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106 lines
4.9 KiB
Plaintext
106 lines
4.9 KiB
Plaintext
# Copyright 2002-2018 Free Software Foundation, Inc.
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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if { [skip_cplus_tests] } { continue }
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standard_testfile hang1.cc hang2.cc hang3.cc
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if {[prepare_for_testing "failed to prepare" $testfile \
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[list $srcfile $srcfile2 $srcfile3] {debug c++}]} {
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return -1
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}
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# As of May 1, 2002, GDB hangs trying to read the debug info for the
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# `hang2.o' compilation unit from the executable `hang', when compiled
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# by g++ 2.96 with STABS debugging info. Here's what's going on, as
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# best as I can tell.
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#
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# The definition of `struct A' in `hang.H' refers to `struct B' as an
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# incomplete type. The stabs declare type number (1,3) to be a cross-
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# reference type, `xsB:'.
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#
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# The definition of `struct C' contains a nested definition for
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# `struct B' --- or more properly, `struct C::B'. However, the stabs
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# fail to qualify the structure tag: it just looks like a definition
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# for `struct B'. I think this is a compiler bug, but perhaps GCC
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# doesn't emit qualified names for a reason.
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#
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# `hang.H' gets #included by both `hang1.C' and `hang2.C'. So the
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# stabs for `struct A', the incomplete `struct B', and `struct C'
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# appear in both hang1.o's and hang2.o's stabs.
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#
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# When those two files are linked together, since hang2.o appears
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# later in the command line, its #inclusion of `hang.H' gets replaced
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# with an N_EXCL stab, referring back to hang1.o's stabs for the
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# header file.
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#
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# When GDB builds psymtabs for the executable hang, it notes that
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# hang2.o's stabs contain an N_EXCL referring to a header that appears
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# in full in hang1.o's stabs. So hang2.o's psymtab lists a dependency
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# on hang1.o's psymtab.
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#
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# When the user types the command `print var_in_b', GDB scans the
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# psymtabs for a symbol by that name, and decides to read full symbols
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# for `hang2.o'.
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#
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# Since `hang2.o''s psymtab lists `hang1.o' as a dependency, GDB first
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# reads `hang1.o''s symbols. When GDB sees `(1,3)=xsB:', it creates a
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# type object for `struct B', sets its TYPE_STUB flag, and records it
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# as type number `(1,3)'.
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#
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# When GDB finds the definition of `struct C::B', since the stabs
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# don't indicate that the type is nested within C, it treats it as
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# a definition of `struct B'.
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#
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# When GDB is finished reading `hang1.o''s symbols, it calls
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# `cleanup_undefined_types'. This function mistakes the definition of
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# `struct C::B' for a definition for `struct B', and overwrites the
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# incomplete type object for the real `struct B', using `memcpy'. Now
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# stabs type number `(1,3)' refers to this (incorrect) complete type.
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# Furthermore, the `memcpy' simply copies the original's `cv_type'
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# field to the target, giving the target a corrupt `cv_type' ring: the
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# chain does not point back to the target type.
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#
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# Having satisfied `hang2.o''s psymtab's dependencies, GDB begins to
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# read `hang2.o''s symbols. These contain the true definition for
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# `struct B', which refers to type number `(1,3)' as the type it's
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# defining. GDB looks up type `(1,3)', and finds the (incorrect)
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# complete type established by the call to `cleanup_undefined_types'
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# above. However, it doesn't notice that the type is already defined,
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# and passes it to `read_struct_type', which then writes the new
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# definition's size, field list, etc. into the type object which
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# already has those fields initialized. Adding insult to injury,
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# `read_struct_type' then calls `finish_cv_type'; since the `memcpy'
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# in `cleanup_undefined_types' corrupted the target type's `cv_type'
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# ring, `finish_cv_type' enters an infinite loop.
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# This checks that GDB recognizes when a structure is about to be
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# overwritten, and refuses, with a complaint.
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gdb_test "print var_in_b" " = 1729" "doesn't overwrite struct type"
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# This checks that cleanup_undefined_types doesn't create corrupt
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# cv_type chains. Note that var_in_hang3 does need to be declared in
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# a separate compilation unit, whose psymtab depends on hang1.o's
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# psymtab. Otherwise, GDB won't call cleanup_undefined_types (as it
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# finishes hang1.o's symbols) before it calls make_cv_type (while
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# reading hang3.o's symbols).
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#
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# The bug only happens when you compile with -gstabs+; Otherwise, GCC
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# won't include the `const' qualifier on `const_B_ptr' in `hang3.o''s
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# STABS, so GDB won't try to create a const variant of the smashed
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# struct type, and get caught by the corrupted cv_type chain.
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gdb_test "print var_in_hang3" " = 42" "doesn't corrupt cv_type chain"
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