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VM never extends vp->sp beyond mapped region of stack

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* libguile/vm-engine.c (ALLOC_FRAME): Fold CHECK_OVERFLOW into this
  routine, and rework to not extend vp->sp until the stack has been
  expanded.

* libguile/vm.c (vm_increase_sp): Likewise, don't extend vp->sp until
  the stack has expanded.
  (vm_expand_stack): Rework to take the new stack pointer as an
  argument, and also to update vp->sp_max_since_gc and vp->sp.
This commit is contained in:
Andy Wingo 2014-02-20 10:17:51 +01:00
parent 7e2fd4e7f5
commit c2ae85beab
2 changed files with 33 additions and 44 deletions
Download patch file Download diff file Expand all files Collapse all files

54
libguile/vm-engine.c
View file

@ -132,19 +132,7 @@
/* Virtual Machine
This is Guile's new virtual machine. When I say "new", I mean
relative to the current virtual machine. At some point it will
become "the" virtual machine, and we'll delete this paragraph. As
such, the rest of the comments speak as if there's only one VM.
In difference from the old VM, local 0 is the procedure, and the
first argument is local 1. At some point in the future we should
change the fp to point to the procedure and not to local 1.
<more overview here>
*/
/* The VM has three state bits: the instruction pointer (IP), the frame
The VM has three state bits: the instruction pointer (IP), the frame
pointer (FP), and the top-of-stack pointer (SP). We cache the first
two of these in machine registers, local to the VM, because they are
used extensively by the VM. As the SP is used more by code outside
@ -173,33 +161,30 @@
} while (0)
/* After advancing vp->sp, but before writing any stack slots, check
that it is actually in bounds. If it is not in bounds, currently we
signal an error. In the future we may expand the stack instead,
possibly by moving it elsewhere, therefore no pointer into the stack
besides FP is valid across a CHECK_OVERFLOW call. Be careful! */
#define CHECK_OVERFLOW() \
do { \
if (SCM_UNLIKELY (vp->sp >= vp->stack_limit)) \
{ \
SYNC_IP (); \
vm_expand_stack (vp); \
CACHE_FP (); \
} \
} while (0)
/* Reserve stack space for a frame. Will check that there is sufficient
stack space for N locals, including the procedure. Invoke after
preparing the new frame and setting the fp and ip. */
preparing the new frame and setting the fp and ip.
If there is not enough space for this frame, we try to expand the
stack, possibly relocating it somewhere else in the address space.
Because of the possible relocation, no pointer into the stack besides
FP is valid across an ALLOC_FRAME call. Be careful! */
#define ALLOC_FRAME(n) \
do { \
vp->sp = LOCAL_ADDRESS (n - 1); \
if (vp->sp > vp->sp_max_since_gc) \
SCM *new_sp = LOCAL_ADDRESS (n - 1); \
if (new_sp > vp->sp_max_since_gc) \
{ \
vp->sp_max_since_gc = vp->sp; \
CHECK_OVERFLOW (); \
if (SCM_UNLIKELY (new_sp >= vp->stack_limit)) \
{ \
SYNC_IP (); \
vm_expand_stack (vp, new_sp); \
CACHE_FP (); \
} \
else \
vp->sp_max_since_gc = vp->sp = new_sp; \
} \
else \
vp->sp = new_sp; \
} while (0)
/* Reset the current frame to hold N locals. Used when we know that no
@ -3235,7 +3220,6 @@ VM_NAME (scm_i_thread *thread, struct scm_vm *vp,
#undef BV_INT_REF
#undef BV_INT_SET
#undef CACHE_REGISTER
#undef CHECK_OVERFLOW
#undef END_DISPATCH_SWITCH
#undef FREE_VARIABLE_REF
#undef INIT

23
libguile/vm.c
View file

@ -64,7 +64,7 @@ static SCM sym_debug;
/* #define VM_ENABLE_PARANOID_ASSERTIONS */
static void vm_expand_stack (struct scm_vm *vp) SCM_NOINLINE;
static void vm_expand_stack (struct scm_vm *vp, SCM *new_sp) SCM_NOINLINE;
/* RESTORE is for the case where we know we have done a PUSH of equal or
greater stack size in the past. Otherwise PUSH is the thing, which
@ -74,13 +74,16 @@ enum vm_increase_sp_kind { VM_SP_PUSH, VM_SP_RESTORE };
static inline void
vm_increase_sp (struct scm_vm *vp, SCM *new_sp, enum vm_increase_sp_kind kind)
{
vp->sp = new_sp;
if (new_sp > vp->sp_max_since_gc)
if (new_sp <= vp->sp_max_since_gc)
{
vp->sp_max_since_gc = new_sp;
if (kind == VM_SP_PUSH && new_sp >= vp->stack_limit)
vm_expand_stack (vp);
vp->sp = new_sp;
return;
}
if (kind == VM_SP_PUSH && new_sp >= vp->stack_limit)
vm_expand_stack (vp, new_sp);
else
vp->sp_max_since_gc = vp->sp = new_sp;
}
static inline void
@ -989,9 +992,9 @@ scm_i_vm_free_stack (struct scm_vm *vp)
}
static void
vm_expand_stack (struct scm_vm *vp)
vm_expand_stack (struct scm_vm *vp, SCM *new_sp)
{
scm_t_ptrdiff stack_size = vp->sp + 1 - vp->stack_base;
scm_t_ptrdiff stack_size = new_sp + 1 - vp->stack_base;
if (stack_size > hard_max_stack_size)
{
@ -1028,7 +1031,6 @@ vm_expand_stack (struct scm_vm *vp)
SCM *fp;
if (vp->fp)
vp->fp += reloc;
vp->sp += reloc;
vp->sp_max_since_gc += reloc;
fp = vp->fp;
while (fp)
@ -1042,6 +1044,8 @@ vm_expand_stack (struct scm_vm *vp)
fp = next_fp;
}
}
new_sp += reloc;
}
if (stack_size >= vp->max_stack_size)
@ -1068,6 +1072,7 @@ vm_expand_stack (struct scm_vm *vp)
}
/* Otherwise continue, with the new enlarged stack. */
vp->sp_max_since_gc = vp->sp = new_sp;
}
static struct scm_vm *