[PATCH] gdb: handle non-const property types in ada_modulus (PR ada/26318)

[Tom de Vries]

On 7/30/20 5:03 PM, Simon Marchi via Gdb-patches wrote:
> PR 26318 shows that running `maint print symbols` on an Ada binary,
> compiled with an Ada distribution that includes debug info for the
> standard library, triggers this assertion:
> 
>     /home/simark/src/binutils-gdb/gdb/gdbtypes.h:526: internal-error: LONGEST dynamic_prop::const_val() const: Assertion `m_kind == PROP_CONST' failed.
> 
> The problem is in particular when printing type
> `system__object_reader__decoded_ada_name__TTdecodedSP1___XDL_0`, which
> has a dynamic high bound (PROP_LOCLIST kind).  When printing a concrete
> value of this type, this type gets resolved to a type with a constant
> high bound, so ada_modulus can return this constant value.
> 
> However, when printing the dynamic range type on its own, such as with
> `maint print symbols`, the high bound is still of kind PROP_LOCLIST.
> When ada_modulus tries to access the property as a const value, the
> assert triggers.
> 
> There's no sensible numerical value to return in this case.  Ideally,
> ada_modulus would return something to the caller indicating that the
> value is dynamic and therefore can't be returned as an integer.  The
> callers would handle it, for example `maint print symbols` would say
> that the high bound of the type is dynamic.
> 
> However, this patch implements the simpler fix of returning 0 in that
> case.  It kind of restores the previous behavior of before we validated
> the dynamic property kind in the getters, where we would just return
> whatever random integer value was in `const_val`.  Except now it's
> consistently 0.
> 
> This is what we had before we added dynamic property getters:
> 
> $ ./gdb -q ~/foo -ex "maint expand-symtabs" -ex "maint print symbols" -batch | grep 'typedef <system__object_reader__decoded_ada_name__TTdecodedSP1'
>      typedef <system__object_reader__decoded_ada_name__TTdecodedSP1: mod 107820865988257;
> 
> and this is what we have now:
> 
> $ ./gdb -q ~/foo -ex "maint expand-symtabs" -ex "maint print symbols" -batch | grep 'typedef <system__object_reader__decoded_ada_name__TTdecodedSP1'
>      typedef <system__object_reader__decoded_ada_name__TTdecodedSP1: mod 0;
> 
> The value 107820865988257 is the `baton` field of the property's union
> interpreted as an integer, so a bogus value.
> 
> gdb/ChangeLog:
> 
> 	PR ada/26318
> 	* ada-lang.c (ada_modulus): Return 0 if property is not of const
> 	kind.
> 
> Change-Id: I3f6d343a9c3cd7cd62a4fc591943a43541223d50
> ---
>  gdb/ada-lang.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
> index 2be3fe45b35d..29951528e5e5 100644
> --- a/gdb/ada-lang.c
> +++ b/gdb/ada-lang.c
> @@ -11452,7 +11452,14 @@ ada_is_modular_type (struct type *type)
>  ULONGEST
>  ada_modulus (struct type *type)
>  {
> -  return (ULONGEST) type->bounds ()->high.const_val () + 1;
> +  const dynamic_prop &high = type->bounds ()->high;
> +
> +  if (high.kind () == PROP_CONST)
> +    return (ULONGEST) high.const_val () + 1;
> +
> +  /* If TYPE is unresolved, the high bound might be a location list.  Return
> +     0, for lack of a better value to return.  */
> +  return 0;
>  }
>  


Hi,

not an ada-maintainer, but LGTM.

Thanks,
- Tom