[1/2] gdb/testsuite: add test for negative subrange bounds with unsigned form

  I am looking at this code [1]:

  /* Normally, the DWARF producers are expected to use a signed
     constant form (Eg. DW_FORM_sdata) to express negative bounds.
     But this is unfortunately not always the case, as witnessed
     with GCC, for instance, where the ambiguous DW_FORM_dataN form
     is used instead.  To work around that ambiguity, we treat
     the bounds as signed, and thus sign-extend their values, when
     the base type is signed.  */
  negative_mask =
    -((ULONGEST) 1 << (base_type->length () * TARGET_CHAR_BIT - 1));
  if (low.kind () == PROP_CONST
      && !base_type->is_unsigned () && (low.const_val () & negative_mask))
    low.set_const_val (low.const_val () | negative_mask);
  if (high.kind () == PROP_CONST
      && !base_type->is_unsigned () && (high.const_val () & negative_mask))
    high.set_const_val (high.const_val () | negative_mask);

Nothing in the testsuite seems to exercise it, as when I remove it, all
of gdb.dwarf2 still passes.  And tests in other directories would be
compiler-dependent, so would rely on having a buggy compiler.

Update gdb.dwarf2/subrange.exp to have a test for it.  When removing the
code above, the new test fails with:

  ptype array_with_buggy_negative_bounds_type^M
  type = array [240..244] of signed_byte^M
  (gdb) FAIL: gdb.dwarf2/subrange.exp: ptype array_with_buggy_negative_bounds_type

instead of the expected:

  ptype array_with_buggy_negative_bounds_type^M
  type = array [-16..-12] of signed_byte^M
  (gdb) PASS: gdb.dwarf2/subrange.exp: ptype array_with_buggy_negative_bounds_type

[1] https://gitlab.com/gnutools/binutils-gdb/-/blob/5ea14aa4e53fa37f4ba4517497ed2c1e4c60dee2/gdb/dwarf2/read.c#L17681-17695

Change-Id: I1992a3ff0cb1e90fa8a9114dae6c591792f059c2
---
 gdb/testsuite/gdb.dwarf2/subrange.exp | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)
  

Simon Marchi via Gdb-patches <gdb-patches@sourceware.org> writes:

> I am looking at this code [1]:
>
>   /* Normally, the DWARF producers are expected to use a signed
>      constant form (Eg. DW_FORM_sdata) to express negative bounds.
>      But this is unfortunately not always the case, as witnessed
>      with GCC, for instance, where the ambiguous DW_FORM_dataN form
>      is used instead.  To work around that ambiguity, we treat
>      the bounds as signed, and thus sign-extend their values, when
>      the base type is signed.  */
>   negative_mask =
>     -((ULONGEST) 1 << (base_type->length () * TARGET_CHAR_BIT - 1));
>   if (low.kind () == PROP_CONST
>       && !base_type->is_unsigned () && (low.const_val () & negative_mask))
>     low.set_const_val (low.const_val () | negative_mask);
>   if (high.kind () == PROP_CONST
>       && !base_type->is_unsigned () && (high.const_val () & negative_mask))
>     high.set_const_val (high.const_val () | negative_mask);
>
> Nothing in the testsuite seems to exercise it, as when I remove it, all
> of gdb.dwarf2 still passes.  And tests in other directories would be
> compiler-dependent, so would rely on having a buggy compiler.
>
> Update gdb.dwarf2/subrange.exp to have a test for it.  When removing the
> code above, the new test fails with:
>
>   ptype array_with_buggy_negative_bounds_type^M
>   type = array [240..244] of signed_byte^M
>   (gdb) FAIL: gdb.dwarf2/subrange.exp: ptype array_with_buggy_negative_bounds_type
>
> instead of the expected:
>
>   ptype array_with_buggy_negative_bounds_type^M
>   type = array [-16..-12] of signed_byte^M
>   (gdb) PASS: gdb.dwarf2/subrange.exp: ptype array_with_buggy_negative_bounds_type
>
> [1] https://gitlab.com/gnutools/binutils-gdb/-/blob/5ea14aa4e53fa37f4ba4517497ed2c1e4c60dee2/gdb/dwarf2/read.c#L17681-17695
>
> Change-Id: I1992a3ff0cb1e90fa8a9114dae6c591792f059c2
> ---
>  gdb/testsuite/gdb.dwarf2/subrange.exp | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
>
> diff --git a/gdb/testsuite/gdb.dwarf2/subrange.exp b/gdb/testsuite/gdb.dwarf2/subrange.exp
> index 72d7babc88e..8a8443f31a8 100644
> --- a/gdb/testsuite/gdb.dwarf2/subrange.exp
> +++ b/gdb/testsuite/gdb.dwarf2/subrange.exp
> @@ -28,6 +28,7 @@ Dwarf::assemble $asm_file {
>   	compile_unit {{language @DW_LANG_Pascal83}} {
>  	    declare_labels byte_label typedef_label array_label
>  
> +	    # A subrange's underlying type that is a typedef.
>  	    byte_label: base_type {
>  		{name byte}
>  		{encoding @DW_ATE_unsigned}
> @@ -54,6 +55,28 @@ Dwarf::assemble $asm_file {
>  		{name TByteArray}
>  		{type :$array_label}
>  	    }
> +
> +	    # This subrange's underlying type is signed, but the bounds are
> +	    # specified using a non-signed form.
> +	    declare_labels signed_byte_label subrange_with_buggy_negative_bounds_label
> +
> +	    signed_byte_label: base_type {
> +		{name signed_byte}
> +		{encoding @DW_ATE_signed}
> +		{byte_size 1 DW_FORM_sdata}
> +	    }
> +
> +	    # The bounds mean -16 to -12.
> +	    subrange_with_buggy_negative_bounds_label: subrange_type {
> +		{lower_bound 0xf0 DW_FORM_udata}
> +		{upper_bound 0xf4 DW_FORM_udata}
> +		{type :$signed_byte_label}
> +	    }
> +
> +	    DW_TAG_variable {
> +		{name subrange_with_buggy_negative_bounds_variable}
> +		{type :$subrange_with_buggy_negative_bounds_label}
> +	    }
>  	}
>      }
>  }
> @@ -67,3 +90,5 @@ gdb_test_no_output "set language pascal"
>  
>  gdb_test "ptype TByteArray" \
>      "type = array \\\[0\\.\\.191\\\] of byte"
> +gdb_test "ptype subrange_with_buggy_negative_bounds_variable" \
> +    "type = -16..-12"

Should be "type = -16\\.\\.-12"

Otherwise, looks good.

Thanks,
Andrew

> -- 
> 2.39.1
  

>> @@ -67,3 +90,5 @@ gdb_test_no_output "set language pascal"
>>  
>>  gdb_test "ptype TByteArray" \
>>      "type = array \\\[0\\.\\.191\\\] of byte"
>> +gdb_test "ptype subrange_with_buggy_negative_bounds_variable" \
>> +    "type = -16..-12"
> 
> Should be "type = -16\\.\\.-12"

Indeed, fixed.

> Otherwise, looks good.

Thanks, will push.

Simon