Add test cases for forced unwinding.

.github/workflows/task.yaml

@@ -10,7 +10,12 @@ env:
   CARGO_TERM_COLOR: always
 
 jobs:
-  mailbox:
+  priority:
     uses: ./.github/workflows/priority.yaml
     secrets:
       cookie: ${{ secrets.cookie }}
+
+  unwind:
+    uses: ./.github/workflows/unwind.yaml
+    secrets:
+      cookie: ${{ secrets.cookie }}

.github/workflows/unwind.yaml

@@ -0,0 +1,67 @@
+name: Run Tests for Task Unwinding
+
+on:
+  workflow_call:
+    secrets:
+      cookie:
+        required: true
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  diverted:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Run test diverted
+        uses: ./.github/workflows/actions/run-test
+        with:
+          cookie: ${{ secrets.cookie }}
+          category: task
+          sub-category: unwind
+          test-name: diverted
+
+  deferred_direct_drop:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Run test deferred_direct_drop
+        uses: ./.github/workflows/actions/run-test
+        with:
+          cookie: ${{ secrets.cookie }}
+          category: task
+          sub-category: unwind
+          test-name: deferred_direct_drop
+
+  deferred_indirect_drop:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Run test deferred_indirect_drop
+        uses: ./.github/workflows/actions/run-test
+        with:
+          cookie: ${{ secrets.cookie }}
+          category: task
+          sub-category: unwind
+          test-name: deferred_indirect_drop
+
+  deferred_nested_drop:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Run test deferred_nested_drop
+        uses: ./.github/workflows/actions/run-test
+        with:
+          cookie: ${{ secrets.cookie }}
+          category: task
+          sub-category: unwind
+          test-name: deferred_nested_drop

Cargo.toml

@@ -117,3 +117,19 @@ path = "examples/tests/sync/semaphore/initialization.rs"
 [[example]]
 name = "test-task-priority-reduce_priority"
 path = "examples/tests/task/priority/reduce_priority.rs"
+
+[[example]]
+name = "test-task-unwind-diverted"
+path = "examples/tests/task/unwind/diverted.rs"
+
+[[example]]
+name = "test-task-unwind-deferred_direct_drop"
+path = "examples/tests/task/unwind/deferred_direct_drop.rs"
+
+[[example]]
+name = "test-task-unwind-deferred_indirect_drop"
+path = "examples/tests/task/unwind/deferred_indirect_drop.rs"
+
+[[example]]
+name = "test-task-unwind-deferred_nested_drop"
+path = "examples/tests/task/unwind/deferred_nested_drop.rs"

examples/tests/task/unwind/deferred_direct_drop.rs

@@ -0,0 +1,88 @@
+//! A deferred forced unwinding should occur when a drop handler function
+//! overflows the call stack of a task that does not enable dynamic stack
+//! extension. 
+
+#![no_std]
+#![no_main]
+
+extern crate alloc;
+use core::{
+    mem::MaybeUninit,
+    sync::atomic::{AtomicUsize, Ordering},
+};
+use hopter::{boot::main, debug::semihosting, hprintln, task};
+
+#[main]
+fn main(_: cortex_m::Peripherals) {
+    task::build()
+        .set_entry(test_task)
+        .deny_dynamic_stack()
+        .set_stack_size(512)
+        .spawn_restartable()
+        .unwrap();
+}
+
+fn test_task() {
+    // A persistent counter.
+    static CNT: AtomicUsize = AtomicUsize::new(0);
+
+    // Every time the task runs we increment it by 1.
+    let cnt = CNT.fetch_add(1, Ordering::SeqCst);
+
+    // When the task is executed for the first time, run the drop function.
+    // Even if this drop function uses a large stack frame and will overflow
+    // the task's stack while dynamic stack extension is not enabled, the
+    // segmented stack runtime should still allow the drop function to proceed
+    // because we cannot initiate an unwinding inside a drop function. A
+    // deferred forced unwinding will be executed after the drop handler
+    // finishes.
+    if cnt == 0 {
+        core::mem::drop(HasDrop);
+    }
+
+    if cnt == 0 {
+        // The task should have been unwound so this print should not be
+        // reachable.
+        hprintln!("Should not print this.");
+    }
+
+    if cnt > 0 {
+        hprintln!("Task successfully restarted after a deferred forced unwinding.");
+        semihosting::terminate(true);
+    } else {
+        semihosting::terminate(false);
+    }
+}
+
+struct HasDrop;
+
+// A drop function that uses a large stack frame.
+impl Drop for HasDrop {
+    #[inline(never)]
+    fn drop(&mut self) {
+        let _padding = StackFramePadding::new();
+        hprintln!("Drop executed.");
+    }
+}
+
+/// A padding that causes large stack frame.
+struct StackFramePadding {
+    _padding: [u8; 1024],
+}
+
+impl StackFramePadding {
+    /// Use volatile write to prevent the compiler from optimizing away the
+    /// padding.
+    fn new() -> Self {
+        let mut padding = MaybeUninit::<[u8; 1024]>::uninit();
+        let mut ptr = unsafe { (*padding.as_mut_ptr()).as_mut_ptr() };
+        for _ in 0..1024 {
+            unsafe {
+                ptr.write_volatile(0);
+                ptr = ptr.offset(1);
+            }
+        }
+        let padding = unsafe { padding.assume_init() };
+        Self { _padding: padding }
+    }
+}

examples/tests/task/unwind/deferred_direct_drop.txt

@@ -0,0 +1,2 @@
+Drop executed.
+Task successfully restarted after a deferred forced unwinding.

examples/tests/task/unwind/deferred_indirect_drop.rs

@@ -0,0 +1,94 @@
+//! A deferred forced unwinding should occur when a drop handler function
+//! is active in the call stack and it further calls a function that overflows
+//! the stack, and when the task does not enable dynamic stack extension.
+
+#![no_std]
+#![no_main]
+
+extern crate alloc;
+use core::{
+    mem::MaybeUninit,
+    sync::atomic::{AtomicUsize, Ordering},
+};
+use hopter::{boot::main, debug::semihosting, hprintln, task};
+
+#[main]
+fn main(_: cortex_m::Peripherals) {
+    task::build()
+        .set_entry(test_task)
+        .deny_dynamic_stack()
+        .set_stack_size(512)
+        .spawn_restartable()
+        .unwrap();
+}
+
+fn test_task() {
+    // A persistent counter.
+    static CNT: AtomicUsize = AtomicUsize::new(0);
+
+    // Every time the task runs we increment it by 1.
+    let cnt = CNT.fetch_add(1, Ordering::SeqCst);
+
+    // When the task is executed for the first time, run the drop function.
+    // Even if this drop function uses a large stack frame and will overflow
+    // the task's stack while dynamic stack extension is not enabled, the
+    // segmented stack runtime should still allow the drop function to proceed
+    // because we cannot initiate an unwinding inside a drop function. A
+    // deferred forced unwinding will be executed after the drop handler
+    // finishes.
+    if cnt == 0 {
+        core::mem::drop(HasDrop);
+    }
+
+    if cnt == 0 {
+        // The task should have been unwound so this print should not be
+        // reachable.
+        hprintln!("Should not print this.");
+    }
+
+    if cnt > 0 {
+        hprintln!("Task successfully restarted after a deferred forced unwinding.");
+        semihosting::terminate(true);
+    } else {
+        semihosting::terminate(false);
+    }
+}
+
+#[inline(never)]
+fn large_func() {
+    let _padding = StackFramePadding::new();
+    hprintln!("Large function executed.");
+}
+
+struct HasDrop;
+
+// A drop function that uses a large stack frame.
+impl Drop for HasDrop {
+    #[inline(never)]
+    fn drop(&mut self) {
+        large_func();
+        hprintln!("Drop executed.");
+    }
+}
+
+/// A padding that causes large stack frame.
+struct StackFramePadding {
+    _padding: [u8; 1024],
+}
+
+impl StackFramePadding {
+    /// Use volatile write to prevent the compiler from optimizing away the
+    /// padding.
+    fn new() -> Self {
+        let mut padding = MaybeUninit::<[u8; 1024]>::uninit();
+        let mut ptr = unsafe { (*padding.as_mut_ptr()).as_mut_ptr() };
+        for _ in 0..1024 {
+            unsafe {
+                ptr.write_volatile(0);
+                ptr = ptr.offset(1);
+            }
+        }
+        let padding = unsafe { padding.assume_init() };
+        Self { _padding: padding }
+    }
+}

examples/tests/task/unwind/deferred_indirect_drop.txt

@@ -0,0 +1,3 @@
+Large function executed.
+Drop executed.
+Task successfully restarted after a deferred forced unwinding.

examples/tests/task/unwind/deferred_nested_drop.rs

@@ -0,0 +1,100 @@
+//! A deferred forced unwinding should occur when a drop handler function
+//! overflows the call stack of a task that does not enable dynamic stack
+//! extension. This test further tests the case where the drop handler is
+//! nested inside another drop handler. The forced unwinding should begin
+//! only after the return of the outmost drop handler finishes.
+
+#![no_std]
+#![no_main]
+
+extern crate alloc;
+use core::{
+    mem::MaybeUninit,
+    sync::atomic::{AtomicUsize, Ordering},
+};
+use hopter::{boot::main, debug::semihosting, hprintln, task};
+
+#[main]
+fn main(_: cortex_m::Peripherals) {
+    task::build()
+        .set_entry(test_task)
+        .deny_dynamic_stack()
+        .set_stack_size(512)
+        .spawn_restartable()
+        .unwrap();
+}
+
+fn test_task() {
+    // A persistent counter.
+    static CNT: AtomicUsize = AtomicUsize::new(0);
+
+    // Every time the task runs we increment it by 1.
+    let cnt = CNT.fetch_add(1, Ordering::SeqCst);
+
+    // When the task is executed for the first time, run the drop function.
+    // Even if this drop function uses a large stack frame and will overflow
+    // the task's stack while dynamic stack extension is not enabled, the
+    // segmented stack runtime should still allow the drop function to proceed
+    // because we cannot initiate an unwinding inside a drop function. A
+    // deferred forced unwinding will be executed after the drop handler
+    // finishes.
+    if cnt == 0 {
+        core::mem::drop(OuterDrop(InnerDrop));
+    }
+
+    if cnt == 0 {
+        // The task should have been unwound so this print should not be
+        // reachable.
+        hprintln!("Should not print this.");
+    }
+
+    if cnt > 0 {
+        hprintln!("Task successfully restarted after a deferred forced unwinding.");
+        semihosting::terminate(true);
+    } else {
+        semihosting::terminate(false);
+    }
+}
+
+struct OuterDrop(InnerDrop);
+
+// Outter drop implicitly also invokes inner drop.
+impl Drop for OuterDrop {
+    #[inline(never)]
+    fn drop(&mut self) {
+        hprintln!("Outter drop executed.");
+    }
+}
+
+struct InnerDrop;
+
+// A drop function that uses a large stack frame.
+impl Drop for InnerDrop {
+    #[inline(never)]
+    fn drop(&mut self) {
+        let _padding = StackFramePadding::new();
+        hprintln!("Inner drop executed.");
+    }
+}
+
+/// A padding that causes large stack frame.
+struct StackFramePadding {
+    _padding: [u8; 1024],
+}
+
+impl StackFramePadding {
+    /// Use volatile write to prevent the compiler from optimizing away the
+    /// padding.
+    fn new() -> Self {
+        let mut padding = MaybeUninit::<[u8; 1024]>::uninit();
+        let mut ptr = unsafe { (*padding.as_mut_ptr()).as_mut_ptr() };
+        for _ in 0..1024 {
+            unsafe {
+                ptr.write_volatile(0);
+                ptr = ptr.offset(1);
+            }
+        }
+        let padding = unsafe { padding.assume_init() };
+        Self { _padding: padding }
+    }
+}

examples/tests/task/unwind/deferred_nested_drop.txt

@@ -0,0 +1,3 @@
+Outter drop executed.
+Inner drop executed.
+Task successfully restarted after a deferred forced unwinding.