 | # few symbols; then it starts a linear search forward from the lower | |
157 | # end of that range, until it reaches a symbol whose | |
158 | # SYMBOL_SOURCE_NAME follows NAME in lexicographic order. This means | |
159 | # that, if you're doing a binary search for a mangled name in a block | |
160 | # sorted by SYMBOL_SOURCE_NAME, you might find the symbol `by | |
161 | # accident' if the mangled and demangled names happen to fall near | |
162 | # each other in the ordering. The initial version of this patch used | |
163 | # a class called `S'; all the other symbols in the compilation unit | |
164 | # started with lower-case letters, so the demangled name `S::method1' | |
165 | # sorted at the same place as the mangled name `_ZN1S7method1Ev': at | |
166 | # the very beginning. Using a lower-case 's' as the name ensures that | |
167 | # the demangled name falls after all the dummy symbols introduced for | |
168 | # the hash table, as described above. | |
169 | # | |
170 | # This is all so tortured, someone will probably come up with still | |
171 | # other ways this test could fail to do its job. If you need to make | |
172 | # revisions, please be very careful. | |
173 | ||
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174 | # |
175 | # test running programs | |
176 | # | |
177 | ||
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178 | |
179 | if { [skip_cplus_tests] } { continue } | |
180 | ||
f5f3a911 | 181 | standard_testfile psmang1.cc psmang2.cc |
f0708dbb | 182 | |
4c93b1db | 183 | if [get_compiler_info "c++"] { |
ae59b1da | 184 | return -1 |
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185 | } |
186 | ||
5b362f04 | 187 | if {[prepare_for_testing "failed to prepare" $testfile \ |
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188 | [list $srcfile $srcfile2] {debug c++}]} { |
189 | return -1 | |
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190 | } |
191 | ||
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192 | gdb_test "break s::method1" "Breakpoint .* at .*: file .*psmang1.cc.*" |
193 | ||
194 | # We have to exit and restart GDB here, to make sure that all the | |
195 | # compilation units are psymtabs again. | |
196 | ||
f5f3a911 | 197 | clean_restart ${binfile} |
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198 | |
199 | gdb_test "break s::method2" "Breakpoint .* at .*: file .*psmang2.cc.*" |