[Bug c++/80596] New: g++ generates incomplete DWARF debug information for array-typedefs

[paul.kaletta at intel dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80596

            Bug ID: 80596
           Summary: g++ generates incomplete DWARF debug information for
                    array-typedefs
           Product: gcc
           Version: 6.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: paul.kaletta at intel dot com
  Target Milestone: ---

The following observations apply to g++ 6.1.0 and earlier.

Consider the following program:

typedef int T_ACCESS_TECHNOLOGY;
typedef T_ACCESS_TECHNOLOGY T_AT;
typedef T_AT T_AT_ARRAY[5];
T_AT_ARRAY t_at_array;

When compiled with gcc 6.1.0 (gcc -g -c sample.c -o sample_gcc.o), the
generated DWARF looks as follows:

< 1><0x0000001d GOFF=0x0000001d>    DW_TAG_typedef
    DW_AT_name                  T_ACCESS_TECHNOLOGY
    DW_AT_decl_file             0x00000001 /home/pkaletta/gcc_bug/sample.c
    DW_AT_decl_line             0x00000001
    DW_AT_type                  <0x00000028 GOFF=0x00000028>
< 1><0x00000028 GOFF=0x00000028>    DW_TAG_base_type
    DW_AT_byte_size             0x00000004
    DW_AT_encoding              DW_ATE_signed
    DW_AT_name                  int
< 1><0x0000002f GOFF=0x0000002f>    DW_TAG_typedef
    DW_AT_name                  T_AT
    DW_AT_decl_file             0x00000001 /home/pkaletta/gcc_bug/sample.c
    DW_AT_decl_line             0x00000002
    DW_AT_type                  <0x0000001d GOFF=0x0000001d>
< 1><0x0000003a GOFF=0x0000003a>    DW_TAG_typedef
    DW_AT_name                  T_AT_ARRAY
    DW_AT_decl_file             0x00000001 /home/pkaletta/gcc_bug/sample.c
    DW_AT_decl_line             0x00000003
    DW_AT_type                  <0x00000045 GOFF=0x00000045>
< 1><0x00000045 GOFF=0x00000045>    DW_TAG_array_type
    DW_AT_type                  <0x0000002f GOFF=0x0000002f>
    DW_AT_sibling               <0x00000055 GOFF=0x00000055>
< 2><0x0000004e GOFF=0x0000004e>      DW_TAG_subrange_type
      DW_AT_type                  <0x00000055 GOFF=0x00000055>
      DW_AT_upper_bound           4
< 1><0x00000055 GOFF=0x00000055>    DW_TAG_base_type
    DW_AT_byte_size             0x00000008
    DW_AT_encoding              DW_ATE_unsigned
    DW_AT_name                  sizetype
< 1><0x0000005c GOFF=0x0000005c>    DW_TAG_variable
    DW_AT_name                  t_at_array
    DW_AT_decl_file             0x00000001 /home/pkaletta/gcc_bug/sample.c
    DW_AT_decl_line             0x00000004
    DW_AT_type                  <0x0000003a GOFF=0x0000003a>
    DW_AT_external              yes(1)
    DW_AT_location              len 0x0009: 031000000000000000: DW_OP_addr
0x00000010


When compiled with g++ (g++ -g -c sample.c -o sample_g++.o):
< 1><0x0000001d GOFF=0x0000001d>    DW_TAG_base_type
    DW_AT_byte_size             0x00000004
    DW_AT_encoding              DW_ATE_signed
    DW_AT_name                  int
< 1><0x00000024 GOFF=0x00000024>    DW_TAG_typedef
    DW_AT_name                  T_AT_ARRAY
    DW_AT_decl_file             0x00000001 /home/pkaletta/gcc_bug/sample.c
    DW_AT_decl_line             0x00000003
< 1><0x0000002b GOFF=0x0000002b>    DW_TAG_base_type
    DW_AT_byte_size             0x00000008
    DW_AT_encoding              DW_ATE_unsigned
    DW_AT_name                  sizetype
< 1><0x00000032 GOFF=0x00000032>    DW_TAG_variable
    DW_AT_name                  t_at_array
    DW_AT_decl_file             0x00000001 /home/pkaletta/gcc_bug/sample.c
    DW_AT_decl_line             0x00000004
    DW_AT_type                  <0x00000024 GOFF=0x00000024>
    DW_AT_external              yes(1)
    DW_AT_location              len 0x0009: 030000000000000000: DW_OP_addr
0x00000000

The debug info for C++ contains no trace of T_AT or
T_ACCESS_TECHNOLOGY.  The typedef DIE generated for T_AT_ARRAY looks
bogus (typedef to void?).  For earlier versions of g++ T_AT_ARRAY at
least shows up as an array of 5 ints, but that does not seem right
either.

In my opinion g++ (for C++) should behave just like gcc (for C) does,
and emit the entire chain of typedefs.

In my specific scenario, I would like to run some scripts on all
instances of T_ACCESS_TECHNOLOGY which is only possible if the type
information is preserved in the debug info.

Currently I can do this for C programs, but not for C++ programs.

-fno-eliminate-unused-debug-types doesn't help, as g++ will emit the
extra types, but fails to interconnect them.