guard: kind of works

rust/ares/src/interpreter.rs

@@ -15,11 +15,12 @@ use crate::noun::{Atom, Cell, IndirectAtom, Noun, Slots, D, T};
 use crate::serf::TERMINATOR;
 use crate::trace::{write_nock_trace, TraceInfo, TraceStack};
 use crate::unifying_equality::unifying_equality;
-use ares_guard::{guard, guard_err};
+use ares_guard::*;
 use ares_macros::tas;
 use assert_no_alloc::{assert_no_alloc, ensure_alloc_counters};
 use bitvec::prelude::{BitSlice, Lsb0};
-use either::Either::*;
+use either::*;
+use std::convert::TryFrom;
 use std::ffi::c_void;
 use std::result;
 use std::sync::atomic::Ordering;
@@ -319,11 +320,25 @@ pub enum Error {
 }
 
 pub enum GuardError {
-    GuardSound = 0,
-    GuardArmor = 1,
-    GuardWeird = 2,
-    GuardSpent = 3,
-    GuardErupt = 4,
+    GuardSound = GUARD_SOUND as isize,
+    GuardArmor = GUARD_ARMOR as isize,
+    GuardWeird = GUARD_WEIRD as isize,
+    GuardSpent = GUARD_SPENT as isize,
+    GuardErupt = GUARD_ERUPT as isize,
+}
+
+impl TryFrom<u32> for GuardError {
+    type Error = ();
+    fn try_from(value: u32) -> std::result::Result<Self, Self::Error> {
+        match value {
+            GUARD_SOUND => Ok(GuardError::GuardSound),
+            GUARD_ARMOR => Ok(GuardError::GuardArmor),
+            GUARD_WEIRD => Ok(GuardError::GuardWeird),
+            GUARD_SPENT => Ok(GuardError::GuardSpent),
+            GUARD_ERUPT => Ok(GuardError::GuardErupt),
+            _ => Err(()),
+        }
+    }
 }
 
 impl Preserve for Error {
@@ -367,48 +382,89 @@ fn debug_assertions(stack: &mut NockStack, noun: Noun) {
     assert_no_junior_pointers!(stack, noun);
 }
 
-extern "C" fn rust_callback(arg: *mut c_void) -> *mut c_void {
-    let closure: &mut Box<dyn FnMut() -> *mut c_void> =
-        unsafe { &mut *(arg as *mut Box<dyn FnMut() -> *mut c_void>) };
-    closure()
+use std::marker::PhantomData;
+
+pub struct CCallback<'closure> {
+    pub function: unsafe extern "C" fn(*mut c_void) -> *mut c_void,
+    pub user_data: *mut c_void,
+
+    // without this it's too easy to accidentally drop the closure too soon
+    _lifetime: PhantomData<&'closure mut c_void>,
 }
 
+impl<'closure> CCallback<'closure> {
+    pub fn new<F>(closure: &'closure mut F) -> Self where F: FnMut() -> Result {
+        let function: unsafe extern "C" fn(*mut c_void) -> *mut c_void = Self::call_closure::<F>;
+
+        debug_assert_eq!(std::mem::size_of::<&'closure mut F>(), std::mem::size_of::<*const c_void>());
+        debug_assert_eq!(std::mem::size_of_val(&function), std::mem::size_of::<*const c_void>());
+
+        Self {
+            function,
+            user_data: closure as *mut F as *mut c_void,
+            _lifetime: PhantomData,
+        }
+    }
+
+    unsafe extern "C" fn call_closure<F>(user_data: *mut c_void) -> *mut c_void where F: FnMut() -> Result {
+        let cb: &mut F = user_data.cast::<F>().as_mut().unwrap();
+        let mut v = (*cb)();
+        let v_ptr = &mut v as *mut _ as *mut c_void;
+        v_ptr
+    }
+}
+
+// fn main() {
+//     let mut v = Vec::new();
+
+//     // must assign to a variable to ensure it lives until the end of scope
+//     let closure = &mut |x: i32| { v.push(x) };
+//     let c = CCallback::new(closure);
+
+//     unsafe { (c.function)(c.user_data, 123) };
+    
+//     assert_eq!(v, [123]);
+// }
+
 pub fn call_with_guard<F: FnMut() -> Result>(
-    f: F,
+    f: &mut F,
     stack: *const *mut c_void,
     alloc: *const *mut c_void,
 ) -> Result {
-    let boxed_f = Box::new(f);
-    let res: Result = Err(Error::Deterministic(D(0)));
-    let mut result = Box::new(res);
-
-    unsafe {
-        let raw_f = Box::into_raw(Box::new(boxed_f));
+    let c = CCallback::new(f);
+    let mut result: Result = Ok(D(0));
     let result_ptr = &mut result as *mut _ as *mut c_void;
 
-        guard(
-            Some(rust_callback),
-            raw_f as *mut c_void,
+    unsafe {
+
+        let err = guard(
+            Some(c.function as unsafe extern "C" fn(*mut c_void) -> *mut c_void),
+            c.user_data as *mut c_void,
             stack,
             alloc,
             result_ptr,
         );
 
-        let _ = Box::from_raw(raw_f);
-
-        if !*result.is_null() {
-            let err = *(result as *const guard_err);
+        if let Ok(err) = GuardError::try_from(err) {
             match err {
-                0 => { // sound
-                    let res = result as *mut Result;
-                    *res
-                },
-                // TODO: handle other errors explicitly.
-                _ => Err(Error::Deterministic(D(0))),
+                GuardError::GuardSound => {
+                    return result;
+                }
+                GuardError::GuardArmor => {
+                    return Err(Error::Deterministic(D(0)));
+                }
+                GuardError::GuardWeird => {
+                    return Err(Error::Deterministic(D(0)));
+                }
+                GuardError::GuardSpent => {
+                    return Err(Error::NonDeterministic(D(0)));
+                }
+                GuardError::GuardErupt => {
+                    return Err(Error::NonDeterministic(D(0)));
                 }
             }
-        else {
-            (Box::from_raw(raw_f))()
+        } else {
+            return Err(Error::Deterministic(D(0)));
         }
     }
 }
@@ -450,8 +506,10 @@ pub fn interpret(context: &mut Context, mut subject: Noun, formula: Noun) -> Res
     // (See https://docs.rs/assert_no_alloc/latest/assert_no_alloc/#advanced-use)
     let nock = assert_no_alloc(|| {
         ensure_alloc_counters(|| {
-            call_with_guard(|| unsafe {
+            let work_closure = &mut || unsafe {
+                eprint!("ares: entered closure\r\n");
                 push_formula(&mut context.stack, formula, true)?;
+                eprint!("ares: pushed formula\r\n");
 
                 loop {
                     let work: NockWork = *context.stack.top();
@@ -989,11 +1047,8 @@ pub fn interpret(context: &mut Context, mut subject: Noun, formula: Noun) -> Res
                         },
                     };
                 }
-            },
-            stack_ptr_ptr,
-            alloc_ptr_ptr,
-            std::ptr::null_mut() as *mut *mut c_void,
-            )
+            };
+            call_with_guard(work_closure, stack_ptr_ptr, alloc_ptr_ptr)
         })
     });
 

rust/ares_guard/c-src/guard.c

@@ -1,4 +1,4 @@
-#include <pthread.h>
+#include <setjmp.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -15,12 +15,13 @@
 static uint64_t *guard_p = 0;
 static uint64_t **stack = 0;
 static uint64_t **alloc = 0;
+static jmp_buf env_buffer;
 
 volatile sig_atomic_t err = guard_sound;
 
-
 // Center the guard page.
-guard_err _focus_guard() {
+guard_err _focus_guard()
+{
   uint64_t *stack_p = *stack;
   uint64_t *alloc_p = *alloc;
 
@@ -61,8 +62,8 @@ guard_err _focus_guard() {
 }
 
 guard_err _slash_guard(void *si_addr) {
-  // fprintf(stderr, "guard: slash at %p\r\n", si_addr);
-  // fprintf(stderr, "guard: guard at %p\r\n", (void *) guard_p);
+  fprintf(stderr, "guard: slash at %p\r\n", si_addr);
+  fprintf(stderr, "guard: guard at %p\r\n", (void *) guard_p);
 
   if (si_addr >= (void *)guard_p && si_addr < (void *)guard_p + GD_PAGESIZE) {
     return _focus_guard();
@@ -71,17 +72,24 @@ guard_err _slash_guard(void *si_addr) {
   return guard_weird;
 }
 
-void _signal_handler(int sig, siginfo_t *si, void *unused) {
+void _signal_handler(int sig, siginfo_t *si, void *unused)
+{
   switch (sig) {
     case SIGSEGV:
+      fprintf(stderr, "guard: sigsegv\r\n");
       err = _slash_guard(si->si_addr);
       break;
     case SIGINT:
+      fprintf(stderr, "guard: sigint\r\n");
       err = guard_erupt;
       break;
     default:
       break;
   }
+
+  if (err != guard_sound) {
+    longjmp(env_buffer, 1);
+  }
 }
 
 guard_err _register_handler() {
@@ -95,18 +103,27 @@ guard_err _register_handler() {
     return guard_weird;
   }
 
+  fprintf(stderr, "guard: registered handler\r\n");
   return guard_sound;
 }
 
-void guard(void *(*f)(void *), void *arg, void *const *stack_pp, void *const *alloc_pp, void *ret) {
+guard_err guard(
+  void *(*f)(void *),
+  void *user_data,
+  void *const *stack_pp,
+  void *const *alloc_pp,
+  void *ret
+)
+{
   stack = (uint64_t**) stack_pp;
   alloc = (uint64_t**) alloc_pp;
 
+  fprintf(stderr, "guard: f pointer at %p\r\n", (void *) f);
   fprintf(stderr, "guard: stack at %p\r\n", (void *) stack);
   fprintf(stderr, "guard: alloc at %p\r\n", (void *) alloc);
-
   fprintf(stderr, "guard: stack pointer at %p\r\n", (void *) *stack);
   fprintf(stderr, "guard: alloc pointer at %p\r\n", (void *) *alloc);
+  fprintf(stderr, "guard: ret pointer at %p\r\n", (void *) ret);
 
   if (guard_p == 0) {
     fprintf(stderr, "guard: installing guard page\r\n");
@@ -124,41 +141,47 @@ void guard(void *(*f)(void *), void *arg, void *const *stack_pp, void *const *al
     goto fail;
   }
 
-  pthread_t thread;
-  int thread_err;
-  thread_err = pthread_create(&thread, NULL, f, arg);
-  if (thread_err != 0) {
-    err = guard_weird;
-    goto fail;
+  void *result;
+  if (setjmp(env_buffer) == 0) {
+    fprintf(stderr, "guard: calling f\r\n");
+    result = f(user_data);
   }
-
-  while (err == guard_sound) {
-    if (pthread_kill(thread, 0) != 0) {
-      goto fail;
-    }
-    sleep(1);
-  }
-
-  void *thread_result;
-  pthread_join(thread, &thread_result);
-  *(void **)ret = thread_result;
-
+  else {
+    fprintf(stderr, "guard: jump buffer already set\r\n");
     if (err != guard_sound) {
+      fprintf(stderr, "guard: not sound\r\n");
       goto fail;
     }
+    else {
+      fprintf(stderr, "guard: assigning ret\r\n");
+      *(void **)ret = result;
+    }
+  }
 
   if (mprotect(guard_p, GD_PAGESIZE, PROT_READ | PROT_WRITE) == -1) {
     err = guard_armor;
     goto fail;
   }
 
-  return;
+  return guard_sound;
 
 fail:
   if (mprotect(guard_p, GD_PAGESIZE, PROT_READ | PROT_WRITE) == -1) {
-    fprintf(stderr, "guard: failed to remove guard page\r\n");
+    fprintf(stderr, "guard: failed to uninstall guard page\r\n");
   }
-  fprintf(stderr, "guard: error %d\r\n", err);
-  *(void **)ret = (void *) &err;
-  return;
+  switch (err) {
+    case guard_armor:
+      fprintf(stderr, "guard: armor error\r\n");
+      break;
+    case guard_weird:
+      fprintf(stderr, "guard: weird error\r\n");
+      break;
+    case guard_spent:
+      fprintf(stderr, "guard: spent error\r\n");
+      break;
+    case guard_erupt:
+      fprintf(stderr, "guard: erupt error\r\n");
+      break;
+  }
+  return err;
 }

rust/ares_guard/c-src/guard.h

@@ -3,6 +3,15 @@
 
 #include <stdint.h>
 
+
+typedef enum {
+  guard_sound = 0, // job's done
+  guard_armor = 1, // mprotect
+  guard_weird = 2, // strange state
+  guard_spent = 3, // out of memory (bail:meme)
+  guard_erupt = 4, // sigint
+} guard_err;
+
 /**
  * Execute the given closure `f` within the memory arena between the
  * `stack` and `alloc` pointers, with guard page protection. Write either
@@ -31,15 +40,13 @@
  * error will be written to the `ret` pointer. The caller is then responsible
  * for handling this error and aborting with a `bail:meme`.
  */
-void guard(void *(*f)(void *), void *arg, void *const *stack_pp, void *const *alloc_pp, void *ret);
-
-typedef enum {
-  guard_sound = 0, // job's done
-  guard_armor = 1, // mprotect
-  guard_weird = 2, // strange state
-  guard_spent = 3, // out of memory (bail:meme)
-  guard_erupt = 4, // sigint
-} guard_err;
+guard_err guard(
+  void *(*f)(void *),
+  void *user_data,
+  void *const *stack_pp,
+  void *const *alloc_pp,
+  void *ret
+);
 
 
 #endif

rust/ares_guard/src/lib.rs

@@ -3,3 +3,9 @@
 #![allow(non_snake_case)]
 
 include!(concat!(env!("OUT_DIR"), "/bindings.rs"));
+
+pub const GUARD_SOUND: u32 = guard_err_guard_sound; 
+pub const GUARD_ARMOR: u32 = guard_err_guard_armor; 
+pub const GUARD_WEIRD: u32 = guard_err_guard_weird;
+pub const GUARD_SPENT: u32 = guard_err_guard_spent;
+pub const GUARD_ERUPT: u32 = guard_err_guard_erupt;