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Re: Trivial fix in value_sub
- From: Michael Snyder <msnyder at redhat dot com>
- To: Jim Blandy <jimb at redhat dot com>
- Cc: Jim Ingham <jingham at apple dot com>, gdb-patches at sources dot redhat dot com
- Date: Wed, 03 Apr 2002 15:44:26 -0800
- Subject: Re: Trivial fix in value_sub
- Organization: Red Hat, Inc.
- References: <76AD507E-436C-11D6-890B-000393540DDC@apple.com> <np3cyce6o4.fsf@zwingli.cygnus.com>
Jim Blandy wrote:
>
> (Thanks for making value_add and value_sub consistent!)
>
> If I use an incomplete type in my program --- say, by making a
> definition like this:
>
> struct foo *x;
>
> where there is no definition for `struct foo' in scope --- does GDB
> set TYPE_LENGTH (TYPE_TARGET_TYPE (p)) to zero, where `p' is the type
> of x?
>
> See, that code in value_add (and now in value_sub) is supposed to
> handle void *; as an extension, GCC allows arithmetic on void *
> values, treating sizeof (void) as one. This makes sense for void *
> values, since they're often used as pointers to raw memory.
>
> However, for things like incomplete struct types, treating the size as
> one is completely bogus. That's surely not the behavior the user
> would expect; they may not even realize that the type is incomplete.
I agree -- I think taking the sizeof an incomplete type should
result in an error, just as it would in c/c++.
> If GDB really does set the length of an incomplete struct type to
> zero, then that code should really read something like:
>
> if (sz == 0 && TYPE_CODE (TYPE_TARGET_TYPE (type1)) == TYPE_CODE_VOID)
> sz = 1;
>
> Can you tell me more about the context in which you noticed this
> problem?
Heh -- I bet I know. ;-)