Re: [PATCH] Correctly print subrange types in generic_value_print

[Joel Brobecker <brobecker@adacore.com>]

Hi Tom,

On Thu, Mar 10, 2022 at 09:25:56AM -0700, Tom Tromey via Gdb-patches wrote:
> I noticed that generic_value_print assumes that a subrange type is
> always a subrange of an integer type.  However, this isn't necessarily
> the case.  In Ada, for example, one has subranges of character and
> enumeration types.
> 
> This code isn't often exercised, I think, because languages with real
> subrange types tend to implement their own printers.  However, it
> still seemed worth fixing.

Agreed. Thanks for the patch and the testcase, it looks good to me.

> ---
>  gdb/testsuite/gdb.dwarf2/subrange-enum.exp | 78 ++++++++++++++++++++++
>  gdb/valprint.c                             |  9 ++-
>  2 files changed, 86 insertions(+), 1 deletion(-)
>  create mode 100644 gdb/testsuite/gdb.dwarf2/subrange-enum.exp
> 
> diff --git a/gdb/testsuite/gdb.dwarf2/subrange-enum.exp b/gdb/testsuite/gdb.dwarf2/subrange-enum.exp
> new file mode 100644
> index 00000000000..b9f7cb68233
> --- /dev/null
> +++ b/gdb/testsuite/gdb.dwarf2/subrange-enum.exp
> @@ -0,0 +1,78 @@
> +# Copyright 2022 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/>.
> +
> +# Test generic printing of subrange values.
> +
> +load_lib dwarf.exp
> +
> +# This test can only be run on targets which support DWARF-2 and use gas.
> +if {![dwarf2_support]} {
> +    return 0
> +}
> +
> +standard_testfile main.c -dw.S
> +
> +# Make some DWARF for the test.
> +set asm_file [standard_output_file $srcfile2]
> +Dwarf::assemble $asm_file {
> +    cu {} {
> +	compile_unit {{language @DW_LANG_C}} {
> +	    declare_labels integer_label enum_label subrange_label
> +
> +            integer_label: DW_TAG_base_type {
> +                {DW_AT_byte_size 4 DW_FORM_sdata}
> +                {DW_AT_encoding  @DW_ATE_signed}
> +                {DW_AT_name      integer}
> +            }
> +
> +	    enum_label: DW_TAG_enumeration_type {
> +		{DW_AT_name E}
> +		{DW_AT_type :$integer_label}
> +	    } {
> +		DW_TAG_enumerator {
> +		    {DW_AT_name ONE}
> +		    {DW_AT_const_value 1 DW_FORM_sdata}
> +		}
> +		DW_TAG_enumerator {
> +		    {DW_AT_name TWO}
> +		    {DW_AT_const_value 2 DW_FORM_sdata}
> +		}
> +		DW_TAG_enumerator {
> +		    {DW_AT_name THREE}
> +		    {DW_AT_const_value 3 DW_FORM_sdata}
> +		}
> +	    }
> +
> +	    subrange_label: DW_TAG_subrange_type {
> +		{lower_bound 1 DW_FORM_sdata}
> +		{upper_bound 2 DW_FORM_sdata}
> +		{type :$enum_label}
> +	    }
> +
> +	    DW_TAG_variable {
> +		{name rangeval}
> +		{type :$subrange_label}
> +		{const_value 2 DW_FORM_udata}
> +	    }
> +	}
> +    }
> +}
> +
> +if { [prepare_for_testing "failed to prepare" ${testfile} \
> +	  [list $srcfile $asm_file] {nodebug}] } {
> +    return -1
> +}
> +
> +gdb_test "print rangeval" " = TWO"
> diff --git a/gdb/valprint.c b/gdb/valprint.c
> index d6ec64845f4..c2ffe6224bf 100644
> --- a/gdb/valprint.c
> +++ b/gdb/valprint.c
> @@ -888,6 +888,14 @@ generic_value_print (struct value *val, struct ui_file *stream, int recurse,
>    if (is_fixed_point_type (type))
>      type = type->fixed_point_type_base_type ();
>  
> +  /* Widen a subrange to its target type, then use that type's
> +     printer.  */
> +  while (type->code () == TYPE_CODE_RANGE)
> +    {
> +      type = check_typedef (TYPE_TARGET_TYPE (type));
> +      val = value_cast (type, val);
> +    }
> +
>    switch (type->code ())
>      {
>      case TYPE_CODE_ARRAY:
> @@ -936,7 +944,6 @@ generic_value_print (struct value *val, struct ui_file *stream, int recurse,
>        generic_value_print_bool (val, stream, options, decorations);
>        break;
>  
> -    case TYPE_CODE_RANGE:
>      case TYPE_CODE_INT:
>        generic_value_print_int (val, stream, options);
>        break;
> -- 
> 2.34.1
> 

-- 
Joel