Merge pull request #92 from devnexen/pal_apple_anon_mon

darwin: override zero/non zeroed pages to tag them.

src/pal/pal.h

@@ -27,7 +27,7 @@ namespace snmalloc
 #  if defined(_WIN32)
     PALWindows;
 #  elif defined(__APPLE__)
-    PALApple;
+    PALApple<>;
 #  elif defined(__linux__)
     PALLinux;
 #  elif defined(FreeBSD_KERNEL)

src/pal/pal_apple.h

@@ -3,15 +3,15 @@
 #ifdef __APPLE__
 #  include "pal_bsd.h"
 
+#  include <mach/vm_statistics.h>
+
 namespace snmalloc
 {
   /**
    * PAL implementation for Apple systems (macOS, iOS, watchOS, tvOS...).
-   *
-   * XNU behaves exactly like a generic BSD platform but this class exists
-   * as a place to add XNU-specific behaviour later, if required.
    */
-  class PALApple : public PALBSD<PALApple>
+  template<int PALAnonID = PALAnonDefaultID>
+  class PALApple : public PALBSD<PALApple<>>
   {
   public:
     /**
@@ -22,6 +22,67 @@ namespace snmalloc
      * should add any required features.
      */
     static constexpr uint64_t pal_features = PALBSD::pal_features;
+
+    /**
+     *  OS specific function for zeroing memory with the Apple application
+     *  tag id.
+     *
+     *  See comment below.
+     */
+    template<bool page_aligned = false>
+    void zero(void* p, size_t size)
+    {
+      if (page_aligned || bits::is_aligned_block<OS_PAGE_SIZE>(p, size))
+      {
+        assert(bits::is_aligned_block<OS_PAGE_SIZE>(p, size));
+        void* r = mmap(
+          p,
+          size,
+          PROT_READ | PROT_WRITE,
+          MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED,
+          pal_anon_id,
+          0);
+
+        if (r != MAP_FAILED)
+          return;
+      }
+
+      bzero(p, size);
+    }
+
+    /**
+     * Reserve memory with the Apple application tag id.
+     *
+     * See comment below.
+     */
+    template<bool committed>
+    void* reserve(const size_t* size)
+    {
+      void* p = mmap(
+        nullptr,
+        *size,
+        PROT_READ | PROT_WRITE,
+        MAP_PRIVATE | MAP_ANONYMOUS,
+        pal_anon_id,
+        0);
+
+      if (p == MAP_FAILED)
+        error("Out of memory");
+
+      return p;
+    }
+
+  private:
+    /**
+     * Anonymous page tag ID
+     *
+     * Darwin platform allows to gives an ID to anonymous pages via
+     * the VM_MAKE_TAG's macro, from 240 up to 255 are guaranteed
+     * to be free of usage, however eventually a lower could be taken
+     * (e.g. LLVM sanitizers has 99) so we can monitor their states
+     * via vmmap for instance.
+     */
+    static constexpr int pal_anon_id = VM_MAKE_TAG(PALAnonID);
   };
 } // namespace snmalloc
 #endif

src/pal/pal_consts.h

@@ -48,4 +48,9 @@ namespace snmalloc
      */
     YesZero
   };
+
+  /**
+   * Default Tag ID for the Apple class
+   */
+  static const int PALAnonDefaultID = 241;
 } // namespace snmalloc