--- /dev/null
+# Copyright (C) 2002 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 2 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, write to the Free Software
+# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+
+# Please email any bugs, comments, and/or additions to this file to:
+# bug-gdb@prep.ai.mit.edu
+
+if $tracelevel then {
+ strace $tracelevel
+}
+
+set prms_id 0
+set bug_id 0
+
+if { [skip_cplus_tests] } { continue }
+
+set testfile hang
+set binfile ${objdir}/${subdir}/${testfile}
+
+foreach file {hang1 hang2} {
+ if { [gdb_compile "${srcdir}/${subdir}/${file}.C" "${file}.o" object {debug c++}] != "" } {
+ gdb_suppress_entire_file "Testcase compile failed, so all tests in this file will automatically fail."
+ }
+}
+
+if {[gdb_compile "hang1.o hang2.o" ${binfile} executable {debug c++}] != "" } {
+ gdb_suppress_entire_file "Testcase compile failed, so all tests in this file will automatically fail."
+}
+
+
+gdb_exit
+gdb_start
+gdb_reinitialize_dir $srcdir/$subdir
+gdb_load ${binfile}
+
+
+# As of May 1, 2002, GDB hangs trying to read the debug info for the
+# `hang2.o' compilation unit from the executable `hang', when compiled
+# by g++ 2.96 with STABS debugging info. Here's what's going on, as
+# best as I can tell.
+#
+# The definition of `struct A' in `hang.H' refers to `struct B' as an
+# incomplete type. The stabs declare type number (1,3) to be a cross-
+# reference type, `xsB:'.
+#
+# The definition of `struct C' contains a nested definition for
+# `struct B' --- or more properly, `struct C::B'. However, the stabs
+# fail to qualify the structure tag: it just looks like a definition
+# for `struct B'. I think this is a compiler bug, but perhaps GCC
+# doesn't emit qualified names for a reason.
+#
+# `hang.H' gets #included by both `hang1.C' and `hang2.C'. So the
+# stabs for `struct A', the incomplete `struct B', and `struct C'
+# appear in both hang1.o's and hang2.o's stabs.
+#
+# When those two files are linked together, since hang2.o appears
+# later in the command line, its #inclusion of `hang.H' gets replaced
+# with an N_EXCL stab, referring back to hang1.o's stabs for the
+# header file.
+#
+# When GDB builds psymtabs for the executable hang, it notes that
+# hang2.o's stabs contain an N_EXCL referring to a header that appears
+# in full in hang1.o's stabs. So hang2.o's psymtab lists a dependency
+# on hang1.o's psymtab.
+#
+# When the user types the command `print var_in_b', GDB scans the
+# psymtabs for a symbol by that name, and decides to read full symbols
+# for `hang2.o'.
+#
+# Since `hang2.o''s psymtab lists `hang1.o' as a dependency, GDB first
+# reads `hang1.o''s symbols. When GDB sees `(1,3)=xsB:', it creates a
+# type object for `struct B', sets its TYPE_FLAG_STUB flag, and
+# records it as type number `(1,3)'.
+#
+# When GDB finds the definition of `struct C::B', since the stabs
+# don't indicate that the type is nested within C, it treats it as
+# a definition of `struct B'.
+#
+# When GDB is finished reading `hang1.o''s symbols, it calls
+# `cleanup_undefined_types'. This function mistakes the definition of
+# `struct C::B' for a definition for `struct B', and overwrites the
+# incomplete type object for the real `struct B', using `memcpy'. Now
+# stabs type number `(1,3)' refers to this (incorrect) complete type.
+# Furthermore, the `memcpy' simply copies the original's `cv_type'
+# field to the target, giving the target a corrupt `cv_type' ring: the
+# chain does not point back to the target type.
+#
+# Having satisfied `hang2.o''s psymtab's dependencies, GDB begins to
+# read `hang2.o''s symbols. These contain the true definition for
+# `struct B', which refers to type number `(1,3)' as the type it's
+# defining. GDB looks up type `(1,3)', and finds the (incorrect)
+# complete type established by the call to `cleanup_undefined_types'
+# above. However, it doesn't notice that the type is already defined,
+# and passes it to `read_struct_type', which then writes the new
+# definition's size, field list, etc. into the type object which
+# already has those fields initialized. Adding insult to injury,
+# `read_struct_type' then calls `finish_cv_type'; since the `memcpy'
+# in `cleanup_undefined_types' corrupted the target type's `cv_type'
+# ring, `finish_cv_type' enters an infinite loop.
+
+gdb_test "print var_in_b" " = 1729" "can read debug info"
projects / deliverable / binutils-gdb.git / commitdiff
