Re: [PATCH 2/3] gdb: break up core_target initialization

[John Baldwin <jhb@FreeBSD.org>]

On 11/28/22 6:50 PM, Simon Marchi via Gdb-patches wrote:
> In the core target constructor, we currently have to jump through some
> hoops to read the auxv data from the core, in order to choose an
> appropriate gdbarch for the inferior.  The core BFD gives us a gdbarch,
> but it might not tell the whole story.  By reading some auxv fields,
> some architectures are able to choose a more specific gdbarch.  The
> problem is that to read auxv from the core using the inferior's target
> stack, the core target needs to be pushed on the inferior's target
> stack.  But this work is done in the core target constructor, so it
> can't be pushed at this point.  The current solution is to pass a
> pointer to the core target to gdbarch_core_read_description, in
> core_target::read_description.  That "hack" must then propagate to many
> functions involved in selecting the architecture and reading auxv.
> 
> With this patch, I propose to break things up to avoid the problem.  The
> core_target constructor will now do only trivial stuff that doesn't need
> to call things outside core_target.  Then, we'll push the core_target on
> the inferior's target stack.  And finally, complete the initialization
> that potentially requires doing target calls.  The target calls to read
> auxv at this point will just be regular target calls.

I think this is a nice solution to the problem.
  
> diff --git a/gdb/corelow.c b/gdb/corelow.c
> index 293bc8d4f593..c8cd5b7a2570 100644
> --- a/gdb/corelow.c
> +++ b/gdb/corelow.c
> @@ -72,6 +72,13 @@ class core_target final : public process_stratum_target
>   public:
>     core_target ();
>   
> +  /* Complete the initialization.
> +
> +     Called after construction, after pushing the target to the inferior's
> +     target stack, so that arches are can do target calls, for instance to read
> +     auxv.  */
> +  void initialize ();

s/arches are can/arches can/

> @@ -170,7 +177,11 @@ core_target::core_target ()
>     /* Find a first arch based on the BFD.  We need the initial gdbarch so
>        we can setup the hooks to find a target description.  */
>     m_core_gdbarch = gdbarch_from_bfd (core_bfd);
> +}
>   
> +void
> +core_target::initialize ()
> +{
>     /* If the arch is able to read a target description from the core, it
>        could yield a more specific gdbarch.  */
>     const struct target_desc *tdesc = read_description ();

I do wonder if the comments above want expanding slightly as we are now in a
new function and over time it might move around in the file so that these
two comments aren't right next to each other?  Maybe something like like:

     /* Find a first arch based on the BFD.  We need the initial gdbarch so
        we can provide a barebones target able to read information such as
        auxv data.  The final gdbarch will be set in initialize.  */
     m_core_gdbarch = gdbarch_from_bfd (core_bfd);
}

void
core_target::initialize ()
{
     /* If the initial arch from the BFD is able to read a target description
        from the core, it could yield a more specific gdbarch.  */


-- 
John Baldwin