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Avoid undefined pointer difference behavior.

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Fix #458.
This commit is contained in:
Bob Nystrom
2017-10-08 09:42:35 -07:00
parent eba0b97aa2
commit fec54d5021
1 changed files with 10 additions and 8 deletions
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18
src/vm/wren_value.c
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@ -194,22 +194,24 @@ void wrenEnsureStack(WrenVM* vm, ObjFiber* fiber, int needed)
sizeof(Value) * capacity);
fiber->stackCapacity = capacity;
// If the reallocation moves the stack, then we need to shift every pointer
// into the stack to point to its new location.
// If the reallocation moves the stack, then we need to recalculate every
// pointer that points into the old stack to into the same relative distance
// in the new stack. We have to be a little careful about how these are
// calculated because pointer subtraction is only well-defined within a
// single array, hence the slightly redundant-looking arithmetic below.
if (fiber->stack != oldStack)
{
// Top of the stack.
long offset = fiber->stack - oldStack;
if (vm->apiStack >= oldStack && vm->apiStack <= fiber->stackTop)
{
vm->apiStack += offset;
vm->apiStack = fiber->stack + (vm->apiStack - oldStack);
}
// Stack pointer for each call frame.
for (int i = 0; i < fiber->numFrames; i++)
{
fiber->frames[i].stackStart += offset;
CallFrame* frame = &fiber->frames[i];
frame->stackStart = fiber->stack + (frame->stackStart - oldStack);
}
// Open upvalues.
@ -217,10 +219,10 @@ void wrenEnsureStack(WrenVM* vm, ObjFiber* fiber, int needed)
upvalue != NULL;
upvalue = upvalue->next)
{
upvalue->value += offset;
upvalue->value = fiber->stack + (upvalue->value - oldStack);
}
fiber->stackTop += offset;
fiber->stackTop = fiber->stack + (fiber->stackTop - oldStack);
}
}