---

yaml
---
r: 188112
b: refs/heads/auto
c: 243c516
h: refs/heads/master
v: v3

Author: pnkfelix

[refs]

@@ -10,7 +10,7 @@ refs/tags/release-0.3: b5f0d0f648d9a6153664837026ba1be43d3e2503
 refs/tags/release-0.3.1: 495bae036dfe5ec6ceafd3312b4dca48741e845b
 refs/tags/release-0.4: e828ea2080499553b97dfe33b3f4d472b4562ad7
 refs/tags/release-0.5: 7e3bcfbf21278251ee936ad53e92e9b719702d73
-refs/heads/auto: 185c074798ce87429118868c292d2c2c7dc46cfc
+refs/heads/auto: 243c5164ea32b38c4ac44fdd5e0ceb2da45c283f
 refs/heads/servo: af82457af293e2a842ba6b7759b70288da276167
 refs/tags/release-0.6: b4ebcfa1812664df5e142f0134a5faea3918544c
 refs/tags/0.1: b19db808c2793fe2976759b85a355c3ad8c8b336

branches/auto/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,