PALSolaris AlignedAllocation feature implementation attempt. (#723)

src/snmalloc/pal/pal_solaris.h

@@ -17,13 +17,49 @@ namespace snmalloc
      * PAL supports.
      *
      */
-    static constexpr uint64_t pal_features = PALPOSIX::pal_features;
+    static constexpr uint64_t pal_features =
+      AlignedAllocation | PALPOSIX::pal_features;
+
+    static constexpr size_t page_size =
+      Aal::aal_name == Sparc ? 0x2000 : 0x1000;
+    static constexpr size_t minimum_alloc_size = page_size;
 
     /**
      * Solaris requires an explicit no-reserve flag in `mmap` to guarantee lazy
      * commit.
      */
     static constexpr int default_mmap_flags = MAP_NORESERVE;
+
+    /**
+     * Reserve memory at a specific alignment.
+     */
+    template<bool state_using>
+    static void* reserve_aligned(size_t size) noexcept
+    {
+      // Alignment must be a power of 2.
+      SNMALLOC_ASSERT(bits::is_pow2(size));
+      SNMALLOC_ASSERT(size >= minimum_alloc_size);
+      UNUSED(state_using);
+
+      uintptr_t alignment =
+        static_cast<uintptr_t>(bits::align_up(size, page_size));
+
+      auto prot =
+        !mitigations(pal_enforce_access) ? PROT_READ | PROT_WRITE : PROT_NONE;
+
+      void* p = mmap(
+        (void*)alignment,
+        size,
+        prot,
+        MAP_PRIVATE | MAP_ANONYMOUS | MAP_ALIGN | default_mmap_flags,
+        -1,
+        0);
+
+      if (p == MAP_FAILED)
+        return nullptr;
+
+      return p;
+    }
   };
 } // namespace snmalloc
 #endif