Support panicking and make unsupported platforms a nop

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "stacker"
-version = "0.1.3"
+version = "0.1.4"
 authors = ["Alex Crichton <alex@alexcrichton.com>"]
 build = "build.rs"
 license = "MIT/Apache-2.0"

build.rs

@@ -14,9 +14,6 @@ fn main() {
         cfg.define("APPLE", None);
     } else if target.contains("windows") {
         cfg.define("WINDOWS", None);
-    } else {
-        panic!("\n\nusing currently unsupported target triple with \
-                stacker: {}\n\n", target);
     }
 
     if target.starts_with("x86_64") {
@@ -26,8 +23,8 @@ fn main() {
         cfg.file(if msvc {"src/arch/i686.asm"} else {"src/arch/i686.S"});
         cfg.define("X86", None);
     } else {
-        panic!("\n\nusing currently unsupported target triple with \
-                stacker: {}\n\n", target);
+        println!("cargo:rustc-cfg=fallback");
+        return;
     }
 
     cfg.include("src/arch").compile("libstacker.a");

src/arch/fallback.rs

@@ -0,0 +1,16 @@
+#[no_mangle]
+extern fn __stacker_stack_pointer() -> usize {
+    panic!("not supported")
+}
+
+#[no_mangle]
+unsafe extern fn __stacker_switch_stacks(
+    _new_stack: usize,
+    _fnptr: unsafe fn(&mut &mut FnMut()),
+    _dataptr: &mut &mut FnMut(),
+) {
+    panic!("not supported")
+}
+
+#[no_mangle]
+extern fn __stacker_black_box(_: *const u8) {}

src/lib.rs

@@ -21,6 +21,11 @@
 //!     // guaranteed to have at least 32K of stack
 //! });
 //! ```
+//!
+//! # Platform support
+//!
+//! Only Windows, MacOS and Linux are supported. Other platforms don't do anything
+//! and will overflow your stack.
 
 #![allow(improper_ctypes)]
 
@@ -30,6 +35,10 @@ extern crate libc;
 
 use std::cell::Cell;
 
+#[cfg(fallback)]
+#[path="arch/fallback.rs"]
+mod fallback;
+
 extern {
     fn __stacker_stack_pointer() -> usize;
     fn __stacker_switch_stacks(new_stack: usize,
@@ -38,17 +47,17 @@ extern {
 }
 
 thread_local! {
-    static STACK_LIMIT: Cell<usize> = Cell::new(unsafe {
+    static STACK_LIMIT: Cell<Option<usize>> = Cell::new(unsafe {
         guess_os_stack_limit()
     })
 }
 
-fn get_stack_limit() -> usize {
+fn get_stack_limit() -> Option<usize> {
     STACK_LIMIT.with(|s| s.get())
 }
 
 fn set_stack_limit(l: usize) {
-    STACK_LIMIT.with(|s| s.set(l))
+    STACK_LIMIT.with(|s| s.set(Some(l)))
 }
 
 /// Grows the call stack if necessary.
@@ -60,49 +69,52 @@ fn set_stack_limit(l: usize) {
 ///
 /// The closure `f` is guaranteed to run on a stack with at least `red_zone`
 /// bytes, and it will be run on the current stack if there's space available.
-pub fn maybe_grow<R, F: FnOnce() -> R>(red_zone: usize,
-                                       stack_size: usize,
-                                       f: F) -> R {
-    if remaining_stack() >= red_zone {
-        f()
+pub fn maybe_grow<R, F: FnOnce() -> R>(red_zone: usize, stack_size: usize, f: F) -> R {
+    if let Some(remaining_stack_bytes) = remaining_stack() {
+        if remaining_stack_bytes >= red_zone {
+            f()
+        } else {
+            grow_the_stack(stack_size, f, remaining_stack_bytes)
+        }
     } else {
-        grow_the_stack(stack_size, f)
+        f()
     }
 }
 
 /// Queries the amount of remaining stack as interpreted by this library.
 ///
 /// This function will return the amount of stack space left which will be used
 /// to determine whether a stack switch should be made or not.
-pub fn remaining_stack() -> usize {
-    unsafe {
-        __stacker_stack_pointer() - get_stack_limit()
-    }
+pub fn remaining_stack() -> Option<usize> {
+    get_stack_limit().map(|limit| unsafe {
+        __stacker_stack_pointer() - limit
+    })
 }
 
 #[inline(never)]
-fn grow_the_stack<R, F: FnOnce() -> R>(stack_size: usize, f: F) -> R {
+fn grow_the_stack<R, F: FnOnce() -> R>(stack_size: usize, f: F, remaining_stack_bytes: usize) -> R {
     let mut f = Some(f);
     let mut ret = None;
     unsafe {
-        _grow_the_stack(stack_size, &mut || {
-            ret = Some(f.take().unwrap()());
+        _grow_the_stack(stack_size, remaining_stack_bytes, &mut || {
+            let f: F = f.take().unwrap();
+            ret = Some(std::panic::catch_unwind(std::panic::AssertUnwindSafe(f)));
         });
     }
-    ret.unwrap()
+    match ret.unwrap() {
+        Ok(ret) => ret,
+        Err(payload) => std::panic::resume_unwind(payload),
+    }
 }
 
-unsafe fn _grow_the_stack(stack_size: usize, mut f: &mut FnMut()) {
+unsafe fn _grow_the_stack(stack_size: usize, old_limit: usize, mut f: &mut FnMut()) {
     // Align to 16-bytes (see below for why)
     let stack_size = (stack_size + 15) / 16 * 16;
 
     // Allocate some new stack for oureslves
     let mut stack = Vec::<u8>::with_capacity(stack_size);
     let new_limit = stack.as_ptr() as usize + 32 * 1024;
 
-    // Save off the old stack limits
-    let old_limit = get_stack_limit();
-
     // Prepare stack limits for the stack switch
     set_stack_limit(new_limit);
 
@@ -135,7 +147,7 @@ cfg_if! {
         //
         // https://github.com/adobe/webkit/blob/0441266/Source/WTF/wtf
         //                   /StackBounds.cpp
-        unsafe fn guess_os_stack_limit() -> usize {
+        unsafe fn guess_os_stack_limit() -> Option<usize> {
             #[cfg(target_pointer_width = "32")]
             extern {
                 #[link_name = "__stacker_get_tib_32"]
@@ -151,12 +163,12 @@ cfg_if! {
             // the struct layout of the 32-bit TIB. It looks like the struct
             // layout of the 64-bit TIB is also the same for getting the stack
             // limit: http://doxygen.reactos.org/d3/db0/structNT__TIB64.html
-            *get_tib_address().offset(2)
+            Some(*get_tib_address().offset(2))
         }
     } else if #[cfg(target_os = "linux")] {
         use std::mem;
 
-        unsafe fn guess_os_stack_limit() -> usize {
+        unsafe fn guess_os_stack_limit() -> Option<usize> {
             let mut attr: libc::pthread_attr_t = mem::zeroed();
             assert_eq!(libc::pthread_attr_init(&mut attr), 0);
             assert_eq!(libc::pthread_getattr_np(libc::pthread_self(),
@@ -166,18 +178,18 @@ cfg_if! {
             assert_eq!(libc::pthread_attr_getstack(&attr, &mut stackaddr,
                                                    &mut stacksize), 0);
             assert_eq!(libc::pthread_attr_destroy(&mut attr), 0);
-            stackaddr as usize
+            Some(stackaddr as usize)
         }
     } else if #[cfg(target_os = "macos")] {
         use libc::{c_void, pthread_t, size_t};
 
-        unsafe fn guess_os_stack_limit() -> usize {
-            libc::pthread_get_stackaddr_np(libc::pthread_self()) as usize -
-                libc::pthread_get_stacksize_np(libc::pthread_self()) as usize
+        unsafe fn guess_os_stack_limit() -> Option<usize> {
+            Some(libc::pthread_get_stackaddr_np(libc::pthread_self()) as usize -
+                libc::pthread_get_stacksize_np(libc::pthread_self()) as usize)
         }
     } else {
-        unsafe fn guess_os_stack_limit() -> usize {
-            panic!("cannot guess the stack limit on this platform");
+        unsafe fn guess_os_stack_limit() -> Option<usize> {
+            None
         }
     }
 }

tests/panic_handling.rs

@@ -0,0 +1,27 @@
+extern crate stacker;
+
+const RED_ZONE: usize = 100*1024; // 100k
+const STACK_PER_RECURSION: usize = 1 * 1024 * 1024; // 1MB
+
+pub fn ensure_sufficient_stack<R, F: FnOnce() -> R + std::panic::UnwindSafe>(
+    f: F
+) -> R {
+    stacker::maybe_grow(RED_ZONE, STACK_PER_RECURSION, f)
+}
+
+#[inline(never)]
+fn recurse(n: usize) {
+    let x = [42u8; 50000];
+    if n == 0 {
+        panic!("an inconvenient time");
+    } else {
+        ensure_sufficient_stack(|| recurse(n - 1));
+    }
+    drop(x);
+}
+
+#[test]
+#[should_panic]
+fn foo() {
+    recurse(10000);
+}