RE: [PATCH 06/10] vla: update type from newly created value

["Agovic, Sanimir" <sanimir dot agovic at intel dot com>]

> -----Original Message-----
> From: Pedro Alves [mailto:palves@redhat.com]
> Sent: Wednesday, November 20, 2013 11:30 AM
> To: Agovic, Sanimir
> Cc: gdb-patches@sourceware.org
> Subject: Re: [PATCH 06/10] vla: update type from newly created value
> 
> On 10/21/2013 03:40 PM, Sanimir Agovic wrote:
> > Constructing a value based on a type and address might change the type
> > of the newly constructed value.
> 
> OOC (and for the archives), why's that?  Where does that occur?
> 
Since dwarf3 certain attributes e.g upper/lower bound may be computed
dynamically. To support such attributes with the current gdb type-system
we require such types to be "normalized". This means types with dynamic
properties are converted to types with static properties.
To successful convert a type with dynamic properties into one with static
properties access to inferior memory is needed. Therefore we hooked into
the following value constructors
value_at/value_at_lazy/value_from_contents_and_address
as they require an inferior address in addition to a type to instantiate
a value. IIF the passed type has dynamic properties we resolve the bounds
and thus change the type.

Given the following statement:

  struct value *val = value_at (my_vla_type, at_address);

Before this was always true:
  TYPE_LENGTH (value_type (val)) == TYPE_LENGTH (my_vla_type)

This is not the case after applying this (vla-c00) patch series. Type 
normalization is done in the mentioned value constructors and might 
change the value type, therefore we need to re-fetch the type from
the constructed value.

I hope this makes sense.

> > Thus re-fetch type via value_type to ensure
> > we have the correct type at hand.
> 
> --
> Pedro Alves

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