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618f726f | 1 | # Copyright 2002-2016 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 |
eb7f1c48 | 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 | # |
eb7f1c48 | 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/>. |
eb7f1c48 | 15 | |
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16 | |
17 | if { [skip_cplus_tests] } { continue } | |
18 | ||
f5f3a911 | 19 | standard_testfile hang1.cc hang2.cc hang3.cc |
eb7f1c48 | 20 | |
f5f3a911 TT |
21 | if {[prepare_for_testing $testfile.exp $testfile \ |
22 | [list $srcfile $srcfile2 $srcfile3] {debug c++}]} { | |
23 | return -1 | |
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24 | } |
25 | ||
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26 | # As of May 1, 2002, GDB hangs trying to read the debug info for the |
27 | # `hang2.o' compilation unit from the executable `hang', when compiled | |
28 | # by g++ 2.96 with STABS debugging info. Here's what's going on, as | |
29 | # best as I can tell. | |
30 | # | |
31 | # The definition of `struct A' in `hang.H' refers to `struct B' as an | |
32 | # incomplete type. The stabs declare type number (1,3) to be a cross- | |
33 | # reference type, `xsB:'. | |
34 | # | |
35 | # The definition of `struct C' contains a nested definition for | |
36 | # `struct B' --- or more properly, `struct C::B'. However, the stabs | |
37 | # fail to qualify the structure tag: it just looks like a definition | |
38 | # for `struct B'. I think this is a compiler bug, but perhaps GCC | |
39 | # doesn't emit qualified names for a reason. | |
40 | # | |
41 | # `hang.H' gets #included by both `hang1.C' and `hang2.C'. So the | |
42 | # stabs for `struct A', the incomplete `struct B', and `struct C' | |
43 | # appear in both hang1.o's and hang2.o's stabs. | |
44 | # | |
45 | # When those two files are linked together, since hang2.o appears | |
46 | # later in the command line, its #inclusion of `hang.H' gets replaced | |
47 | # with an N_EXCL stab, referring back to hang1.o's stabs for the | |
48 | # header file. | |
49 | # | |
50 | # When GDB builds psymtabs for the executable hang, it notes that | |
51 | # hang2.o's stabs contain an N_EXCL referring to a header that appears | |
52 | # in full in hang1.o's stabs. So hang2.o's psymtab lists a dependency | |
53 | # on hang1.o's psymtab. | |
54 | # | |
55 | # When the user types the command `print var_in_b', GDB scans the | |
56 | # psymtabs for a symbol by that name, and decides to read full symbols | |
57 | # for `hang2.o'. | |
58 | # | |
59 | # Since `hang2.o''s psymtab lists `hang1.o' as a dependency, GDB first | |
60 | # reads `hang1.o''s symbols. When GDB sees `(1,3)=xsB:', it creates a | |
61 | # type object for `struct B', sets its TYPE_FLAG_STUB flag, and | |
62 | # records it as type number `(1,3)'. | |
63 | # | |
64 | # When GDB finds the definition of `struct C::B', since the stabs | |
65 | # don't indicate that the type is nested within C, it treats it as | |
66 | # a definition of `struct B'. | |
67 | # | |
68 | # When GDB is finished reading `hang1.o''s symbols, it calls | |
69 | # `cleanup_undefined_types'. This function mistakes the definition of | |
70 | # `struct C::B' for a definition for `struct B', and overwrites the | |
71 | # incomplete type object for the real `struct B', using `memcpy'. Now | |
72 | # stabs type number `(1,3)' refers to this (incorrect) complete type. | |
73 | # Furthermore, the `memcpy' simply copies the original's `cv_type' | |
74 | # field to the target, giving the target a corrupt `cv_type' ring: the | |
75 | # chain does not point back to the target type. | |
76 | # | |
77 | # Having satisfied `hang2.o''s psymtab's dependencies, GDB begins to | |
78 | # read `hang2.o''s symbols. These contain the true definition for | |
79 | # `struct B', which refers to type number `(1,3)' as the type it's | |
80 | # defining. GDB looks up type `(1,3)', and finds the (incorrect) | |
81 | # complete type established by the call to `cleanup_undefined_types' | |
82 | # above. However, it doesn't notice that the type is already defined, | |
83 | # and passes it to `read_struct_type', which then writes the new | |
84 | # definition's size, field list, etc. into the type object which | |
85 | # already has those fields initialized. Adding insult to injury, | |
86 | # `read_struct_type' then calls `finish_cv_type'; since the `memcpy' | |
87 | # in `cleanup_undefined_types' corrupted the target type's `cv_type' | |
88 | # ring, `finish_cv_type' enters an infinite loop. | |
89 | ||
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90 | # This checks that GDB recognizes when a structure is about to be |
91 | # overwritten, and refuses, with a complaint. | |
92 | gdb_test "print var_in_b" " = 1729" "doesn't overwrite struct type" | |
93 | ||
94 | # This checks that cleanup_undefined_types doesn't create corrupt | |
95 | # cv_type chains. Note that var_in_hang3 does need to be declared in | |
96 | # a separate compilation unit, whose psymtab depends on hang1.o's | |
97 | # psymtab. Otherwise, GDB won't call cleanup_undefined_types (as it | |
98 | # finishes hang1.o's symbols) before it calls make_cv_type (while | |
99 | # reading hang3.o's symbols). | |
100 | # | |
101 | # The bug only happens when you compile with -gstabs+; Otherwise, GCC | |
102 | # won't include the `const' qualifier on `const_B_ptr' in `hang3.o''s | |
103 | # STABS, so GDB won't try to create a const variant of the smashed | |
104 | # struct type, and get caught by the corrupted cv_type chain. | |
105 | gdb_test "print var_in_hang3" " = 42" "doesn't corrupt cv_type chain" |