Re: Dwarf2-related Internal error

Michal Ludvig
2003-08-14T14:56:01Z

Michal Ludvig told me that:
> Elena Zannoni told me that:
>
>> I don't have much time to devote to this, but usually that kind of
>> error is generated by some infinite loop that gdb got itself into.
>
>
> Unlikely. The immediate problem is that the size of function's parameter
> 'xx' is too big:
>
> (top-gdb) f
> #0 read_var_value (var=0x8b35c0, frame=0x85ad98)
> at ../../gdb-head/gdb/findvar.c:397
> 397 struct type *type = SYMBOL_TYPE (var);
> (top-gdb) p *var->type
> $2 = {pointer_type = 0x0, reference_type = 0x0, chain = 0x89fc00,
> instance_flags = 0, length = 4294967292, main_type = 0x89fc28}
> (top-gdb) p (int)4294967292
> $3 = -4
> (top-gdb)
>
> Very likely it was ment to be -4 because something somewhere in the
> debug info was wrongly interpreted.

OK, I have found the problem. The type of the parameter 'xx' is an array
with unspecified size. Lower bound is set to '1' for Fortran and since
there is no upper bound specified, it's set to '-1' by default.

3097 else if (attr->form == DW_FORM_block1)
3098 {
3099 /* GCC encodes arrays with unspecified or dynamic length
3100 with a DW_FORM_block1 attribute.
3101 FIXME: GDB does not yet know how to handle dynamic
3102 arrays properly, treat them as arrays with unspecified
3103 length for now. */
3104 high = -1;
3105 }

Later, when the actual size of the array type is computed, it takes the
size of the main type (real, size=4) and multiplies it by
(high-low+1=-1) leading to -4 which is quite a big number when converted
to unsigned.

Now how to solve it. For now I did

length for now. */
high = -1;
+ if (cu_language == language_fortran)
+ high = 0;
}

which at least prevents GDB from crashing. IMHO it achieves the same
behaviour as for other languages, where low=0, high=-1 and so the size
of the array results to 0. In fortran low=1, so with high=0 the size
will become 0 as well.

Would this be an acceptable solution? Any comments?