RE: [PATCH 1/1] gdb: Fix arrays of variable length strings for FORTRAN

["Ijaz, Abdul B" <abdul.b.ijaz@intel.com>]

Thanks Andrew for the feedback.

> You should definitely mention this in the commit message I think, ideally, just mention which test showed the regression and why (e.g. printing a Fortran variable while the language is forced to C).

Sure Will do.

> I noticed you dropped `resolve_p` from the end of the argument list here.  Is this intentional?

Thanks for pointing it out. No it was not intentional, I think change introduce while fixing conflicts. Will revert it. 

> I think we should do _something_ with the stride, given how closely related arrays and strings seem to be, maybe just this would do:

>  prop = type->dyn_prop (DYN_PROP_BYTE_STRIDE);
>  if (prop != nullptr && type->code () == TYPE_CODE_STRING)
>    {
>      prop = nullptr;
>      warning (_("byte stride property ignored on string type"));
>    }

Will add it and will hopefully try to test and then push the changes for review today.

Thanks & Best Regards,
Abdul Basit

-----Original Message-----
From: Andrew Burgess <andrew.burgess@embecosm.com> 
Sent: Wednesday, August 25, 2021 10:37 AM
To: Ijaz, Abdul B <abdul.b.ijaz@intel.com>
Cc: abdul.b.ijaz <abijaz@ecsmtp.iul.intel.com>; gdb-patches@sourceware.org
Subject: Re: [PATCH 1/1] gdb: Fix arrays of variable length strings for FORTRAN

* Ijaz, Abdul B <abdul.b.ijaz@intel.com> [2021-08-23 08:47:46 +0000]:

> > GDB is not able to print arrays of FORTRAN variable length strings 
> > when dwarf info contains DW_AT_string_length only regarding the 
> > string length information.  So handing of dynamic array is updated 
> > to handle such cases.
> 
> Thanks for working on this.  I have some feedback, see below...
> >> Thanks Andrew for the feedback. I added my response below. Can you please review if it looks fine to you so I will update it accordingly. 
> 
> > 
> > Suppose we have
> > 
> > subroutine vla_array (arr1, arr2)
> >   character (len=*):: arr1 (:)
> >   character (len=5):: arr2 (:)
> > 
> >   print *, arr1 ! break-here
> >   print *, arr2
> > end subroutine vla_array
> > 
> > The "print arr1" and "print arr2" command at the "break-here" line 
> > gives the following output:
> > 
> > (gdb) print arr1
> > $1 = (<error reading variable>
> > (gdb) print arr2
> > $2 = ('abcde', 'abcde', 'abcde')
> > (gdb) ptype arr1
> > type = character*(*) (5)
> > (gdb) ptype arr2
> > type = character*5 (3)
> > 
> > So GDB is able to print the array of string with static length but 
> > for variable length it fail to do so.  For this case now improve 
> > handling of the TYPE_CODE_STRING code in dynamic array length 
> > resolving function to set the static length of strings as well when 
> > only DW_AT_string_length is given in the dwarf info.
> > 
> > Dwarf info using Intel® Fortran Compiler for such case contains following:
> >  <1><fd>: Abbrev Number: 12 (DW_TAG_string_type)
> >     <fe>   DW_AT_name        : (indirect string, offset: 0xd2): .str.ARR1
> >     <102>   DW_AT_string_length: 3 byte block: 97 23 8 	(DW_OP_push_object_address; DW_OP_plus_uconst: 8)
> 
> I don't think the extra indentation before "DW_AT_string_length" is correct here, this attribute is a child of the DW_TAG_string_type, right?  Not a child of the DW_AT_name.
> 
> >> This is output of readelf also there is no extra indentation before 
> >> "DW_AT_string_length". DW_AT_name has 2 digits in front <fe> while 
> >> DW_AT_string_lengt has 3 "<102>" so this is 1 more to right. Yes 
> >> "DW_AT_string_length" is a child of the DW_TAG_string_type.

Ah, OK that makes sense.  No need to change anything then.

> 
> 
> > 
> > After fixing it and compiling using Intel® Fortran Compiler now gdb 
> > shows
> > following:
> > 
> > (gdb) p arr1
> > $1 = ('abddefghij', 'abddefghij', 'abddefghij', 'abddefghij',
> > 'abddefghij')
> > (gdb) p arr2
> > $2 = ('abcde', 'abcde', 'abcde')
> > (gdb) ptype arr1
> > type = character*10 (5)
> > (gdb) ptype arr2
> > type = character*5 (3)
> > 
> > gdb/ChangeLog:
> > 2021-08-20  Abdul Basit Ijaz  <abdul.b.ijaz@intel.com>
> > 
> > 	* gdbtypes.c (resolve_dynamic_array_or_string): Improve handling
> > 	of TYPE_CODE_STRING code to use return value of create_string_type
> > 	outcome for this case.
> > 	* c-valprint.c (c_value_print_inner): Handle String type code
> > 	in the same way as the Array type code.
> > 
> > gdb/testsuite/ChangeLog:
> > 2021-08-20  Abdul Basit Ijaz  <abdul.b.ijaz@intel.com>
> > 
> > 	* gdb.fortran/vla-array.f90: New fie.
> > 	* gdb.fortran/vla-array.exp: New fie.
> > 
> > 2021-08-20 Abdul Basit Ijaz <abdul.b.ijaz@intel.com>
> > ---
> >  gdb/c-valprint.c                        |  1 +
> >  gdb/gdbtypes.c                          | 12 ++++--
> >  gdb/testsuite/gdb.fortran/vla-array.exp | 57
> > +++++++++++++++++++++++++
> >  gdb/testsuite/gdb.fortran/vla-array.f90 | 44 +++++++++++++++++++
> >  4 files changed, 110 insertions(+), 4 deletions(-)  create mode
> > 100644 gdb/testsuite/gdb.fortran/vla-array.exp
> >  create mode 100644 gdb/testsuite/gdb.fortran/vla-array.f90
> > 
> > diff --git a/gdb/c-valprint.c b/gdb/c-valprint.c index
> > 9c82869525f..e5a8e122676 100644
> > --- a/gdb/c-valprint.c
> > +++ b/gdb/c-valprint.c
> > @@ -426,6 +426,7 @@ c_value_print_inner (struct value *val, struct ui_file *stream, int recurse,
> >    switch (type->code ())
> >      {
> >      case TYPE_CODE_ARRAY:
> > +    case TYPE_CODE_STRING:
> >        c_value_print_array (val, stream, recurse, options);
> >        break;
> 
> I don't understand what part this change plays in this patch.  I can see below how you're now creating values with TYPE_CODE_STRING instead of TYPE_CODE_ARRAY, but then I'd expect these to be covered by the existing handling of TYPE_CODE_STRING in f_language::value_print_inner.
> 
> Of course, if you forced the language to C while inside the Fortran frame and tried to print the string value then I guess maybe you'd hit this case, but I don't think your test does this, and if that is the case you're covering here it might be worth splitting this into a separate commit to make the split crystal clear.
> 
> >> Actually this part was only modified since after fixig the issue 
> >> test "gdb.fortran/mixed-lang-stack.exp" has shown regression for 
> >> exactly the same scenario you mentioned "forced the language to C 
> >> while inside the Fortran frame" so that is why it was updated in 
> >> the same patch and this change is cover by this test 
> >> "gdb.fortran/mixed-lang-stack.exp" already.  So please let me know 
> >> shall we move it to separate patch.

You should definitely mention this in the commit message I think, ideally, just mention which test showed the regression and why (e.g. printing a Fortran variable while the language is forced to C).

> 
> 
> 
> >  
> > diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c index 
> > 74ad5d6f7fe..1444c5feb6c 100644
> > --- a/gdb/gdbtypes.c
> > +++ b/gdb/gdbtypes.c
> > @@ -2312,8 +2312,9 @@ resolve_dynamic_array_or_string (struct type *type,
> >    range_type = resolve_dynamic_range (range_type, addr_stack, 
> > resolve_p);
> >  
> >    ary_dim = check_typedef (TYPE_TARGET_TYPE (type));
> > -  if (ary_dim != NULL && ary_dim->code () == TYPE_CODE_ARRAY)
> > -    elt_type = resolve_dynamic_array_or_string (ary_dim, addr_stack, resolve_p);
> > +  if (ary_dim != NULL && (ary_dim->code () == TYPE_CODE_ARRAY
> > +      || ary_dim->code () == TYPE_CODE_STRING))
> 
> >> Will update the indentation like you pointed out in second email.
> 
> 
> > +    elt_type = resolve_dynamic_array_or_string (ary_dim, 
> > + addr_stack);

I noticed you dropped `resolve_p` from the end of the argument list here.  Is this intentional?

> >    else
> >      elt_type = TYPE_TARGET_TYPE (type);
> >  
> > @@ -2337,8 +2338,11 @@ resolve_dynamic_array_or_string (struct type *type,
> >    else
> >      bit_stride = TYPE_FIELD_BITSIZE (type, 0);
> >  
> > -  return create_array_type_with_stride (type, elt_type, range_type, NULL,
> > -					bit_stride);
> > +  if (type->code () == TYPE_CODE_STRING)
> > +    return create_string_type (type, elt_type, range_type);
> 
> I wonder if we should be doing anything with the bit_stride here?  I'm not sure if it makes sense for the bit_stride to be anything other than zero, but at the very least it feels like we should throw an error if the stride is not zero ....
> 
> >> Regarding bit_stride it is not needed for string type.  So shall we 
> >> can put a check to try reading it only for array type only since it 
> >> will not be needed for string type instead of throwing error.

I think we should do _something_ with the stride, given how closely related arrays and strings seem to be, maybe just this would do:

  prop = type->dyn_prop (DYN_PROP_BYTE_STRIDE);
  if (prop != nullptr && type->code () == TYPE_CODE_STRING)
    {
      prop = nullptr;
      warning (_("byte stride property ignored on string type"));
    }

if this ever does crop up we can figure out what's going on then.

Thanks,
Andrew

> 
> 
> > +  else
> > +    return create_array_type_with_stride (type, elt_type, range_type, NULL,
> > +                                        bit_stride);
> >  }
> >  
> >  /* Resolve dynamic bounds of members of the union TYPE to static 
> > diff --git a/gdb/testsuite/gdb.fortran/vla-array.exp
> > b/gdb/testsuite/gdb.fortran/vla-array.exp
> > new file mode 100644
> > index 00000000000..a9223576bbd
> > --- /dev/null
> > +++ b/gdb/testsuite/gdb.fortran/vla-array.exp
> > @@ -0,0 +1,57 @@
> > +# Copyright 2021 Free Software Foundation, Inc.
> > +
> > +# This program is free software; you can redistribute it and/or 
> > +modify # it under the terms of the GNU General Public License as 
> > +published by # the Free Software Foundation; either version 3 of 
> > +the License, or # (at your option) any later version.
> > +#
> > +# This program is distributed in the hope that it will be useful, # 
> > +but WITHOUT ANY WARRANTY; without even the implied warranty of # 
> > +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the # GNU 
> > +General Public License for more details.
> > +#
> > +# You should have received a copy of the GNU General Public License 
> > +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
> > +
> > +standard_testfile ".f90"
> > +load_lib "fortran.exp"
> > +
> > +if {[skip_fortran_tests]} { return -1 }
> > +
> > +if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile} \
> > +     {debug f90 quiet}] } {
> > +    return -1
> > +}
> > +
> > +if ![fortran_runto_main] {
> > +    untested "could not run to main"
> > +    return -1
> > +}
> > +
> > +# Try to access vla string / vla string array / string array values
> 
> Full stop at the end of the comment.
> >> Will do
> 
> Thanks & Best Regards,
> Abdul Basit
> 
> 
> > +gdb_breakpoint [gdb_get_line_number "arr_vla1-print"] 
> > +gdb_continue_to_breakpoint "arr_vla1-print"
> > +
> > +# GFortran does not emit DW_TAG_string_type for array of variable 
> > +length # string.
> > +if [test_compiler_info "gcc*"] { setup_xfail *-*-* gcc/101826 } 
> > +gdb_test "print arr_vla1"  \
> > +    " = \\\('vlaaryvlaary', 'vlaaryvlaary', 'vlaaryvlaary', 'vlaaryvlaary', 'vlaaryvlaary'\\\)"  \
> > +    "print vla string array"
> > +
> > +if [test_compiler_info "gcc*"] { setup_xfail *-*-* gcc/101826 } 
> > +gdb_test "ptype arr_vla1"  \
> > +    "type = character\\*12 \\(5\\)"  \
> > +    "print variable length string array type"
> > +gdb_test "print arr_vla2"  \
> > +    " = 'vlaary'"  \
> > +    "print variable length string"
> > +gdb_test "ptype arr_vla2"  \
> > +    "type = character\\*6"  \
> > +    "print variable length string type"
> > +gdb_test "print arr2"  \
> > +    " = \\\('vlaaryvla', 'vlaaryvla', 'vlaaryvla'\\\)"  \
> > +    "print string array"
> > +gdb_test "ptype arr2"  \
> > +    "type = character\\*9 \\(3\\)"  \
> > +    "print string array type"
> > diff --git a/gdb/testsuite/gdb.fortran/vla-array.f90
> > b/gdb/testsuite/gdb.fortran/vla-array.f90
> > new file mode 100644
> > index 00000000000..612e84fe213
> > --- /dev/null
> > +++ b/gdb/testsuite/gdb.fortran/vla-array.f90
> > @@ -0,0 +1,44 @@
> > +! Copyright 2021 Free Software Foundation, Inc.
> > +!
> > +! This program is free software; you can redistribute it and/or 
> > +modify ! it under the terms of the GNU General Public License as 
> > +published by ! the Free Software Foundation; either version 3 of 
> > +the License, or ! (at your option) any later version.
> > +!
> > +! This program is distributed in the hope that it will be useful, ! 
> > +but WITHOUT ANY WARRANTY; without even the implied warranty of ! 
> > +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the ! GNU 
> > +General Public License for more details.
> > +!
> > +! You should have received a copy of the GNU General Public License ! 
> > +along with this program.  If not, see <http://www.gnu.org/licenses/>.
> > +
> > +subroutine vla_array_func (arr_vla1, arr_vla2, arr2)
> > +  character (len=*):: arr_vla1 (:)
> > +  character (len=*):: arr_vla2
> > +  character (len=9):: arr2 (:)
> > +
> > +  print *, arr_vla1    ! arr_vla1-print
> > +  print *, arr_vla2
> > +  print *, arr2
> > +end subroutine vla_array_func
> > +
> > +program vla_array_main
> > +interface
> > +  subroutine vla_array_func (arr_vla1, arr_vla2, arr2)
> > +    character (len=*):: arr_vla1 (:)
> > +    character (len=*):: arr_vla2
> > +    character (len=9):: arr2 (:)
> > +  end subroutine vla_array_func
> > +end interface
> > +  character (len=9) :: arr1 (3)
> > +  character (len=6) :: arr2
> > +  character (len=12) :: arr3 (5)
> > +
> > +  arr1 = 'vlaaryvla'
> > +  arr2 = 'vlaary'
> > +  arr3 = 'vlaaryvlaary'
> > +
> > +  call vla_array_func (arr3, arr2, arr1)
> > +
> > +end program vla_array_main
> > --
> > 2.31.1
> >
>  
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Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
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Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928