[Bug debug/40040] New: gfortran invalid DW_AT_location for overridable variables

["jan dot kratochvil at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>]

Variables in Fortran modules compiled in -fPIC shared libraries will get unique
address by a copy relocation to the main executable.  Still .debug_info of the
library contains absolute DW_AT_location of the variable - without any
indirection through the GOT vector.

Debugger will then print the variable location not in active use.  Current FSF
GDB cannot resolve these variables but it was found by a new patch for modules:
http://sourceware.org/gdb/wiki/ArcherBranchManagement
archer-jankratochvil-fortran-module

Assuming no DW_AT_location should exist for such variables.  DW_AT_declaration
should be present there as such variables are NOT optimized-out.  Or
DW_AT_location using DW_FORM_block* indirecting GOT could be present?

For C the problem does not happen with GCC as it will put there _two_ DIEs and
the first one is just a declaration.  Current FSF GDB ignores any non-first
DIEs for a named object.  Still the second invalid DIE is redundant + invalid
even in the C case.

GNU Fortran (GCC) 4.4.0 20090427 (Red Hat 4.4.0-3)
GNU Fortran (GCC) 4.5.0 20090501 (experimental)

------------------------------------------------------------------------------

cat >lib.f90 <<EOH
module lib
        integer :: var = 1
end module lib
EOH
cat >main.f90 <<EOH
        use lib
        if (var .ne. 1) call abort
end
EOH
F="gfortran -Wall -g"; $F -o lib.so -shared -fPIC lib.f90; $F -o main main.f90
./lib.so

$ nm -D lib.so | grep var
0000000000200798 D __lib_MOD_var
$ nm -D main | grep var
0000000000600c38 B __lib_MOD_var

$ readelf -a lib.so | approx-grep var
Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [21] .data             PROGBITS         0000000000200798  00000798
       0000000000000004  0000000000000000  WA       0     0     4
Symbol table '.dynsym' contains 11 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     9: 0000000000200798     4 OBJECT  GLOBAL DEFAULT   21 __lib_MOD_var
Symbol table '.symtab' contains 57 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
    50: 0000000000200798     4 OBJECT  GLOBAL DEFAULT   21 __lib_MOD_var

$ readelf -a main | approx-grep var
Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [25] .bss              NOBITS           0000000000600c38  00000c34
       0000000000000018  0000000000000000  WA       0     0     8
Relocation section '.rela.dyn' at offset 0x560 contains 2 entries:
  Offset          Info           Type           Sym. Value    Sym. Name +
Addend
000000600c38  000c00000005 R_X86_64_COPY     0000000000600c38 __lib_MOD_var + 0
Symbol table '.dynsym' contains 14 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
    12: 0000000000600c38     4 OBJECT  GLOBAL DEFAULT   25 __lib_MOD_var
Symbol table '.symtab' contains 77 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
    59: 0000000000600c38     4 OBJECT  GLOBAL DEFAULT   25 __lib_MOD_var

$ readelf -wi lib.so | approx-grep var
 <1><2d>: Abbrev Number: 2 (DW_TAG_module)
    <2e>   DW_AT_name        : lib
 <2><38>: Abbrev Number: 3 (DW_TAG_variable)
    <39>   DW_AT_name        : var
    <3f>   DW_AT_type        : <0x4f>
    <43>   DW_AT_external    : 1
    <44>   DW_AT_location    : 9 byte block: 3 98 7 20 0 0 0 0 0       
(DW_OP_addr: 200798)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ invalid DW_AT_location

$ readelf -wi main | approx-grep var
 <1><2d>: Abbrev Number: 2 (DW_TAG_subprogram)
    <2f>   DW_AT_name        : (indirect string, offset: 0x9): MAIN__
 <2><50>: Abbrev Number: 4 (DW_TAG_imported_module)
    <53>   DW_AT_import      : <0x58>   [Abbrev Number: 5 (DW_TAG_module)]
 <1><58>: Abbrev Number: 5 (DW_TAG_module)
    <59>   DW_AT_name        : lib
    <5d>   DW_AT_declaration : 1


cat >clib.c <<EOH
int var = 1;

int
func (void)
{
  return var;
}
EOH
cat >cmain.c <<EOH
extern int var;

extern int func (void);

int
main (void)
{
  var = 2;
  return var == func () ? 0 : 1;
}
EOH
C="gcc -Wall -g"; $C -o clib.so -shared -fPIC clib.c; $C -o cmain cmain.c
./clib.so

$ nm -D clib.so | grep var
0000000000200800 D var
$ nm -D cmain | grep var
00000000006009c0 B var

$ readelf -wi clib.so | approx-grep var
 <1><55>: Abbrev Number: 4 (DW_TAG_variable)
    <56>   DW_AT_name        : var
    <5c>   DW_AT_type        : <0x4e>
    <60>   DW_AT_external    : 1
    <61>   DW_AT_declaration : 1
 <1><62>: Abbrev Number: 5 (DW_TAG_variable)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ redundant+invalid DIE
    <63>   DW_AT_name        : var
    <69>   DW_AT_type        : <0x4e>
    <6d>   DW_AT_external    : 1
    <6e>   DW_AT_location    : 9 byte block: 3 0 8 20 0 0 0 0 0        
(DW_OP_addr: 200800)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ invalid DW_AT_location


-- 
           Summary: gfortran invalid DW_AT_location for overridable
                    variables
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jan dot kratochvil at redhat dot com
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40040