Re: [PATCH] Do not record a rejected target description

[Andrew Burgess <aburgess@redhat.com>]

Tom Tromey via Gdb-patches <gdb-patches@sourceware.org> writes:

> When connecting to a certain target, gdb issues a warning about the
> target description:
>
>     (gdb) target remote localhost:7947
>     Remote debugging using localhost:7947
>     warning: Architecture rejected target-supplied description
>
> If you then kill the inferior and change the exec-file, this will
> happen:
>
>     (gdb) file bar
>     Architecture of file not recognized.
>
> After this, debugging doesn't work very well.
>
> What happens here is that, despite the warning,
> target_find_description records the downloaded description in the
> target_desc_info.  Then the "file" command ends up calling
> set_gdbarch_from_file, which uses that description.
>
> It seems to me that, because the architecture rejected the
> description, it should not be used.  That is what this patch
> implements.
> ---
>  gdb/target-descriptions.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/gdb/target-descriptions.c b/gdb/target-descriptions.c
> index 1a451c79b82..38d0b3f8c7d 100644
> --- a/gdb/target-descriptions.c
> +++ b/gdb/target-descriptions.c
> @@ -565,7 +565,10 @@ target_find_description (void)
>  
>        info.target_desc = tdesc_info->tdesc;
>        if (!gdbarch_update_p (info))
> -	warning (_("Architecture rejected target-supplied description"));
> +	{
> +	  warning (_("Architecture rejected target-supplied description"));
> +	  tdesc_info->tdesc = nullptr;
> +	}

This seems fine, but it is possible that an exception could take us out
of this function too, for example, a misbehaving remote target can cause
target_read_description_xml to throw an exception.  I guess that any of
the issues you were originally seeing would also trigger if we throw an
exception.

I wonder if a better solution would be to use a RAII object to ensure
that tdesc_info->tdesc is always reset to nullptr on scope exit, then at
the end of target_find_description, after this line:

  tdesc_info->fetched = true;

we would call a method on the RAII object to indicate that it should NOT
clear the tdesc field.

Thanks,
Andrew