[Bug fortran/105272] New: Using entry inside module contained subroutines changes subroutine's scope in DWARF

[nils-christian.kempke at intel dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105272

            Bug ID: 105272
           Summary: Using entry inside module contained subroutines
                    changes subroutine's scope in DWARF
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nils-christian.kempke at intel dot com
  Target Milestone: ---

When compiling a subroutine inside a module like

  $ cat f_no_entry.f90
    module a
    contains
      subroutine b
        print *, "b"
      end subroutine b
    end module a

    program prog
      print *, "hi"
    end program prog
  $ gfortran -O0 -g ./f.f90
  $ gfortran --version
  GNU Fortran (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
  ...

the DWARF emitted shows that the DW_TAG_subprogram for subroutine b is a child
of the DW_TAG_module for a.  This seems reasonable and puts b into the scope of
a:

  $ objdump --dwarf=info ./a.out
  ...
   <1><a0>: Abbrev Number: 8 (DW_TAG_module)
      <a1>   DW_AT_name        : a
      <a3>   DW_AT_decl_file   : 1
      <a4>   DW_AT_decl_line   : 1
   <2><a5>: Abbrev Number: 9 (DW_TAG_subprogram)
      <a6>   DW_AT_external    : 1
      <a6>   DW_AT_name        : b
      <a8>   DW_AT_decl_file   : 1
      <a9>   DW_AT_decl_line   : 3
      <aa>   DW_AT_linkage_name: (indirect string, offset: 0x0): __a_MOD_b
      <ae>   DW_AT_low_pc      : 0x1179
      <b6>   DW_AT_high_pc     : 0x73
      <be>   DW_AT_frame_base  : 1 byte block: 9c        
(DW_OP_call_frame_cfa)
      <c0>   DW_AT_GNU_all_tail_call_sites: 1
   <2><c0>: Abbrev Number: 0
   <1><c1>: Abbrev Number: 0

Changing this example seemingly just a bit by adding an alternative entry point
to b via the 'entry' moves the subroutine (and the entry point) out of the
module and puts them into the scope of the whole compile unit TAG:

  $ cat f_entry.f90
  module a
  contains
    subroutine b
      entry bbb
      print *, "b"
    end subroutine b
  end module a

  program prog
    print *, "hi"
  end program prog
  $ gfortran -O0 -g ./f_entry.f90
  $ objdump --dwarf=info ./a.out
  ...
   <1><a0>: Abbrev Number: 8 (DW_TAG_module)
      <a1>   DW_AT_name        : a
      <a3>   DW_AT_decl_file   : 1
      <a4>   DW_AT_decl_line   : 1
      <a5>   DW_AT_sibling     : <0xd1>
   <2><a9>: Abbrev Number: 9 (DW_TAG_subprogram)
      <aa>   DW_AT_name        : (indirect string, offset: 0xa): master.0.b
      <ae>   DW_AT_decl_file   : 1
      <af>   DW_AT_decl_line   : 7
      <b0>   DW_AT_low_pc      : 0x1199
      <b8>   DW_AT_high_pc     : 0x8c
      <c0>   DW_AT_frame_base  : 1 byte block: 9c        
(DW_OP_call_frame_cfa)
      <c2>   DW_AT_GNU_all_tail_call_sites: 1
   <3><c2>: Abbrev Number: 10 (DW_TAG_formal_parameter)
      <c3>   DW_AT_name        : (indirect string, offset: 0x57): __entry
      <c7>   DW_AT_type        : <0xd8>
      <cb>   DW_AT_artificial  : 1
      <cb>   DW_AT_location    : 3 byte block: 91 d8 7b   (DW_OP_fbreg: -552)
   <3><cf>: Abbrev Number: 0
   <2><d0>: Abbrev Number: 0
  ...
   <1><d1>: Abbrev Number: 4 (DW_TAG_base_type)
      <d2>   DW_AT_byte_size   : 8
      <d3>   DW_AT_encoding    : 5        (signed)
      <d4>   DW_AT_name        : (indirect string, offset: 0x27):
integer(kind=8)
   <1><dd>: Abbrev Number: 11 (DW_TAG_subprogram)
      <de>   DW_AT_external    : 1
      <de>   DW_AT_name        : bbb
      <e2>   DW_AT_decl_file   : 1
      <e3>   DW_AT_decl_line   : 4
      <e4>   DW_AT_linkage_name: (indirect string, offset: 0x142): __a_MOD_bbb
      <e8>   DW_AT_low_pc      : 0x1189
      <f0>   DW_AT_high_pc     : 0x10
      <f8>   DW_AT_frame_base  : 1 byte block: 9c        
(DW_OP_call_frame_cfa)
      <fa>   DW_AT_GNU_all_tail_call_sites: 1
   <1><fa>: Abbrev Number: 11 (DW_TAG_subprogram)
      <fb>   DW_AT_external    : 1
      <fb>   DW_AT_name        : b
      <fd>   DW_AT_decl_file   : 1
      <fe>   DW_AT_decl_line   : 3
      <ff>   DW_AT_linkage_name: (indirect string, offset: 0x0): __a_MOD_b
      <103>   DW_AT_low_pc      : 0x1179
      <10b>   DW_AT_high_pc     : 0x10
      <113>   DW_AT_frame_base  : 1 byte block: 9c       
(DW_OP_call_frame_cfa)
      <115>   DW_AT_GNU_all_tail_call_sites: 1
   <1><115>: Abbrev Number: 0

This behavior seems odd. I stumbled upon this when trying to access the entry
point bbb in gdb via a::bbb (as bbb is in the module's scope) which I could
not.

There is a likely related issue about gfortran not emitting a
DW_TAG_entry_point for entry points
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=37134.