From 590adc0cc7dd1927d83f9368984ab77c1aab4a1e Mon Sep 17 00:00:00 2001
From: Arnaud Giersch <arnaud.giersch@iut-bm.univ-fcomte.fr>
Date: Fri, 11 Apr 2014 13:37:11 +0200
Subject: [PATCH] Fix comment, and add a runtime warning when stack overflow
 protection is known to be broken.

Also set default value to 0 for contexts/guard_size in this case.
---
 src/simgrid/sg_config.c |  4 ++++
 src/simix/smx_context.c | 22 ++++++++++++++++------
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/src/simgrid/sg_config.c b/src/simgrid/sg_config.c
index ef2a7bbeb0..bd6c7e2ef1 100644
--- a/src/simgrid/sg_config.c
+++ b/src/simgrid/sg_config.c
@@ -696,7 +696,11 @@ void sg_config_init(int *argc, char **argv)
     xbt_cfg_register(&_sg_cfg_set, "contexts/guard_size",
                      "Guard size for contexts stacks in memory pages",
                      xbt_cfgelm_int, 1, 1, _sg_cfg_cb_context_guard_size, NULL);
+#if defined(_XBT_WIN32) || (PTH_STACKGROWTH != -1)
+    xbt_cfg_setdefault_int(_sg_cfg_set, "contexts/guard_size", 0);
+#else
     xbt_cfg_setdefault_int(_sg_cfg_set, "contexts/guard_size", 1);
+#endif
     /* No, it was not set yet (the above setdefault() changed this to 1). */
     smx_context_guard_size_was_set = 0;
 
diff --git a/src/simix/smx_context.c b/src/simix/smx_context.c
index b0d7af6661..f222f62f28 100644
--- a/src/simix/smx_context.c
+++ b/src/simix/smx_context.c
@@ -124,11 +124,21 @@ void *SIMIX_context_stack_new(void)
 {
   void *stack;
 
-  /* FIXME: current code for stack protection assumes that stacks are growing
-   * downward (PTH_STACKGROWTH == -1).  Protected pages need to be but after the
-   * stack when PTH_STACKGROWTH == 1. */
+  /* FIXME: current code for stack overflow protection assumes that stacks are
+   * growing downward (PTH_STACKGROWTH == -1).  Protected pages need to be put
+   * after the stack when PTH_STACKGROWTH == 1. */
 
   if (smx_context_guard_size > 0 && !MC_is_active()) {
+
+#if defined(_XBT_WIN32) || (PTH_STACKGROWTH != -1)
+    static int warned_once = 0;
+    if (!warned_once) {
+      XBT_WARN("Stack overflow protection is known to be broken on your system.  Either you're on Windows or PTH_STACKGROWTH != -1 (current value is %d).",
+               PTH_STACKGROWTH);
+      warned_once = 1;
+    }
+#endif
+
     size_t size = smx_context_stack_size + smx_context_guard_size;
 #ifdef HAVE_MC
     /* Cannot use posix_memalign when HAVE_MC. Align stack by hand, and save the
@@ -136,14 +146,14 @@ void *SIMIX_context_stack_new(void)
     char *alloc = xbt_malloc0(size + xbt_pagesize);
     stack = alloc - ((uintptr_t)alloc & (xbt_pagesize - 1)) + xbt_pagesize;
     *((void **)stack - 1) = alloc;
-#elif !defined(WIN32)
+#elif !defined(_XBT_WIN32)
     if (posix_memalign(&stack, xbt_pagesize, size) != 0)
       xbt_die("Failed to allocate stack.");
 #else
-	stack = _aligned_malloc(size, xbt_pagesize);
+    stack = _aligned_malloc(size, xbt_pagesize);
 #endif
 
-#ifndef WIN32
+#ifndef _XBT_WIN32
     if (mprotect(stack, smx_context_guard_size, PROT_NONE) == -1) {
       XBT_WARN("Failed to protect stack: %s", strerror(errno));
       /* That's not fatal, pursue anyway. */
-- 
2.20.1