Fixes for __cxa_finalize
* Ability to register atexit handler from atexit handler
* Correct way to handle both forms of atexit handler
Bug: https://code.google.com/p/android/issues/detail?id=66595
Bug: 4998315
Change-Id: I39529afaef97b6e1469c21389d54c0d7d175da28
diff --git a/libc/stdlib/atexit.c b/libc/stdlib/atexit.c
index 4e14434..b051e22 100644
--- a/libc/stdlib/atexit.c
+++ b/libc/stdlib/atexit.c
@@ -41,11 +41,52 @@
struct atexit *__atexit;
/*
+ * TODO: Read this before upstreaming:
+ *
+ * As of Apr 2014 there is a bug regaring function type detection logic in
+ * Free/Open/NetBSD implementations of __cxa_finalize().
+ *
+ * What it is about:
+ * First of all there are two kind of atexit handlers:
+ * 1) void handler(void) - this is the regular type
+ * available for to user via atexit(.) function call.
+ *
+ * 2) void internal_handler(void*) - this is the type
+ * __cxa_atexit() function expects. This handler is used
+ * by C++ compiler to register static destructor calls.
+ * Note that calling this function as the handler of type (1)
+ * results in incorrect this pointer in static d-tors.
+ *
+ * What is wrong with BSD implementations:
+ *
+ * They use dso argument to identify the handler type. The problem
+ * with it is dso is also used to identify the handlers associated
+ * with particular dynamic library and allow __cxa_finalize to call correct
+ * set of functions on dlclose(). And it cannot identify both.
+ *
+ * What is correct way to identify function type?
+ *
+ * Consider this:
+ * 1. __cxa_finalize and __cxa_atexit are part of libc and do not have access to hidden
+ * &__dso_handle.
+ * 2. __cxa_atexit has only 3 arguments: function pointer, function argument, dso.
+ * none of them can be reliably used to pass information about handler type.
+ * 3. following http://www.codesourcery.com/cxx-abi/abi.html#dso-dtor (3.3.5.3 - B)
+ * translation of user atexit -> __cxa_atexit(f, NULL, NULL) results in crashes
+ * on exit() after dlclose() of a library with an atexit() call.
+ *
+ * One way to resolve this is to always call second form of handler, which will
+ * result in storing unused argument in register/stack depending on architecture
+ * and should not present any problems.
+ *
+ * Another way is to make them dso-local in one way or the other.
+ */
+
+/*
* Function pointers are stored in a linked list of pages. The list
* is initially empty, and pages are allocated on demand. The first
* function pointer in the first allocated page (the last one in
* the linked list) was reserved for the cleanup function.
- * TODO: switch to the regular FreeBSD/NetBSD atexit implementation.
*
* Outside the following functions, all pages are mprotect()'ed
* to prevent unintentional/malicious corruption.
@@ -94,7 +135,7 @@
__atexit_invalid = 0;
}
fnp = &p->fns[p->ind++];
- fnp->fn_ptr.cxa_func = func;
+ fnp->cxa_func = func;
fnp->fn_arg = arg;
fnp->fn_dso = dso;
if (mprotect(p, pgsize, PROT_READ))
@@ -113,57 +154,59 @@
void
__cxa_finalize(void *dso)
{
- struct atexit *p, *q;
+ struct atexit *p, *q, *original_atexit;
struct atexit_fn fn;
- int n, pgsize = getpagesize();
+ int n, pgsize = getpagesize(), original_ind;
static int call_depth;
if (__atexit_invalid)
return;
-
_ATEXIT_LOCK();
call_depth++;
- for (p = __atexit; p != NULL; p = p->next) {
- for (n = p->ind; --n >= 0;) {
- if (p->fns[n].fn_ptr.cxa_func == NULL)
- continue; /* already called */
- if (dso != NULL && dso != p->fns[n].fn_dso)
- continue; /* wrong DSO */
-
+ p = original_atexit = __atexit;
+ n = original_ind = p != NULL ? p->ind : 0;
+ while (p != NULL) {
+ if (p->fns[n].cxa_func != NULL /* not called */
+ && (dso == NULL || dso == p->fns[n].fn_dso)) { /* correct DSO */
/*
* Mark handler as having been already called to avoid
* dupes and loops, then call the appropriate function.
*/
fn = p->fns[n];
if (mprotect(p, pgsize, PROT_READ | PROT_WRITE) == 0) {
- p->fns[n].fn_ptr.cxa_func = NULL;
+ p->fns[n].cxa_func = NULL;
mprotect(p, pgsize, PROT_READ);
}
+
_ATEXIT_UNLOCK();
-#if ANDROID
- /* it looks like we should always call the function
- * with an argument, even if dso is not NULL. Otherwise
- * static destructors will not be called properly on
- * the ARM.
- */
- (*fn.fn_ptr.cxa_func)(fn.fn_arg);
-#else /* !ANDROID */
- if (dso != NULL)
- (*fn.fn_ptr.cxa_func)(fn.fn_arg);
- else
- (*fn.fn_ptr.std_func)();
-#endif /* !ANDROID */
+ (*fn.cxa_func)(fn.fn_arg);
_ATEXIT_LOCK();
+ // check for new atexit handlers
+ if ((__atexit->ind != original_ind) || (__atexit != original_atexit)) {
+ // need to restart now to preserve correct
+ // call order - LIFO
+ p = original_atexit = __atexit;
+ n = original_ind = p->ind;
+ continue;
+ }
+ }
+ if (n == 0) {
+ p = p->next;
+ n = p != NULL ? p->ind : 0;
+ } else {
+ --n;
}
}
+ --call_depth;
+
/*
* If called via exit(), unmap the pages since we have now run
* all the handlers. We defer this until calldepth == 0 so that
* we don't unmap things prematurely if called recursively.
*/
- if (dso == NULL && --call_depth == 0) {
+ if (dso == NULL && call_depth == 0) {
for (p = __atexit; p != NULL; ) {
q = p;
p = p->next;