[Bug translator/29037] Systemtap unable to find struct bitfield members for gcc11 compiled code

["wcohen at redhat dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=29037

--- Comment #2 from William Cohen <wcohen at redhat dot com> ---
dwflpp.cxx:3470 has a check on DW_AT_data_member_location and only adds things
if there a DW_AT_data_member_location seems to be part of the problem. 
However, just adding an additional check for DW_AT_data_bit_offset there is not
sufficient. Before adding the DW_AT_data_bit_offset check get the following in
the -vvv output:

finding location for local 'a' near address 0x401170, module bias 0
get_cfa_ops @0x401170, module_start @0x400000
dwfl_module_dwarf_cfi failed: no error
got eh cfi bias: 0x0
found cfa, info: -1 [start: 0x7f2cd31f669d, end: 0x561b5f61cff0, nops: 1
chaining to identifier '$a' at fields_probes_f35.stp:2:16
semantic error: no location for field 'icsk_ca_state':no error: operator '->'
at fields_probes_f35.stp:2:18
   thrown from: dwflpp.cxx:3481
        source:   if (@defined($a->icsk_ca_state))

After adding the DW_AT_data_bit_offset check:

finding location for local 'a' near address 0x401170, module bias 0
get_cfa_ops @0x401170, module_start @0x400000
dwfl_module_dwarf_cfi failed: no error
got eh cfi bias: 0x0
found cfa, info: -1 [start: 0x770000007c, end: 0x5b0000006e, nops: 1
chaining to identifier '$a' at fields_probes_f35.stp:2:16
semantic error: dwarf_getlocation_addr failed at this address (pc: 0x401170)
[man error::dwarf]: identifier '$a' at fields_probes_f35.stp:2:16
        dwarf_error: not a location list value
        dieoffset: 0x95 from
/home/wcohen/research/profiling/systemtap_write/gcc11_bitfield/fields_f35
        function: f at
/home/wcohen/research/profiling/systemtap_write/gcc11_bitfield/fields.c:14:1
        <error getting alternative locations: not a location list value>
   thrown from: dwflpp.cxx:3266
        source:   if (@defined($a->icsk_ca_state))
                               ^
I did a quick check with gdb to see if it was able to extract the bit field
information member information on the field_f35 example that does not have the
DW_AT_data_member_location, and gdb was able to get the info, so this looks to
be limited to systemtap rather than a problem in the elfutils libraries.

The fedora debuginfo is also missing the DW_AT_byte_size, so should check to
see how/where that is being used.

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