xref: /third_party/musl/src/exit/linux/atexit.c

#include <stdlib.h>
#include <stdint.h>
#include <stddef.h>
#include "libc.h"
#include "lock.h"
#include "fork_impl.h"
#include "dynlink.h"
#include "musl_log.h"

#define malloc __libc_malloc
#define calloc __libc_calloc
#define realloc undef
#define free __libc_free

/* Ensure that at least 32 atexit handlers can be registered without malloc */
#define COUNT 32

struct node {
	void (*func)(void *);
	void *arg;
	void *dso;
	struct dso *internal_dso; // the internal dso weekptr, used for dlclose
	struct node *prev;
	struct node *next;
};

static size_t len;                  // the number of nodes currently in use
static size_t capacity;             // the number of available nodes
static struct node builtin[COUNT];  // 32 builtin nodes without malloc
static struct node *tail;           // point to the last node, or NULL
static struct node *head;           // point to the first node

static volatile int lock[1];
volatile int *const __atexit_lockptr = lock;

static int grow()
{
	struct node *nodes;

	if (capacity == 0) {
		nodes = builtin;
		head = nodes;
	} else {
		nodes = malloc(sizeof(struct node) * COUNT);
		if (nodes == NULL) {
			return -1;
		}
	}

	for (size_t i = 0; i < COUNT - 1; i++) {
		nodes[i].next = nodes + (i + 1);
	}
	nodes[COUNT - 1].next = NULL;

	// link new nodes after tail
	if (tail) {
		tail->next = nodes;
	}

	capacity += COUNT;
	return 0;
}

static void append_node(void (*func)(void *), void *arg, void *dso, struct dso *internal_dso) {
	struct node *new_tail;
	if (tail == NULL) {
		new_tail = head;
	} else {
		new_tail = tail->next;
	}

	new_tail->func = func;
	new_tail->arg = arg;
	new_tail->dso = dso;
	new_tail->internal_dso = internal_dso;

	new_tail->prev = tail;
	tail = new_tail;

	len++;
}

static struct node* remove_node(struct node *node) {
	struct node *prev = node->prev;
	if (tail == node) {
		// move back
		tail = prev;
		if (tail == NULL) {
			head = node;
		}
	} else {
		// remove node
		struct node *next = node->next;
		if (next) {
			next->prev = prev;
		}
		if (prev) {
			prev->next = next;
		}

		// insert node after tail
		struct node *tail_next = tail->next;
		node->prev = tail;
		node->next = tail_next;
		tail->next = node;
		if (tail_next) {
			tail_next->prev = node;
		}
	}

	len--;
	return prev;
}

void __funcs_on_exit()
{
	void (*func)(void *), *arg;

	LOCK(lock);
	for (; tail; tail = tail->prev) {
		func = tail->func;
		tail->func = NULL; // Avoid repeated invocation.
		if (func != NULL) {
			arg = tail->arg;
			UNLOCK(lock);
			func(arg);
			LOCK(lock);
		}
	}
	UNLOCK(lock);
}

void __cxa_finalize(void *dso)
{
	void (*func)(void *), *arg;
	struct node *node;

	LOCK(lock);
	for (node = tail; node;) {
		if (dso == node->dso) {
			func = node->func;
			if (func != NULL) {
				arg = node->arg;
				UNLOCK(lock);
				func(arg);
				LOCK(lock);
			}

			node = remove_node(node);
			continue;
		}

		node = node->prev;
	}

	UNLOCK(lock);
}

static void call(void *p);
__attribute__ ((__weak__)) extern void *addr2dso(size_t a);

int __cxa_atexit(void (*func)(void *), void *arg, void *dso)
{
	struct dso *p = NULL;
	LOCK(lock);

#if (defined(FEATURE_ATEXIT_CB_PROTECT))
	if ((func == (void *)call) && (dso == NULL)) {
		if (addr2dso != NULL) {
			p = addr2dso((size_t)arg);
			if (p == NULL) {
				UNLOCK(lock);
				MUSL_LOGE("call atexit with invalid callback ptr=%{public}p", arg);
				return -1;
			}
		}
	}
#endif

	if (len >= capacity) {
		if (grow()) {
			UNLOCK(lock);
			return -1;
		}
	}

	append_node(func, arg, dso, p);

	UNLOCK(lock);
	return 0;
}

static void call(void *p)
{
	if (p != NULL)
		((void (*)(void))(uintptr_t)p)();
}

int atexit(void (*func)(void))
{
	return __cxa_atexit(call, (void *)(uintptr_t)func, 0);
}

int invalidate_exit_funcs(struct dso *p)
{
	struct node *node;

	LOCK(lock);
	for (node = tail; node; node = node->prev) {
		// if found exit callback relative to this dso, and
		if (p == node->internal_dso) {
			if ((node->dso == NULL) && node->func == (void *)call) {
				MUSL_LOGD("invalidate callback ptr=%{public}p when uninstall %{public}s", node->arg, p->name);
				node->arg = NULL;
			}
		}
	}
	UNLOCK(lock);

	return 0;
}