[RFC][debug] Add -greadable-dwarf

[Tom de Vries]

On 08/20/2018 02:59 PM, Richard Biener wrote:
> On Wed, 15 Aug 2018, Tom de Vries wrote:
> 
>> Hi,
>>
>> This patch adds option -greadable-dwarf.  In absence of an DW_AT_comment
>> attribute,
> 
> What's a DW_AT_comment attribute?  I don't see this mentioned in the
> patch.
> 

It's a hypothetical DWARF attribute, that I would have preferred to use
instead of DW_AT_name.

>> it sets the DW_AT_name attribute of dies that otherwise do not get
>> that attribute, to make it easier to figure out what the die is describing.
>>
>> The option exports the names of artificial variables:
>> ...
>>  DIE    0: DW_TAG_variable (0x7fa934dd54b0)
>> +  DW_AT_name: "D.1922"
>>    DW_AT_type: die -> 0 (0x7fa934dd0d70)
>>    DW_AT_artificial: 1
>>
>> ...
>> which can be traced back to gimple dumps:
>> ...
>>   char a[0:D.1922] [value-expr: *a.0];
>> ...
>>
>> Furthermore, it adds names to external references:
>> ...
>>  DIE    0: DW_TAG_subprogram (0x7fa88b9650f0)
>> +DW_AT_name: "main"
>>  DW_AT_abstract_origin: die -> label: vla_1.c.6719312a + 29 (0x7fa88b965140)
>> ...
>>
>> This is an undocumented developer-only option, because using this option may
>> change behaviour of dwarf consumers, f.i., gdb shows the artificial variables:
>> ...
>> (gdb) info locals
>> a = 0x7fffffffda90 "\005"
>> D.4278 = <optimized out>
>> ...
>>
>> Any comments?
> 
> The idea is OK I guess but I'd call it -gforce-named-dies instead
> of -greadable-dwarf.

Done.

>  It also goes only half-way since it doesn't
> add names to DECL_NAMELESS vars.

I've tried to add that.

> There doesn't seem to be a convenient place to 
> 

?

>> Thanks,
>> - Tom
>>
>> [debug] Add -greadable-dwarf
>>
>> 2018-08-15  Tom de Vries  <tdevries@suse.de>
>>
>> 	* common.opt (greadable-dwarf): Add option.
>> 	* dwarf2out.c (add_name_and_src_coords_attributes): Add param. Add name
>> 	for artifical decls.
>> 	(add_decl_name): New function.
>> 	(dwarf2out_register_external_die): Add name to external reference die.
>>
>> ---
>>  gcc/common.opt  |  5 +++++
>>  gcc/dwarf2out.c | 24 +++++++++++++++++++++---
>>  2 files changed, 26 insertions(+), 3 deletions(-)
>>
>> diff --git a/gcc/common.opt b/gcc/common.opt
>> index b2f2215ecc6..6e5e0558e49 100644
>> --- a/gcc/common.opt
>> +++ b/gcc/common.opt
>> @@ -2972,6 +2972,11 @@ gstrict-dwarf
>>  Common Driver Report Var(dwarf_strict) Init(0)
>>  Don't emit DWARF additions beyond selected version.
>>  
>> +greadable-dwarf
>> +Common Driver Undocumented Report Var(flag_readable_dwarf) Init(0)
>> +Make generated dwarf more readable, at the cost of space and exposing compiler
>> +internals.
>> +
>>  gtoggle
>>  Common Driver Report Var(flag_gtoggle)
>>  Toggle debug information generation.
>> diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
>> index 4b63cbd8a1e..8c6b4372874 100644
>> --- a/gcc/dwarf2out.c
>> +++ b/gcc/dwarf2out.c
>> @@ -3824,7 +3824,9 @@ static void add_prototyped_attribute (dw_die_ref, tree);
>>  static dw_die_ref add_abstract_origin_attribute (dw_die_ref, tree);
>>  static void add_pure_or_virtual_attribute (dw_die_ref, tree);
>>  static void add_src_coords_attributes (dw_die_ref, tree);
>> -static void add_name_and_src_coords_attributes (dw_die_ref, tree, bool = false);
>> +static void add_name_and_src_coords_attributes (dw_die_ref, tree, bool = false,
>> +						bool = false);
>> +static void add_decl_name (dw_die_ref, tree);
>>  static void add_discr_value (dw_die_ref, dw_discr_value *);
>>  static void add_discr_list (dw_die_ref, dw_discr_list_ref);
>>  static inline dw_discr_list_ref AT_discr_list (dw_attr_node *);
>> @@ -6022,6 +6024,8 @@ dwarf2out_register_external_die (tree decl, const char *sym,
>>    else
>>      equate_decl_number_to_die (decl, die);
>>  
>> +  if (flag_readable_dwarf)
>> +    add_decl_name (die, decl);
> 
> Please use add_name_and_src_coords_attributes directly.
> 

Done.

>>    /* Add a reference to the DIE providing early debug at $sym + off.  */
>>    add_AT_external_die_ref (die, DW_AT_abstract_origin, sym, off);
>>  }
>> @@ -21269,7 +21273,8 @@ add_linkage_name (dw_die_ref die, tree decl)
>>  
>>  static void
>>  add_name_and_src_coords_attributes (dw_die_ref die, tree decl,
>> -				    bool no_linkage_name)
>> +				    bool no_linkage_name,
>> +				    bool no_src_coords_attributes)
>>  {
>>    tree decl_name;
>>  
>> @@ -21279,12 +21284,19 @@ add_name_and_src_coords_attributes (dw_die_ref die, tree decl,
>>        const char *name = dwarf2_name (decl, 0);
>>        if (name)
>>  	add_name_attribute (die, name);
>> -      if (! DECL_ARTIFICIAL (decl))
>> +      if (!no_src_coords_attributes && ! DECL_ARTIFICIAL (decl))
> 
> inconsistent spacing after !
> 

Done.

>>  	add_src_coords_attributes (die, decl);
>>  
>>        if (!no_linkage_name)
>>  	add_linkage_name (die, decl);
>>      }
>> +  else if (flag_readable_dwarf && decl_name == NULL)
>> +    {
>> +      char *buf = XNEWVEC (char, 32);
>> +      char decl_letter = TREE_CODE (decl) == CONST_DECL ? 'C' : 'D';
>> +      sprintf (buf, "%c.%u", decl_letter, DECL_UID (decl));
>> +      add_name_attribute (die, buf);
> 
> I think you leak 'buf'.
> 

Oops, fixed.

>> +    }
>>  
>>  #ifdef VMS_DEBUGGING_INFO
> 
> how does it interact with this VMS_DEBUGGING_INFO path?
> 

Um, AFAICT, not in any particular way,.

>>    /* Get the function's name, as described by its RTL.  This may be different
>> @@ -21298,6 +21310,12 @@ add_name_and_src_coords_attributes (dw_die_ref die, tree decl,
>>  #endif /* VMS_DEBUGGING_INFO */
>>  }
>>  
>> +static void
>> +add_decl_name (dw_die_ref die, tree decl)
>> +{
>> +  add_name_and_src_coords_attributes (die, decl, true, true);
>> +}
>> +
>>  /* Add VALUE as a DW_AT_discr_value attribute to DIE.  */
>>  
>>  static void
>>
>>
> 

Currently doing a bootstrap and reg-test on x86_64 of attached patch
with -gforce-named-dies enabled by default.

Thanks,
- Tom

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