gdb/testsuite/gdb.c++/hang.exp

   1 #   Copyright (C) 2002 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
  17 # Please email any bugs, comments, and/or additions to this file to:
  18 # bug-gdb@prep.ai.mit.edu
  19
  20 if $tracelevel then {
  21         strace $tracelevel
  22 }
  23
  24 set prms_id 0
  25 set bug_id 0
  26
  27 if { [skip_cplus_tests] } { continue }
  28
  29 set testfile hang
  30 set binfile ${objdir}/${subdir}/${testfile}
  31
  32 foreach file {hang1 hang2} {
  33     if  { [gdb_compile "${srcdir}/${subdir}/${file}.C" "${file}.o" object {debug c++}] != "" } {
  34         gdb_suppress_entire_file "Testcase compile failed, so all tests in this file will automatically fail."
  35     }
  36 }
  37
  38 if {[gdb_compile "hang1.o hang2.o" ${binfile} executable {debug c++}] != "" } {
  39      gdb_suppress_entire_file "Testcase compile failed, so all tests in this file will automatically fail."
  40 }
  41
  42
  43 gdb_exit
  44 gdb_start
  45 gdb_reinitialize_dir $srcdir/$subdir
  46 gdb_load ${binfile}
  47
  48
  49 # As of May 1, 2002, GDB hangs trying to read the debug info for the
  50 # `hang2.o' compilation unit from the executable `hang', when compiled
  51 # by g++ 2.96 with STABS debugging info.  Here's what's going on, as
  52 # best as I can tell.
  53 #
  54 # The definition of `struct A' in `hang.H' refers to `struct B' as an
  55 # incomplete type.  The stabs declare type number (1,3) to be a cross-
  56 # reference type, `xsB:'.
  57 #
  58 # The definition of `struct C' contains a nested definition for
  59 # `struct B' --- or more properly, `struct C::B'.  However, the stabs
  60 # fail to qualify the structure tag: it just looks like a definition
  61 # for `struct B'.  I think this is a compiler bug, but perhaps GCC
  62 # doesn't emit qualified names for a reason.
  63 #
  64 # `hang.H' gets #included by both `hang1.C' and `hang2.C'.  So the
  65 # stabs for `struct A', the incomplete `struct B', and `struct C'
  66 # appear in both hang1.o's and hang2.o's stabs.
  67 #
  68 # When those two files are linked together, since hang2.o appears
  69 # later in the command line, its #inclusion of `hang.H' gets replaced
  70 # with an N_EXCL stab, referring back to hang1.o's stabs for the
  71 # header file.
  72 #
  73 # When GDB builds psymtabs for the executable hang, it notes that
  74 # hang2.o's stabs contain an N_EXCL referring to a header that appears
  75 # in full in hang1.o's stabs.  So hang2.o's psymtab lists a dependency
  76 # on hang1.o's psymtab.
  77 #
  78 # When the user types the command `print var_in_b', GDB scans the
  79 # psymtabs for a symbol by that name, and decides to read full symbols
  80 # for `hang2.o'.
  81 #
  82 # Since `hang2.o''s psymtab lists `hang1.o' as a dependency, GDB first
  83 # reads `hang1.o''s symbols.  When GDB sees `(1,3)=xsB:', it creates a
  84 # type object for `struct B', sets its TYPE_FLAG_STUB flag, and
  85 # records it as type number `(1,3)'.
  86 #
  87 # When GDB finds the definition of `struct C::B', since the stabs
  88 # don't indicate that the type is nested within C, it treats it as
  89 # a definition of `struct B'.
  90 #
  91 # When GDB is finished reading `hang1.o''s symbols, it calls
  92 # `cleanup_undefined_types'.  This function mistakes the definition of
  93 # `struct C::B' for a definition for `struct B', and overwrites the
  94 # incomplete type object for the real `struct B', using `memcpy'.  Now
  95 # stabs type number `(1,3)' refers to this (incorrect) complete type.
  96 # Furthermore, the `memcpy' simply copies the original's `cv_type'
  97 # field to the target, giving the target a corrupt `cv_type' ring: the
  98 # chain does not point back to the target type.
  99 #
 100 # Having satisfied `hang2.o''s psymtab's dependencies, GDB begins to
 101 # read `hang2.o''s symbols.  These contain the true definition for
 102 # `struct B', which refers to type number `(1,3)' as the type it's
 103 # defining.  GDB looks up type `(1,3)', and finds the (incorrect)
 104 # complete type established by the call to `cleanup_undefined_types'
 105 # above.  However, it doesn't notice that the type is already defined,
 106 # and passes it to `read_struct_type', which then writes the new
 107 # definition's size, field list, etc. into the type object which
 108 # already has those fields initialized.  Adding insult to injury,
 109 # `read_struct_type' then calls `finish_cv_type'; since the `memcpy'
 110 # in `cleanup_undefined_types' corrupted the target type's `cv_type'
 111 # ring, `finish_cv_type' enters an infinite loop.
 112
 113 gdb_test "print var_in_b" " = 1729" "can read debug info"