From 24ae5d704ee6b01d61c148dedc45e31acafbc571 Mon Sep 17 00:00:00 2001
From: David Carlier <devnexen@gmail.com>
Date: Mon, 26 Aug 2019 18:57:45 +0100
Subject: [PATCH] darwin: override zero/non zeroed pages to tag them.

---
 src/pal/pal_apple.h | 50 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/src/pal/pal_apple.h b/src/pal/pal_apple.h
index cc9a96d..d2d6049 100644
--- a/src/pal/pal_apple.h
+++ b/src/pal/pal_apple.h
@@ -22,6 +22,56 @@ namespace snmalloc
      * should add any required features.
      */
     static constexpr uint64_t pal_features = PALBSD::pal_features;
+
+     // OS specific function for zeroing memory with ID 241.
+    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 ID 241.
+    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
+     * 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.
+     */
+    int pal_anon_id = 241 << 24;
   };
 } // namespace snmalloc
 #endif