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NULLSTACK fixes for nonlocal exits in reentrant pre-wind handlers

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* libguile/vm-i-system.c (goto/cc): Add some asserts here.

* libguile/vm.c (capture_vm_cont): Add some asserts here too.
  (reinstate_vm_cont): Null the correct number of bytes. Add a FIXME.
  (vm_reset_stack): Make the code a bit clearer. Null the correct number
  of bytes.

* libguile/vm-engine.h (NULLSTACK_FOR_NONLOCAL_EXIT): New macro, handles
  a very tricky case that took me days to find! Amply commented. Expands
  to nothing in the normal case.

* libguile/vm-i-system.c (call, goto/args, mv-call): Call
  NULLSTACK_FOR_NONLOCAL_EXIT in the right places. Fixes
  continuations.test.
This commit is contained in:
Andy Wingo 2008-10-09 14:44:43 +02:00
parent 0570c3f197
commit 66db076ae1
3 changed files with 24 additions and 5 deletions
Download patch file Download diff file Expand all files Collapse all files

7
libguile/vm-engine.h
View file

@ -247,10 +247,17 @@
# define CHECK_STACK_LEAKN(_n) ASSERT (!sp[_n]);
# define CHECK_STACK_LEAK() CHECK_STACK_LEAKN(1)
# define NULLSTACK(_n) { int __x = _n; CHECK_STACK_LEAKN (_n+1); while (__x > 0) sp[__x--] = NULL; }
/* If you have a nonlocal exit in a pre-wind proc while invoking a continuation
inside a dynwind (phew!), the stack is fully rewound but vm_reset_stack for
that continuation doesn't have a chance to run. It's not important on a
semantic level, but it does mess up our stack nulling -- so this macro is to
fix that. */
# define NULLSTACK_FOR_NONLOCAL_EXIT() if (vp->sp > sp) NULLSTACK (vp->sp - sp);
#else
# define CHECK_STACK_LEAKN(_n)
# define CHECK_STACK_LEAK()
# define NULLSTACK(_n)
# define NULLSTACK_FOR_NONLOCAL_EXIT()
#endif
#define CHECK_OVERFLOW() \

6
libguile/vm-i-system.c
View file

@ -567,6 +567,7 @@ VM_DEFINE_INSTRUCTION (call, "call", 1, -1, 1)
SYNC_REGISTER ();
/* keep args on stack so they are marked */
sp[-1] = scm_apply (x, sp[0], SCM_EOL);
NULLSTACK_FOR_NONLOCAL_EXIT ();
/* FIXME what if SCM_VALUESP(*sp) */
DROP ();
NEXT;
@ -754,6 +755,7 @@ VM_DEFINE_INSTRUCTION (goto_args, "goto/args", 1, -1, 1)
POP_LIST (nargs);
SYNC_REGISTER ();
sp[-1] = scm_apply (x, sp[0], SCM_EOL);
NULLSTACK_FOR_NONLOCAL_EXIT ();
DROP ();
/* FIXME what if SCM_VALUESP(*sp) */
goto vm_return;
@ -822,6 +824,7 @@ VM_DEFINE_INSTRUCTION (mv_call, "mv-call", 3, -1, 1)
POP_LIST (nargs);
SYNC_REGISTER ();
sp[-1] = scm_apply (x, sp[0], SCM_EOL);
NULLSTACK_FOR_NONLOCAL_EXIT ();
DROP ();
if (SCM_VALUESP (*sp))
{
@ -931,6 +934,9 @@ VM_DEFINE_INSTRUCTION (goto_cc, "goto/cc", 0, 1, 1)
POP (proc);
SYNC_ALL ();
cont = scm_make_continuation (&first);
ASSERT (sp == vp->sp);
ASSERT (fp == vp->fp);
ASSERT (ip == vp->ip);
if (first)
{
PUSH (proc);

16
libguile/vm.c
View file

@ -155,6 +155,9 @@ capture_vm_cont (struct scm_vm *vp)
p->stack_base = scm_gc_malloc (p->stack_size * sizeof (SCM),
"capture_vm_cont");
#ifdef VM_ENABLE_STACK_NULLING
if (vp->sp >= vp->stack_base)
if (!vp->sp[0] || vp->sp[1])
abort ();
memset (p->stack_base, 0, p->stack_size * sizeof (SCM));
#endif
p->ip = vp->ip;
@ -178,7 +181,9 @@ reinstate_vm_cont (struct scm_vm *vp, SCM cont)
{
scm_t_ptrdiff nzero = (vp->sp - vp->stack_base) - p->sp;
if (nzero > 0)
memset (vp->stack_base + p->stack_size, 0, nzero);
memset (vp->stack_base + p->stack_size, 0, nzero * sizeof (SCM));
/* actually nzero should always be negative, because vm_reset_stack will
unwind the stack to some point *below* this continuation */
}
#endif
vp->ip = p->ip;
@ -224,12 +229,13 @@ static void
vm_reset_stack (void *data)
{
struct vm_unwind_data *w = data;
struct scm_vm *vp = w->vp;
w->vp->sp = w->sp;
w->vp->fp = w->fp;
w->vp->this_frame = w->this_frame;
vp->sp = w->sp;
vp->fp = w->fp;
vp->this_frame = w->this_frame;
#ifdef VM_ENABLE_STACK_NULLING
memset (w->vp->sp + 1, 0, w->vp->stack_size - (w->vp->sp + 1 - w->vp->stack_base));
memset (vp->sp + 1, 0, (vp->stack_size - (vp->sp + 1 - vp->stack_base)) * sizeof(SCM));
#endif
}