--- a/hotspot/src/os/aix/vm/os_aix.cpp	Thu Nov 26 14:19:29 2015 +0400
+++ b/hotspot/src/os/aix/vm/os_aix.cpp	Wed Dec 02 10:17:31 2015 +0100
@@ -2263,8 +2263,12 @@
 
 bool os::pd_commit_memory(char* addr, size_t size, bool exec) {
 
-  assert0(is_aligned_to(addr, os::vm_page_size()));
-  assert0(is_aligned_to(size, os::vm_page_size()));
+  assert(is_aligned_to(addr, os::vm_page_size()),
+    "addr " PTR_FORMAT " not aligned to vm_page_size (" PTR_FORMAT ")",
+    p2i(addr), os::vm_page_size());
+  assert(is_aligned_to(size, os::vm_page_size()),
+    "size " PTR_FORMAT " not aligned to vm_page_size (" PTR_FORMAT ")",
+    size, os::vm_page_size());
 
   vmembk_t* const vmi = vmembk_find(addr);
   assert0(vmi);
@@ -2287,8 +2291,12 @@
 }
 
 bool os::pd_uncommit_memory(char* addr, size_t size) {
-  assert0(is_aligned_to(addr, os::vm_page_size()));
-  assert0(is_aligned_to(size, os::vm_page_size()));
+  assert(is_aligned_to(addr, os::vm_page_size()),
+    "addr " PTR_FORMAT " not aligned to vm_page_size (" PTR_FORMAT ")",
+    p2i(addr), os::vm_page_size());
+  assert(is_aligned_to(size, os::vm_page_size()),
+    "size " PTR_FORMAT " not aligned to vm_page_size (" PTR_FORMAT ")",
+    size, os::vm_page_size());
 
   // Dynamically do different things for mmap/shmat.
   const vmembk_t* const vmi = vmembk_find(addr);
@@ -4299,7 +4307,7 @@
 
   pthread_t tid = pthread_self();
   struct __pthrdsinfo pinfo;
-  char dummy[1]; // We only need this to satisfy the api and to not get E.
+  char dummy[1]; // Just needed to satisfy pthread_getthrds_np.
   int dummy_size = sizeof(dummy);
 
   memset(&pinfo, 0, sizeof(pinfo));
@@ -4320,38 +4328,39 @@
   // Not sure what to do here - I feel inclined to forbid this use case completely.
   guarantee0(pinfo.__pi_stacksize);
 
-  // Note: the pthread stack on AIX seems to look like this:
-  //
-  // ---------------------   real base ? at page border ?
+  // Note: we get three values from pthread_getthrds_np:
+  //       __pi_stackaddr, __pi_stacksize, __pi_stackend
   //
-  //     pthread internal data, like ~2K, see also
-  //     http://publib.boulder.ibm.com/infocenter/pseries/v5r3/index.jsp?topic=/com.ibm.aix.prftungd/doc/prftungd/thread_supp_tun_params.htm
-  //
-  // ---------------------   __pi_stackend - not page aligned, (xxxxF890)
-  //
-  //     stack
-  //      ....
+  // high addr    ---------------------
   //
-  //     stack
-  //
-  // ---------------------   __pi_stackend  - __pi_stacksize
-  //
-  //     padding due to AIX guard pages (?) see AIXTHREAD_GUARDPAGES
-  // ---------------------   __pi_stackaddr  (page aligned if AIXTHREAD_GUARDPAGES > 0)
+  //    |         pthread internal data, like ~2K
+  //    |
+  //    |         ---------------------   __pi_stackend   (usually not page aligned, (xxxxF890))
+  //    |
+  //    |
+  //    |
+  //    |
+  //    |
+  //    |
+  //    |          ---------------------   (__pi_stackend - __pi_stacksize)
+  //    |
+  //    |          padding to align the following AIX guard pages, if enabled.
+  //    |
+  //    V          ---------------------   __pi_stackaddr
   //
-  //   AIX guard pages (?)
+  // low addr      AIX guard pages, if enabled (AIXTHREAD_GUARDPAGES > 0)
   //
 
-  // So, the safe thing to do is to use the area from __pi_stackend to __pi_stackaddr;
-  // __pi_stackend however is almost never page aligned.
-  //
+  address stack_base = (address)(pinfo.__pi_stackend);
+  address stack_low_addr = (address)align_ptr_up(pinfo.__pi_stackaddr,  os::vm_page_size());
+  size_t stack_size = stack_base - stack_low_addr;
 
   if (p_stack_base) {
-    (*p_stack_base) = (address) (pinfo.__pi_stackend);
+    *p_stack_base = stack_base;
   }
 
   if (p_stack_size) {
-    (*p_stack_size) = pinfo.__pi_stackend - pinfo.__pi_stackaddr;
+    *p_stack_size = stack_size;
   }
 
   return true;