RE: [PATCH v4 2/2] gdb, dwarf: create symbols for template tags without names

["Kempke, Nils-Christian via Gdb-patches" <gdb-patches@sourceware.org>]

> -----Original Message-----
> From: Bruno Larsen <blarsen@redhat.com>
> Sent: Thursday, August 25, 2022 4:05 PM
> To: Kempke, Nils-Christian <nils-christian.kempke@intel.com>; gdb-
> patches@sourceware.org
> Cc: tom@tromey.com
> Subject: Re: [PATCH v4 2/2] gdb, dwarf: create symbols for template tags
> without names
> 
> 
> On 24/08/2022 11:18, Nils-Christian Kempke wrote:
> > The following GDB behavior was also reported as a GDB bug in
> >
> >    https://sourceware.org/bugzilla/show_bug.cgi?id=28396
> >
> > I will reiterate the problem a bit and give some more information here.
> > This patch closes the above mentioned bug.
> >
> > The DWARF 5 standard 2.23 'Template Parameters' reads:
> >
> >     A template type parameter is represented by a debugging information
> >     entry with the tag DW_TAG_template_type_parameter.  A template
> value
> >     parameter is represented by a debugging information entry with the tag
> >     DW_TAG_template_value_parameter.  The actual template parameter
> entries
> >     appear in the same order as the corresponding template formal
> >     parameter declarations in the source progam.
> >
> >     A type or value parameter entry may have a DW_AT_name attribute,
> whose
> >     value is a null-terminated string containing the name of the
> >     corresponding formal parameter.
> >
> > So the DW_AT_name attribute for DW_TAG_template_type_parameter
> and
> > DW_TAG_template_value_parameter is optional.
> >
> > Within GDB, creating a new symbol from some read DIE usually requires
> the
> > presence of a DW_AT_name for the DIE (an exception here is the case of
> > unnamed namespaces or the existence of a linkage name).
> >
> > This patch makes the presence of the DW_AT_name for template
> value/type
> > tags optional, similar to the unnamed namespaces.
> >
> > For unnamed namespaces dwarf2_name simply returns the constant string
> > CP_ANONYMOUS_NAMESPACE_STR '(anonymous namespace)'.  For
> template tags a
> > case was added to the switch statement calling the
> > unnamed_template_tag_name helper.  Within the scope of parent which
> > the template parameter is a child of, the helper counts the position
> > of the template tag within the unnamed template tags and returns
> > '<unnamedNUMBER>' where NUMBER is its position.  This way we end up
> with
> > unique names within the respective scope of the function/class/struct
> > (these are the only currenltly supported template kinds within GDB and
> > usually the compilers) where we discovered the template tags in.
> >
> > While I do not know of a way to bring GCC to emit template tags without
> > names there is one for clang/icpx.  Consider the following example
> >
> >    template<typename A, typename B, typename C>
> >    class Foo {};
> >
> >    template<typename, typename B, typename>
> >    class Foo;
> >
> >    int main () {
> >      Foo<double, int, float> f;
> >      return 0;
> >    }
> >
> > The forward declaration for 'Foo' with the missing template type names
> > 'A' and 'C' makes clang emit a bunch of template tags without names:
> >
> >   ...
> >    <2><43>: Abbrev Number: 3 (DW_TAG_variable)
> >      <44>   DW_AT_location    : 2 byte block: 91 78      (DW_OP_fbreg: -8)
> >      <47>   DW_AT_name        : (indirect string, offset: 0x63): f
> >      <4b>   DW_AT_decl_file   : 1
> >      <4c>   DW_AT_decl_line   : 8
> >      <4d>   DW_AT_type        : <0x59>
> >   ...
> >   <1><59>: Abbrev Number: 5 (DW_TAG_class_type)
> >      <5a>   DW_AT_calling_convention: 5  (pass by value)
> >      <5b>   DW_AT_name        : (indirect string, offset: 0x74): Foo<double, int,
> float>
> >      <5f>   DW_AT_byte_size   : 1
> >      <60>   DW_AT_decl_file   : 1
> >      <61>   DW_AT_decl_line   : 2
> >   <2><62>: Abbrev Number: 6 (DW_TAG_template_type_param)
> >      <63>   DW_AT_type        : <0x76>
> >   <2><67>: Abbrev Number: 7 (DW_TAG_template_type_param)
> >      <68>   DW_AT_type        : <0x52>
> >      <6c>   DW_AT_name        : (indirect string, offset: 0x6c): B
> >   <2><70>: Abbrev Number: 6 (DW_TAG_template_type_param)
> >      <71>   DW_AT_type        : <0x7d>
> >   ...
> >
> > Befor this patch, GDB would not create any symbols for the read template
> 
> Hi Nils,
> 
> Thanks for working on this. There is a small typo at the start of this
> sentence, but other than this, this patch, and the previous one, looks
> ready to go for me. Let's see if Tromey agrees and approves it.
> 
> --
> Cheers,
> Bruno

Hi Bruno,

Thanks, yes.. I fixed it locally now.

Cheers,
Nils
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