1#   Copyright 2002, 2004 Free Software Foundation, Inc.
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
5# the Free Software Foundation; either version 2 of the License, or
6# (at your option) any later version.
7#
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.
12#
13# You should have received a copy of the GNU General Public License
14# along with this program; if not, write to the Free Software
15# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
16
17if $tracelevel then {
18	strace $tracelevel
19}
20
21set prms_id 0
22set bug_id 0
23
24if { [skip_cplus_tests] } { continue }
25
26set testfile hang
27set binfile ${objdir}/${subdir}/${testfile}
28
29foreach file {hang1 hang2 hang3} {
30    if {[gdb_compile "${srcdir}/${subdir}/${file}.C" "${file}.o" object {c++ debug}] != ""} {
31        gdb_suppress_entire_file "Testcase compile failed, so all tests in this file will automatically fail."
32    }
33}
34
35if {[gdb_compile "hang1.o hang2.o hang3.o" ${binfile} executable {c++ debug}] != "" } {
36     gdb_suppress_entire_file "Testcase compile failed, so all tests in this file will automatically fail."
37}
38
39
40gdb_exit
41gdb_start
42gdb_reinitialize_dir $srcdir/$subdir
43gdb_load ${binfile}
44
45
46# As of May 1, 2002, GDB hangs trying to read the debug info for the
47# `hang2.o' compilation unit from the executable `hang', when compiled
48# by g++ 2.96 with STABS debugging info.  Here's what's going on, as
49# best as I can tell.
50#
51# The definition of `struct A' in `hang.H' refers to `struct B' as an
52# incomplete type.  The stabs declare type number (1,3) to be a cross-
53# reference type, `xsB:'.
54#
55# The definition of `struct C' contains a nested definition for
56# `struct B' --- or more properly, `struct C::B'.  However, the stabs
57# fail to qualify the structure tag: it just looks like a definition
58# for `struct B'.  I think this is a compiler bug, but perhaps GCC
59# doesn't emit qualified names for a reason.
60#
61# `hang.H' gets #included by both `hang1.C' and `hang2.C'.  So the
62# stabs for `struct A', the incomplete `struct B', and `struct C'
63# appear in both hang1.o's and hang2.o's stabs.
64#
65# When those two files are linked together, since hang2.o appears
66# later in the command line, its #inclusion of `hang.H' gets replaced
67# with an N_EXCL stab, referring back to hang1.o's stabs for the
68# header file.
69#
70# When GDB builds psymtabs for the executable hang, it notes that
71# hang2.o's stabs contain an N_EXCL referring to a header that appears
72# in full in hang1.o's stabs.  So hang2.o's psymtab lists a dependency
73# on hang1.o's psymtab.
74#
75# When the user types the command `print var_in_b', GDB scans the
76# psymtabs for a symbol by that name, and decides to read full symbols
77# for `hang2.o'.
78#
79# Since `hang2.o''s psymtab lists `hang1.o' as a dependency, GDB first
80# reads `hang1.o''s symbols.  When GDB sees `(1,3)=xsB:', it creates a
81# type object for `struct B', sets its TYPE_FLAG_STUB flag, and
82# records it as type number `(1,3)'.
83#
84# When GDB finds the definition of `struct C::B', since the stabs
85# don't indicate that the type is nested within C, it treats it as
86# a definition of `struct B'.
87#
88# When GDB is finished reading `hang1.o''s symbols, it calls
89# `cleanup_undefined_types'.  This function mistakes the definition of
90# `struct C::B' for a definition for `struct B', and overwrites the
91# incomplete type object for the real `struct B', using `memcpy'.  Now
92# stabs type number `(1,3)' refers to this (incorrect) complete type.
93# Furthermore, the `memcpy' simply copies the original's `cv_type'
94# field to the target, giving the target a corrupt `cv_type' ring: the
95# chain does not point back to the target type.
96#
97# Having satisfied `hang2.o''s psymtab's dependencies, GDB begins to
98# read `hang2.o''s symbols.  These contain the true definition for
99# `struct B', which refers to type number `(1,3)' as the type it's
100# defining.  GDB looks up type `(1,3)', and finds the (incorrect)
101# complete type established by the call to `cleanup_undefined_types'
102# above.  However, it doesn't notice that the type is already defined,
103# and passes it to `read_struct_type', which then writes the new
104# definition's size, field list, etc. into the type object which
105# already has those fields initialized.  Adding insult to injury,
106# `read_struct_type' then calls `finish_cv_type'; since the `memcpy'
107# in `cleanup_undefined_types' corrupted the target type's `cv_type'
108# ring, `finish_cv_type' enters an infinite loop.
109
110# This checks that GDB recognizes when a structure is about to be
111# overwritten, and refuses, with a complaint.
112gdb_test "print var_in_b" " = 1729" "doesn't overwrite struct type"
113
114# This checks that cleanup_undefined_types doesn't create corrupt
115# cv_type chains.  Note that var_in_hang3 does need to be declared in
116# a separate compilation unit, whose psymtab depends on hang1.o's
117# psymtab.  Otherwise, GDB won't call cleanup_undefined_types (as it
118# finishes hang1.o's symbols) before it calls make_cv_type (while
119# reading hang3.o's symbols).
120#
121# The bug only happens when you compile with -gstabs+; Otherwise, GCC
122# won't include the `const' qualifier on `const_B_ptr' in `hang3.o''s
123# STABS, so GDB won't try to create a const variant of the smashed
124# struct type, and get caught by the corrupted cv_type chain.
125gdb_test "print var_in_hang3" " = 42" "doesn't corrupt cv_type chain"
126