# HG changeset patch
# User dholmes
# Date 1482267970 18000
# Node ID 285e3f9a1d189a128738829261e9584769972d80
# Parent  3d710f44a7f2e63131d8b755fe0aa0b4ed9f39a9
8170307: Stack size option -Xss is ignored
Reviewed-by: dcubed, sspitsyn, gtriantafill

diff -r 3d710f44a7f2 -r 285e3f9a1d18 src/os/linux/vm/os_linux.cpp
--- a/src/os/linux/vm/os_linux.cpp	Fri Dec 09 19:40:47 2016 +0300
+++ b/src/os/linux/vm/os_linux.cpp	Tue Dec 20 16:06:10 2016 -0500
@@ -1160,33 +1160,30 @@
 
 // Locate initial thread stack. This special handling of initial thread stack
 // is needed because pthread_getattr_np() on most (all?) Linux distros returns
-// bogus value for initial thread.
+// bogus value for the primordial process thread. While the launcher has created
+// the VM in a new thread since JDK 6, we still have to allow for the use of the
+// JNI invocation API from a primordial thread.
 void os::Linux::capture_initial_stack(size_t max_size) {
-  // stack size is the easy part, get it from RLIMIT_STACK
-  size_t stack_size;
+
+  // max_size is either 0 (which means accept OS default for thread stacks) or
+  // a user-specified value known to be at least the minimum needed. If we
+  // are actually on the primordial thread we can make it appear that we have a
+  // smaller max_size stack by inserting the guard pages at that location. But we
+  // cannot do anything to emulate a larger stack than what has been provided by
+  // the OS or threading library. In fact if we try to use a stack greater than
+  // what is set by rlimit then we will crash the hosting process.
+
+  // Maximum stack size is the easy part, get it from RLIMIT_STACK.
+  // If this is "unlimited" then it will be a huge value.
   struct rlimit rlim;
   getrlimit(RLIMIT_STACK, &rlim);
-  stack_size = rlim.rlim_cur;
+  size_t stack_size = rlim.rlim_cur;
 
   // 6308388: a bug in ld.so will relocate its own .data section to the
   //   lower end of primordial stack; reduce ulimit -s value a little bit
   //   so we won't install guard page on ld.so's data section.
   stack_size -= 2 * page_size();
 
-  // 4441425: avoid crash with "unlimited" stack size on SuSE 7.1 or Redhat
-  //   7.1, in both cases we will get 2G in return value.
-  // 4466587: glibc 2.2.x compiled w/o "--enable-kernel=2.4.0" (RH 7.0,
-  //   SuSE 7.2, Debian) can not handle alternate signal stack correctly
-  //   for initial thread if its stack size exceeds 6M. Cap it at 2M,
-  //   in case other parts in glibc still assumes 2M max stack size.
-  // FIXME: alt signal stack is gone, maybe we can relax this constraint?
-#ifndef IA64
-  if (stack_size > 2 * K * K) stack_size = 2 * K * K;
-#else
-  // Problem still exists RH7.2 (IA64 anyway) but 2MB is a little small
-  if (stack_size > 4 * K * K) stack_size = 4 * K * K;
-#endif
-
   // Try to figure out where the stack base (top) is. This is harder.
   //
   // When an application is started, glibc saves the initial stack pointer in
@@ -1346,14 +1343,18 @@
   // stack_top could be partially down the page so align it
   stack_top = align_size_up(stack_top, page_size());
 
-  if (max_size && stack_size > max_size) {
-     _initial_thread_stack_size = max_size;
+  // Allowed stack value is minimum of max_size and what we derived from rlimit
+  if (max_size > 0) {
+    _initial_thread_stack_size = MIN2(max_size, stack_size);
   } else {
-     _initial_thread_stack_size = stack_size;
+    // Accept the rlimit max, but if stack is unlimited then it will be huge, so
+    // clamp it at 8MB as we do on Solaris
+    _initial_thread_stack_size = MIN2(stack_size, 8*M);
   }
 
   _initial_thread_stack_size = align_size_down(_initial_thread_stack_size, page_size());
   _initial_thread_stack_bottom = (address)stack_top - _initial_thread_stack_size;
+  assert(_initial_thread_stack_bottom < (address)stack_top, "overflow!");
 }
 
 ////////////////////////////////////////////////////////////////////////////////