zend_call_stack.c: AIX backend

Uses pthread_getthrds_np (so requires pthread linked, by default on ZTS,
needs to be added for NTS). The stack size part is weird, but works in
testing.

An alternative approach is using procfs, but I didn't bother with this
due to it not working on PASE (and the pthread approach works for the
main thread too).

Author: NattyNarwhal

Zend/Zend.m4

@@ -148,6 +148,7 @@ AC_CHECK_FUNCS(m4_normalize([
   pthread_attr_getstack
   pthread_get_stackaddr_np
   pthread_getattr_np
+  pthread_getthrds_np
   pthread_stackseg_np
   strnlen
 ]))

Zend/zend_call_stack.c

@@ -36,7 +36,8 @@
 #endif /* ZEND_WIN32 */
 #if (defined(HAVE_PTHREAD_GETATTR_NP) && defined(HAVE_PTHREAD_ATTR_GETSTACK)) || \
     defined(__FreeBSD__) || defined(__APPLE__) || defined(__OpenBSD__) || \
-    defined(__NetBSD__) || defined(__DragonFly__) || defined(__sun)
+    defined(__NetBSD__) || defined(__DragonFly__) || defined(__sun) || \
+    defined(_AIX)
 # include <pthread.h>
 #endif
 #if defined(__FreeBSD__) || defined(__DragonFly__)
@@ -788,6 +789,64 @@ static bool zend_call_stack_get_solaris(zend_call_stack *stack)
 }
 #endif /* defined(__sun) */
 
+#if defined(_AIX)
+static bool zend_call_stack_get_aix_pthread(zend_call_stack *stack)
+{
+#ifdef HAVE_PTHREAD_GETTHRDS_NP
+	pthread_t pt = pthread_self();
+	struct __pthrdsinfo thread_info;
+	/* This buffer needs to exist sadly */
+	char reg[256];
+	int regsz = sizeof(reg);
+
+	if (pthread_getthrds_np(&pt, PTHRDSINFO_QUERY_ALL, &thread_info,
+				sizeof(thread_info), &reg, &regsz)) {
+		return false;
+	}
+
+	/*
+	 * The top of the stack (stackend) is not page aligned, there's some
+	 * internal stuff above it. Thankfully, we don't need page alignment.
+	 *
+	 * The size is a little weird. The stacksize field is smaller than
+	 * subtracting the bottom (stackaddr) from the top; it's about 0x888
+	 * to 0x1888 above stackaddr.
+	 *
+	 * A somewhat crude diagram is available here:
+	 * https://www.ibm.com/docs/en/aix/7.2.0?topic=tuning-thread-environment-variables
+	 *
+	 * pthread->pt_stk.st_limit is __pi_stackend,
+	 * above that is internal pthread junk close to the end of page
+	 * pthread->pt_stk.st_base is __pi_stackaddr,
+	 * below that is the red zone
+	 */
+	stack->base = thread_info.__pi_stackend;
+	stack->max_size = thread_info.__pi_stackend - thread_info.__pi_stackaddr;
+	return true;
+#else
+	/* pthread likely not linked in; default NTS build behaviour */
+	return false;
+#endif
+}
+
+static bool zend_call_stack_get_aix(zend_call_stack *stack)
+{
+	/*
+	 * While we could use /proc on AIX (and the implementation basically
+	 * like the Solaris one, as the procfs is similar), it doesn't work on
+	 * PASE. The pthread API works even on the main thread, so we should
+	 * use it when we have pthread linked (always with ZTS, maybe not with
+	 * NTS builds).
+	 */
+	return zend_call_stack_get_aix_pthread(stack);
+}
+#else
+static bool zend_call_stack_get_aix(zend_call_stack *stack)
+{
+	return false;
+}
+#endif /* defined(_AIX) */
+
 /** Get the stack information for the calling thread */
 ZEND_API bool zend_call_stack_get(zend_call_stack *stack)
 {
@@ -823,6 +882,10 @@ ZEND_API bool zend_call_stack_get(zend_call_stack *stack)
 		return true;
 	}
 
+	if (zend_call_stack_get_aix(stack)) {
+		return true;
+	}
+
 	return false;
 }