Re: [PATCH][gdb/testsuite] Don't use default form in Dwarf::_guess_form

[Simon Marchi <simark@simark.ca>]

On 2020-10-23 7:46 a.m., Tom de Vries wrote:
> Hi,
>
> The only possible form for a DW_AT_low_pc attribute is DW_FORM_addr.
>
> When specifying in dwarf assembly a low_pc attribute without explicit form:
> ...
>   {low_pc {main_label - 4}}
> ...
> the resulting attribute uses DW_FORM_string, which is misinterpreted by gdb
> when reading it as:
> ...
>         cu->base_address = attr->as_address ();
> ...
>
> Stop using DW_FORM_string as default form.  Instead, use a default form based
> on the attribute name, if possible and unambiguous.  Otherwise, error out.
>
> F.i.:
> - for DW_AT_low_pc we use DW_FORM_addr.
> - For DW_AT_high_pc, we don't specify a default form because it could be
>   either address or constant class.
> - For DW_AT_name, we use DW_FORM_string.  While we could encode with
>   DW_FORM_strp instead, DW_FORM_string is always ok.
>
> Tested on x86_64-linux.
>
> Any comments?
>
> Thanks,
> - Tom

I like it, I like specifying explicit forms in any case.

I think it makes the "If the value looks like an integer, a form is
required." redundant though.  You could remove it, in which case
specifying an integer attribute without a form would fall in the "No
form for..." error branch.

Simon