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lang: Check stack depth before accessing elements

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I tested this code by hand, make sure to do the same if changing.
This commit is contained in:
Jookia 2023-07-31 23:07:13 +10:00
parent 183df4494b
commit 75c2a5e8fb
1 changed files with 21 additions and 4 deletions
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25
lang/vm.c
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@ -2,6 +2,7 @@
// Copyright (c) 2023 John Watts and the LuminaSensum contributors
#include "vm.h"
#include "error.h"
#include "object.h"
#include <stddef.h>
#include <stdlib.h>
@ -10,14 +11,16 @@ struct vm_state {
Object *stack;
int stack_base;
int stack_next;
int stack_size;
};
VmState vm_create(void) {
struct vm_state *state = malloc(sizeof(struct vm_state));
Object *stack = malloc(sizeof(Object) * 16);
state->stack = stack;
state->stack_size = 16;
state->stack_base = 0;
state->stack_next = 0;
Object *stack = malloc(sizeof(Object) * state->stack_size);
state->stack = stack;
return (VmState)state;
}
@ -30,7 +33,10 @@ void vm_destroy(VmState *state) {
void vm_stack_set(VmState state, int index, Object obj) {
struct vm_state *priv = (struct vm_state *)state;
Object *stack_pos = &priv->stack[priv->stack_base + index];
int offset = priv->stack_base + index;
abort_if(index < 0, "vm_stack_set: negative value");
abort_if(offset >= priv->stack_next, "vm_stack_set: stack overflow");
Object *stack_pos = &priv->stack[offset];
Object old = *stack_pos;
if (old != NULL) {
object_drop(stack_pos);
@ -40,7 +46,10 @@ void vm_stack_set(VmState state, int index, Object obj) {
Object vm_stack_get(VmState state, int index) {
struct vm_state *priv = (struct vm_state *)state;
Object obj = priv->stack[priv->stack_base + index];
int offset = priv->stack_base + index;
abort_if(index < 0, "vm_stack_get: negative value");
abort_if(offset >= priv->stack_next, "vm_stack_get: stack overflow");
Object obj = priv->stack[offset];
if (obj != NULL) {
object_hold(obj);
}
@ -49,11 +58,19 @@ Object vm_stack_get(VmState state, int index) {
void vm_stack_push(VmState state, Object obj) {
struct vm_state *priv = (struct vm_state *)state;
// stack_next starts at 0, stack_size starts at 1
// Convert stack_size to a max stack offset to compensate
int max_stack = priv->stack_size - 1;
// Check if stack_next is outside the stack before
// writing to it
abort_if(priv->stack_next > max_stack, "vm_stack_push: stack overflow");
priv->stack[priv->stack_next++] = obj;
}
Object vm_stack_pop(VmState state) {
struct vm_state *priv = (struct vm_state *)state;
abort_if(priv->stack_next <= priv->stack_base,
"vm_stack_pop: stack base underflow");
Object obj = priv->stack[--priv->stack_next];
priv->stack[priv->stack_next] = NULL;
return obj;