[PING][PATCH][gdb/symtab] Handle DW_AT_decl_file with form DW_FORM_implicit_const

[Tom de Vries <tdevries@suse.de>]

On 2/5/21 1:28 PM, Tom de Vries wrote:
> Hi,
> 
> With test-case gdb.cp/temargs.exp on target board \
> unix/gdb:debug_flags=-gdwarf-5 I run into:
> ...
> (gdb) info addr I^M
> ERROR: GDB process no longer exists
> GDB process exited with wait status 32286 exp19 0 0 CHILDKILLED SIGABRT SIGABRT
> UNRESOLVED: gdb.cp/temargs.exp: test address of I in templ_m
> ...
> 
> This is a regression since commit 529908cbd0a "Remove DW_UNSND".
> 
> The problem is that this DW_AT_decl_file:
> ...
>  <1><221>: Abbrev Number: 4 (DW_TAG_structure_type)
>     <222>   DW_AT_name        : Base<double, 23, (& a_global), &S::f>
>     <226>   DW_AT_byte_size   : 1
>     <226>   DW_AT_decl_file   : 1
>     <226>   DW_AT_decl_line   : 30
>     <227>   DW_AT_sibling     : <0x299>
> ...
> is not read by this code in new_symbol:
> ....
>       attr = dwarf2_attr (die,
>                           inlined_func ? DW_AT_call_file : DW_AT_decl_file,
>                           cu);
>       if (attr != nullptr && attr->form_is_unsigned ())
> ...
> because DW_AT_decl_file has form DW_FORM_implicit_const:
> ...
>    4      DW_TAG_structure_type    [has children]
>     DW_AT_name         DW_FORM_strp
>     DW_AT_byte_size    DW_FORM_implicit_const: 1
>     DW_AT_decl_file    DW_FORM_implicit_const: 1
>     DW_AT_decl_line    DW_FORM_data1
>     DW_AT_sibling      DW_FORM_ref4
>     DW_AT value: 0     DW_FORM value: 0
> ...
> which is a signed LEB128, so attr->form_is_unsigned () returns false.
> 
> Fix this by introducing new functions is_nonnegative and as_nonnegative, and
> use these instead of form_is_unsigned and as_unsigned.
> 
> Tested on x86_64-linux.
> 
> Any comments?
> 

Ping.

Thanks,
- Tom

> [gdb/symtab] Handle DW_AT_decl_file with form DW_FORM_implicit_const
> 
> gdb/ChangeLog:
> 
> 2021-02-05  Tom de Vries  <tdevries@suse.de>
> 
> 	PR symtab/27336
> 	* dwarf2/attribute.c (attribute::form_is_signed): New function
> 	factored out of ...
> 	* dwarf2/attribute.h (attribute::as_signed): ... here.
> 	(attribute::is_nonnegative, attribute::as_nonnegative): New function.
> 	(attribute::form_is_signed): Declare.
> 	* dwarf2/read.c (new_symbol): Use is_nonnegative and as_nonnegative
> 	for DW_AT_decl_file.
> 
> ---
>  gdb/dwarf2/attribute.c |  8 ++++++++
>  gdb/dwarf2/attribute.h | 27 ++++++++++++++++++++++++++-
>  gdb/dwarf2/read.c      |  4 ++--
>  3 files changed, 36 insertions(+), 3 deletions(-)
> 
> diff --git a/gdb/dwarf2/attribute.c b/gdb/dwarf2/attribute.c
> index b4f188a096e..8c58f1bcd9f 100644
> --- a/gdb/dwarf2/attribute.c
> +++ b/gdb/dwarf2/attribute.c
> @@ -189,6 +189,14 @@ attribute::form_is_unsigned () const
>  
>  /* See attribute.h.  */
>  
> +bool
> +attribute::form_is_signed () const
> +{
> +  return form == DW_FORM_sdata || form == DW_FORM_implicit_const;
> +}
> +
> +/* See attribute.h.  */
> +
>  bool
>  attribute::form_requires_reprocessing () const
>  {
> diff --git a/gdb/dwarf2/attribute.h b/gdb/dwarf2/attribute.h
> index 56776d64ed3..b0b3e14cc68 100644
> --- a/gdb/dwarf2/attribute.h
> +++ b/gdb/dwarf2/attribute.h
> @@ -70,7 +70,7 @@ struct attribute
>       form.  */
>    LONGEST as_signed () const
>    {
> -    gdb_assert (form == DW_FORM_sdata || form == DW_FORM_implicit_const);
> +    gdb_assert (form_is_signed ());
>      return u.snd;
>    }
>  
> @@ -92,6 +92,28 @@ struct attribute
>      return u.unsnd;
>    }
>  
> +  /* Return true if the value is nonnegative.  Requires that that
> +     reprocessing not be needed.  */
> +  bool is_nonnegative () const
> +  {
> +    if (form_is_unsigned ())
> +      return true;
> +    if (form_is_signed ())
> +      return as_signed () >= (LONGEST)0;
> +    return false;
> +  }
> +
> +  /* Return the nonnegative value.  Requires that that reprocessing not be
> +     needed.  */
> +  ULONGEST as_nonnegative () const
> +  {
> +    if (form_is_unsigned ())
> +      return as_unsigned ();
> +    if (form_is_signed ())
> +      return (ULONGEST)as_signed ();
> +    gdb_assert (false);
> +  }
> +
>    /* Return non-zero if ATTR's value is a section offset --- classes
>       lineptr, loclistptr, macptr or rangelistptr --- or zero, otherwise.
>       You may use the as_unsigned method to retrieve such offsets.
> @@ -147,6 +169,9 @@ struct attribute
>    /* Check if the attribute's form is an unsigned integer form.  */
>    bool form_is_unsigned () const;
>  
> +  /* Check if the attribute's form is a signed integer form.  */
> +  bool form_is_signed () const;
> +
>    /* Check if the attribute's form is a form that requires
>       "reprocessing".  */
>    bool form_requires_reprocessing () const;
> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
> index 98189f7b566..424a0da3d6c 100644
> --- a/gdb/dwarf2/read.c
> +++ b/gdb/dwarf2/read.c
> @@ -22180,10 +22180,10 @@ new_symbol (struct die_info *die, struct type *type, struct dwarf2_cu *cu,
>        attr = dwarf2_attr (die,
>  			  inlined_func ? DW_AT_call_file : DW_AT_decl_file,
>  			  cu);
> -      if (attr != nullptr && attr->form_is_unsigned ())
> +      if (attr != nullptr && attr->is_nonnegative ())
>  	{
>  	  file_name_index file_index
> -	    = (file_name_index) attr->as_unsigned ();
> +	    = (file_name_index) attr->as_nonnegative ();
>  	  struct file_entry *fe;
>  
>  	  if (cu->line_header != NULL)
>