Re: [patchv3] Fix crash on optimized-out entry data values

[Pedro Alves <palves@redhat.com>]

On 07/11/2014 04:37 PM, Jan Kratochvil wrote:
> On Wed, 09 Jul 2014 17:31:21 +0200, Jan Kratochvil wrote:
>> On Wed, 09 Jul 2014 13:52:00 +0200, Pedro Alves wrote:
>>> On 07/09/2014 11:33 AM, Jan Kratochvil wrote:
>>>> --- a/gdb/value.c
>>>> +++ b/gdb/value.c
>>>> @@ -198,12 +198,13 @@ struct value
>>>>    unsigned int lazy : 1;
>>>>  
>>>>    /* If nonzero, this is the value of a variable that does not
>>>> -     actually exist in the program.  If nonzero, and LVAL is
>>>> +     actually fully exist in the program.  If nonzero, and LVAL is
>>>>       lval_register, this is a register ($pc, $sp, etc., never a
>>>>       program variable) that has not been saved in the frame.  All
>>>>       optimized-out values are treated pretty much the same, except
>>>>       registers have a different string representation and related
>>>> -     error strings.  */
>>>> +     error strings.  It is true also for only partially optimized
>>>> +     out variables - see the 'unavailable' field below.  */
>>>>    unsigned int optimized_out : 1;
>>>>  
>>>>    /* If value is a variable, is it initialized or not.  */
>>>> @@ -334,7 +335,10 @@ struct value
>>>>       valid if lazy is nonzero.  */
>>>>    gdb_byte *contents;
>>>>  
>>>> -  /* Unavailable ranges in CONTENTS.  We mark unavailable ranges,
>>>> +  /* If OPTIMIZED_OUT is false then UNAVAILABLE must be VEC_empty
>>>> +     (not necessarily NULL).  
>>>
>>> Hmm, why?  We can collect only part of a non-optimized out value.
>>> What am I missing?
>>
>> I miss some documentation how these availability fields interact together.
> 
> From a comment in mail
> 	Message-Id: <201102071427.55970.pedro@codesourcery.com>
> 	We give preference to printing <optimized out> rather
> 	than <unavailable>, since if a value had been optimized out
> 	at compile time, it can never be collected at run-time.
> 
> it seems it is just reversed, that 'unavailable' can exist only for
> !optimized_out and it cannot exist for for optimized_out values.

Not really true either.  A value can be partially optimized out.
And then when e.g., inspecting a traceframe or a partial core dump,
the bits that are not optimized out may well not have been
collected, so those will be unavailable.  I'm sending you a different
patch in a bit.

-- 
Pedro Alves