ruby · ioquatix · Apr 17, 2025 · Apr 10, 2025 · Apr 16, 2025 · Apr 17, 2025
diff --git a/ext/-test-/stack/extconf.rb b/ext/-test-/stack/extconf.rb
@@ -0,0 +1,3 @@
+# frozen_string_literal: false
+require_relative "../auto_ext.rb"
+auto_ext(inc: true)
diff --git a/ext/-test-/stack/stack.c b/ext/-test-/stack/stack.c
@@ -0,0 +1,24 @@
+#include "ruby.h"
+#include "internal/string.h"
+
+static VALUE
+stack_alloca_overflow(VALUE self)
+{
+    size_t i = 0;
+
+    while (1) {
+        // Allocate and touch memory to force actual stack usage:
+        volatile char *stack = alloca(1024);
+        stack[0] = (char)i;
+        stack[1023] = (char)i;
+        i++;
+    }
+
+    return Qnil;
+}
+
+void
+Init_stack(VALUE klass)
+{
+    rb_define_singleton_method(rb_cThread, "alloca_overflow", stack_alloca_overflow, 0);
+}
diff --git a/test/-ext-/stack/test_stack_overflow.rb b/test/-ext-/stack/test_stack_overflow.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+require 'test/unit'
+
+class Test_StackOverflow < Test::Unit::TestCase
+  def test_proc_overflow
+    omit("Windows stack overflow handling is missing") if RUBY_PLATFORM =~ /mswin|win32|mingw/
+
+    assert_separately([], <<~RUBY)
+      # GC may try to scan the top of the stack and cause a SEGV.
+      GC.disable
+      require '-test-/stack'
+
+      assert_raise(SystemStackError) do
+        Thread.alloca_overflow
+      end
+    RUBY
+  end
+
+  def test_thread_stack_overflow
+    omit("Windows stack overflow handling is missing") if RUBY_PLATFORM =~ /mswin|win32|mingw/
+
+    assert_separately([], <<~RUBY)
+      require '-test-/stack'
+      GC.disable
+
+      thread = Thread.new do
+        Thread.current.report_on_exception = false
+        Thread.alloca_overflow
+      end
+
+      assert_raise(SystemStackError) do
+        thread.join
+      end
+    RUBY
+  end
+
+  def test_fiber_stack_overflow
+    omit("Windows stack overflow handling is missing") if RUBY_PLATFORM =~ /mswin|win32|mingw/
+
+    assert_separately([], <<~RUBY)
+      require '-test-/stack'
+      GC.disable
+
+      fiber = Fiber.new do
+        Thread.alloca_overflow
+      end
+
+      assert_raise(SystemStackError) do
+        fiber.resume
+      end
+    RUBY
+  end
+end
diff --git a/thread_pthread.c b/thread_pthread.c
@@ -3149,8 +3149,12 @@ ruby_stack_overflowed_p(const rb_thread_t *th, const void *addr)
     const size_t water_mark = 1024 * 1024;
     STACK_GROW_DIR_DETECTION;
 
+    if (th) {
+        size = th->ec->machine.stack_maxsize;
+        base = (char *)th->ec->machine.stack_start - STACK_DIR_UPPER(0, size);
+    }
 #ifdef STACKADDR_AVAILABLE
-    if (get_stack(&base, &size) == 0) {
+    else if (get_stack(&base, &size) == 0) {
 # ifdef __APPLE__
         if (pthread_equal(th->nt->thread_id, native_main_thread.id)) {
             struct rlimit rlim;
@@ -3161,15 +3165,11 @@ ruby_stack_overflowed_p(const rb_thread_t *th, const void *addr)
 # endif
         base = (char *)base + STACK_DIR_UPPER(+size, -size);
     }
-    else
 #endif
-    if (th) {
-        size = th->ec->machine.stack_maxsize;
-        base = (char *)th->ec->machine.stack_start - STACK_DIR_UPPER(0, size);
-    }
     else {
         return 0;
     }
+
     size /= RUBY_STACK_SPACE_RATIO;
     if (size > water_mark) size = water_mark;
     if (IS_STACK_DIR_UPPER()) {