Re: [PATCH v2] Enable gdb.cp/ambiguous.exp with GCC and clang

[Pedro Alves <pedro@palves.net>]

On 8/27/20 11:39 AM, Gary Benson wrote:
> Luis Machado wrote:
>> On 8/25/20 11:21 AM, Gary Benson via Gdb-patches wrote:
>>> Pedro Alves wrote:
>>>> On 8/17/20 2:24 PM, Gary Benson wrote:
>>>>> Pedro Alves wrote:
>>>>>> On 7/27/20 2:09 PM, Gary Benson via Gdb-patches wrote:
>>>>>>> +    unsupported "compiler does not support -Wno-inaccessible-base"
>>>>>>
>>>>>> How about instead of bailing out, use "-Wno-inaccessible-base"
>>>>>> with GCC >= 10, and use "-w" with older GCCs?
>>>>>
>>>>> Sure.  How about this?
>>>>
>>>> OK.
>>>
>>> Thanks, I pushed it.
>>
>> I get the following, under Ubuntu 18.04 (GCC 7.x) with this commit...
>>
>> FAIL: gdb.cp/ambiguous.exp: print x.x
>> FAIL: gdb.cp/ambiguous.exp: print n.x
>> FAIL: gdb.cp/ambiguous.exp: print j.x
>> FAIL: gdb.cp/ambiguous.exp: print jva1.x
>> FAIL: gdb.cp/ambiguous.exp: print jva2.x
>> FAIL: gdb.cp/ambiguous.exp: print (A1)j
>> FAIL: gdb.cp/ambiguous.exp: print (A1)jva1
>>
>> Is the test really supposed to run with older GCC's?
> 
> Maybe not.  Though, I don't know what version of GCC it ought to start
> working on, so it's hard to know what to do.  I could leave the "-w"
> in for GCC < 10, and add an extra check to make it bail out for GCC
> <= your version, Luis?  With a suitable comment to mention that that's
> not set in stone?


I'm seeing it fail with GCC 9 and clang 10 as well.

Actually, the testcase can't be working _anywhere_.  It's
testing a feature that is gone from GDB. 

The testcase come in with the HP merge:

 +Sun Jan 10 23:44:11 1999  David Taylor  <taylor@texas.cygnus.com>
 +
 +
 +       The following files are part of the HP merge; some had longer
 +       names at HP, but have been renamed to be no more than 14
 +       characters in length.

Looking at the tree back then, we had:

 /* Helper function used by value_struct_elt to recurse through baseclasses.
    Look for a field NAME in ARG1. Adjust the address of ARG1 by OFFSET bytes,
    and search in it assuming it has (class) type TYPE.
    If found, return value, else return NULL.
 
    If LOOKING_FOR_BASECLASS, then instead of looking for struct fields,
    look for a baseclass named NAME.  */
 
 static value_ptr
 search_struct_field (name, arg1, offset, type, looking_for_baseclass)
      char *name;
      register value_ptr arg1;
      int offset;
      register struct type *type;
      int looking_for_baseclass;
 {
   int found = 0;
   char found_class[1024];
   value_ptr v;
   struct type *vbase = NULL;
 
   found_class[0] = '\000';
  
   v = search_struct_field_aux (name, arg1, offset, type, looking_for_baseclass, &found, found_class, &vbase);
   if (found > 1)
     warning ("%s ambiguous; using %s::%s. Use a cast to disambiguate.",
              name, found_class, name);
 
   return v;
 }

But search_struct_field does not handle the ambiguous field
case nowadays.  Somehow it got lost over the years.
That seems like a regression.  I wrote up a patch that adds
it back (though different), but it exposed other latent
bugs...  Sigh.  I'll post it soon.

Thanks,
Pedro Alves