Re: Thoughts about GC root sets

[Paolo Bonzini <paolo dot bonzini at lu dot unisi dot ch>]

> Some of the GCC roots live on the heap memory, e.g. ident_table. These
> are not found by Boehm's GC by default. I've started fixing such
> places by registering these additional roots. But it got me thinking:
> how do the old GCC garbage collectors know about those roots? I do not
> see any root registration calls, but maybe I do not know where to
> look. They cannot handle such roots automatically because they don't
> intercept ordinary malloc calls and do not track information about
> such regions. So that's puzzling me. Any hints would be appreciated.

Labas Laurynas,

If you look closer at stringpool.c, you can see this:

  /* Mark the trees hanging off the identifier node for GGC.  These are
     handled specially (not using gengtype) because of the special
     treatment for strings.  */

  void
  ggc_mark_stringpool (void)
  {
    ht_forall (ident_hash, mark_ident, NULL);
  }

  /* Mark an identifier for GC.  */

  static int
  mark_ident (struct cpp_reader *pfile ATTRIBUTE_UNUSED, hashnode h,
              const void *v ATTRIBUTE_UNUSED)
  {
    gt_ggc_m_9tree_node (HT_IDENT_TO_GCC_IDENT (h));
    return 1;
  }

You can grep for ggc_mark_stringpool now, and you'll get to where other 
roots are taken from the tables that gengtype produces.  I'm not very 
familiar with the gengtype code and I haven't seen yours, so I can't 
tell you offhand how you can handle other GTY(()) variables.  This one 
*is* special though.

Paolo