Re: MPS: assertion failed: header_type (h) != IGC_OBJ_FWD

[Pip Cet <pipcet@protonmail.com>]

On Tuesday, July 16th, 2024 at 14:48, Gerd Möllmann <gerd.moellmann@gmail.com> wrote:
> Helmut Eller eller.helmut@gmail.com writes:
> 
> > On Tue, Jul 16 2024, Gerd Möllmann wrote:
> > 
> > > That's probably a misunderstanding. I'm thinking about a block of memory
> > > containing references, and the alignment of these references, not the
> > > alignment of the block.
> > > 
> > > Example with sizeof(int) = 4, and sizeof(void *) = 8
> > > 
> > > struct x
> > > {
> > > int x;
> > > struct Lisp_Symbol *s;
> > > };
> > > 
> > > What about the offset of x::s?
> > 
> > That's not a problem because offsetof(struct x, s) = 8. There are 4
> > bytes padding after x. A problem could be if an unaligned void* is cast
> > to a struct Lisp_Symbol*; let's hope that nobody does that.
> 
> 
> If you're right, and the same holds for the control stack and anything
> else a malloc'd block can contain, then we're safe.

I'm pretty sure we are, though interior pointers might cause a problem.

Any leads on where the crash happens yet? I've found a breakpoint on wrong_type_argument helpful, since we usually hit that when memory moves and the old pointer doesn't point to an object of the right type.

By the way, I'm done with the code for making base == client pointers and giving (almost) every object a header. Since it's a major change and can't really be split that well, I'm not sure yet how to install it, though it needs to be cleaned up still in any case... But when I do install it, it will require rebuilding of all .eln files, or there will be weird segfaults. (I guess we could bump the ABI constant in the nativecomp code to avoid that).

Pip