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113 lines
3.3 KiB
C
113 lines
3.3 KiB
C
#ifndef EXEC_STACK_H
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#define EXEC_STACK_H
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#include <stddef.h>
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#include <stdint.h>
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#include <stdlib.h>
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#include <string.h>
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#include "jv_alloc.h"
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/*
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* The stack is a directed forest of variably sized blocks. Each block has a
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* "next" block which is at a higher memory address, or 0 if the block has no
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* "next" block. More than one block may have no "next" block. A block may be
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* the "next" block of more than one other block. Pushed blocks are added at
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* the low-address end of the stack.
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*
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* Stack pointers are negative integers that are offsets relative to "mem_end",
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* the end of the allocated region. The stack "bound" is the stack pointer of
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* the last block that would be able to fit in the currently allocated region.
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* The stack "limit" is the stack pointer of the last block currently in the
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* stack. The stack pointer of the "next" block is stored directly below each
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* block.
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*
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* <- mem_end = 0x100
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* 0xF8 +------------+
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* 0xF0 | |
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* 0xE8 +------------+ <- stack_ptr1 = -0x18
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* 0xE0 next = 0
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* 0xD8 +------------+
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* 0xD0 | |
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* 0xC8 | |
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* 0xC0 +------------+ <- stack_ptr2 = limit = -0x40
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* 0xB8 next = -0x18
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* 0xB0
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* 0xA8 <- bound = -0x58
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* 0xA0
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*/
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struct determine_alignment {
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char x;
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union { int i; double d; uint64_t u64; size_t sz; void* ptr; } u;
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};
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enum {ALIGNMENT = offsetof(struct determine_alignment, u)};
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static size_t align_round_up(size_t sz) {
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return ((sz + (ALIGNMENT - 1)) / ALIGNMENT) * ALIGNMENT;
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}
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typedef int stack_ptr;
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struct stack {
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char* mem_end; // one-past-the-end of allocated region
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stack_ptr bound;
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stack_ptr limit; // 0 - stack is empty
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};
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static void stack_init(struct stack* s) {
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s->mem_end = 0;
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s->bound = ALIGNMENT;
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s->limit = 0;
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}
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static void stack_reset(struct stack* s) {
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assert(s->limit == 0 && "stack freed while not empty");
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char* mem_start = s->mem_end - ( -s->bound + ALIGNMENT);
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free(mem_start);
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stack_init(s);
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}
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static int stack_pop_will_free(struct stack* s, stack_ptr p) {
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return p == s->limit;
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}
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static void* stack_block(struct stack* s, stack_ptr p) {
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return (void*)(s->mem_end + p);
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}
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static stack_ptr* stack_block_next(struct stack* s, stack_ptr p) {
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return &((stack_ptr*)stack_block(s, p))[-1];
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}
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static void stack_reallocate(struct stack* s, size_t sz) {
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int old_mem_length = -(s->bound) + ALIGNMENT;
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char* old_mem_start = s->mem_end - old_mem_length;
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int new_mem_length = align_round_up((old_mem_length + sz + 256) * 2);
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char* new_mem_start = jv_mem_realloc(old_mem_start, new_mem_length);
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memmove(new_mem_start + (new_mem_length - old_mem_length),
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new_mem_start, old_mem_length);
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s->mem_end = new_mem_start + new_mem_length;
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s->bound = -(new_mem_length - ALIGNMENT);
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}
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static stack_ptr stack_push_block(struct stack* s, stack_ptr p, size_t sz) {
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int alloc_sz = align_round_up(sz) + ALIGNMENT;
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stack_ptr r = s->limit - alloc_sz;
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if (r < s->bound) {
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stack_reallocate(s, alloc_sz);
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}
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s->limit = r;
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*stack_block_next(s, r) = p;
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return r;
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}
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static stack_ptr stack_pop_block(struct stack* s, stack_ptr p, size_t sz) {
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stack_ptr r = *stack_block_next(s, p);
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if (p == s->limit) {
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int alloc_sz = align_round_up(sz) + ALIGNMENT;
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s->limit += alloc_sz;
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}
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return r;
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}
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#endif
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