Attempt at an Apple PAL.

Totally untested, but now we have macOS CI we can test there...

src/pal/pal.h

@@ -33,6 +33,7 @@ namespace snmalloc
 
 // If simultating OE, then we need the underlying platform
 #if !defined(OPEN_ENCLAVE) || defined(OPEN_ENCLAVE_SIMULATION)
+#  include "pal_apple.h"
 #  include "pal_free_bsd_kernel.h"
 #  include "pal_freebsd.h"
 #  include "pal_linux.h"
@@ -47,6 +48,8 @@ namespace snmalloc
   using DefaultPal =
 #  if defined(_WIN32)
     PALWindows;
+#  elif defined(__APPLE__)
+    PALApple;
 #  elif defined(__linux__)
     PALLinux;
 #  elif defined(FreeBSD_KERNEL)

src/pal/pal_apple.h

@@ -0,0 +1,88 @@
+#pragma once
+
+#ifdef __APPLE__
+#  include "../ds/bits.h"
+#  include "../mem/allocconfig.h"
+
+#  include <pthread.h>
+#  include <stdio.h>
+#  include <strings.h>
+#  include <sys/mman.h>
+
+namespace snmalloc
+{
+  /**
+   * PAL implementation for Apple systems (macOS, iOS, watchOS, tvOS...).
+   */
+  class PALApple
+  {
+  public:
+    /**
+     * Bitmap of PalFeatures flags indicating the optional features that this
+     * PAL supports.
+     */
+    static constexpr uint64_t pal_features = 0;
+    static void error(const char* const str)
+    {
+      puts(str);
+      abort();
+    }
+
+    /// Notify platform that we will not be using these pages
+    void notify_not_using(void* p, size_t size) noexcept
+    {
+      assert(bits::is_aligned_block<OS_PAGE_SIZE>(p, size));
+      madvise(p, size, MADV_FREE);
+    }
+
+    /// Notify platform that we will be using these pages
+    template<ZeroMem zero_mem>
+    void notify_using(void* p, size_t size) noexcept
+    {
+      assert(
+        bits::is_aligned_block<OS_PAGE_SIZE>(p, size) || (zero_mem == NoZero));
+      if constexpr (zero_mem == YesZero)
+        zero(p, size);
+    }
+
+    /// OS specific function for zeroing memory
+    template<bool page_aligned = false>
+    void zero(void* p, size_t size) noexcept
+    {
+      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,
+          -1,
+          0);
+
+        if (r != MAP_FAILED)
+          return;
+      }
+
+      bzero(p, size);
+    }
+
+    template<bool committed>
+    void* reserve(size_t* size) noexcept
+    {
+      void* p = mmap(
+        NULL,
+        *size,
+        PROT_READ | PROT_WRITE,
+        MAP_PRIVATE | MAP_ANONYMOUS,
+        -1,
+        0);
+
+      if (p == MAP_FAILED)
+        error("Out of memory");
+
+      return p;
+    }
+  };
+}
+#endif