---

yaml
---
r: 188313
b: refs/heads/tmp
c: 243c516
h: refs/heads/master
i:
  188311: f31f80b
v: v3

Author: pnkfelix

[refs]

@@ -34,5 +34,5 @@ refs/heads/building: 126db549b038c84269a1e4fe46f051b2c15d6970
 refs/heads/beta: 522d09dfecbeca1595f25ac58c6d0178bbd21d7d
 refs/heads/windistfix: 7608dbad651f02e837ed05eef3d74a6662a6e928
 refs/tags/1.0.0-alpha: e42bd6d93a1d3433c486200587f8f9e12590a4d7
-refs/heads/tmp: 185c074798ce87429118868c292d2c2c7dc46cfc
+refs/heads/tmp: 243c5164ea32b38c4ac44fdd5e0ceb2da45c283f
 refs/tags/1.0.0-alpha.2: 4c705f6bc559886632d3871b04f58aab093bfa2f

branches/tmp/src/libstd/rt/mod.rs

@@ -27,6 +27,7 @@ use marker::Send;
 use ops::FnOnce;
 use sys;
 use thunk::Thunk;
+use usize;
 
 // Reexport some of our utilities which are expected by other crates.
 pub use self::util::{default_sched_threads, min_stack, running_on_valgrind};
@@ -78,7 +79,20 @@ fn lang_start(main: *const u8, argc: int, argv: *const *const u8) -> int {
     // FIXME #11359 we just assume that this thread has a stack of a
     // certain size, and estimate that there's at most 20KB of stack
     // frames above our current position.
-    let my_stack_bottom = my_stack_top + 20000 - OS_DEFAULT_STACK_ESTIMATE;
+    const TWENTY_KB: uint = 20000;
+
+    // saturating-add to sidestep overflow
+    let top_plus_spill = if usize::MAX - TWENTY_KB < my_stack_top {
+        usize::MAX
+    } else {
+        my_stack_top + TWENTY_KB
+    };
+    // saturating-sub to sidestep underflow
+    let my_stack_bottom = if top_plus_spill < OS_DEFAULT_STACK_ESTIMATE {
+        0
+    } else {
+        top_plus_spill - OS_DEFAULT_STACK_ESTIMATE
+    };
 
     let failed = unsafe {
         // First, make sure we don't trigger any __morestack overflow checks,