Sparc support proposal. (#264)

* Sparc support proposal.

* Tweaks from feedback.
Shift to integer/pointers cast like other archs.
Assembly reworks.
Note apparently reading the register once is sufficient to provoke
a pause in the cpu adding a clobber tough.

Author: devnexen

src/aal/aal.h

@@ -23,6 +23,10 @@
 #  define PLATFORM_IS_POWERPC
 #endif
 
+#if defined(__sparc__)
+#  define PLATFORM_IS_SPARC
+#endif
+
 namespace snmalloc
 {
   /**
@@ -54,6 +58,7 @@ namespace snmalloc
     PowerPC,
     X86,
     X86_SGX,
+    Sparc,
   };
 
   /**
@@ -147,6 +152,8 @@ namespace snmalloc
 #  include "aal_arm.h"
 #elif defined(PLATFORM_IS_POWERPC)
 #  include "aal_powerpc.h"
+#elif defined(PLATFORM_IS_SPARC)
+#  include "aal_sparc.h"
 #endif
 
 namespace snmalloc

src/aal/aal_sparc.h

@@ -0,0 +1,62 @@
+#pragma once
+
+#if defined(__arch64__) // More reliable than __sparc64__
+#  define SNMALLOC_VA_BITS_64
+#else
+#  define SNMALLOC_VA_BITS_32
+#endif
+
+namespace snmalloc
+{
+  /**
+   * Sparc architecture abstraction layer.
+   */
+  class AAL_Sparc
+  {
+  public:
+    /**
+     * Bitmap of AalFeature flags
+     */
+    static constexpr uint64_t aal_features = IntegerPointers;
+
+    static constexpr enum AalName aal_name = Sparc;
+
+#ifdef SNMALLOC_VA_BITS_64
+    /**
+     * Even Ultra-Sparc I supports 8192 and onwards
+     */
+    static constexpr size_t smallest_page_size = 0x2000;
+#else
+    static constexpr size_t smallest_page_size = 0x1000;
+#endif
+
+    /**
+     * On Sparc ideally pause instructions ought to be
+     * optimised per Sparc processor but here a version
+     * as least common denominator to avoid numerous ifdef,
+     * reading Conditions Code Register here
+     */
+    static inline void pause()
+    {
+      __asm__ volatile("rd %%ccr, %%g0" ::: "memory");
+    }
+
+    static inline void prefetch(void* ptr)
+    {
+#ifdef SNMALLOC_VA_BITS_64
+      __asm__ volatile("prefetch [%0], 0" ::"r"(ptr));
+#else
+      UNUSED(ptr);
+#endif
+    }
+
+    static inline uint64_t tick()
+    {
+      uint64_t tick;
+      __asm__ volatile("rd %%asr4, %0" : "=r"(tick));
+      return tick;
+    }
+  };
+
+  using AAL_Arch = AAL_Sparc;
+} // namespace snmalloc

src/pal/pal_linux.h

@@ -26,7 +26,7 @@ namespace snmalloc
     static constexpr uint64_t pal_features = PALPOSIX::pal_features;
 
     static constexpr size_t page_size =
-      Aal::aal_name == PowerPC ? 0x10000 : 0x1000;
+      Aal::aal_name == PowerPC ? 0x10000 : PALPOSIX::page_size;
 
     /**
      * OS specific function for zeroing memory.

src/pal/pal_open_enclave.h

@@ -39,7 +39,7 @@ namespace snmalloc
      */
     static constexpr uint64_t pal_features = 0;
 
-    static constexpr size_t page_size = 0x1000;
+    static constexpr size_t page_size = Aal::smallest_page_size;
 
     [[noreturn]] static void error(const char* const str)
     {

src/pal/pal_posix.h

@@ -98,7 +98,7 @@ namespace snmalloc
      */
     static constexpr uint64_t pal_features = LazyCommit;
 
-    static constexpr size_t page_size = 0x1000;
+    static constexpr size_t page_size = Aal::smallest_page_size;
 
     static void print_stack_trace()
     {