move 32 bit heap hint on sunos

src/platform-posix.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 105 matching lines @@
 #if V8_TARGET_ARCH_X64
     uint64_t rnd1 = V8::RandomPrivate(isolate);
     uint64_t rnd2 = V8::RandomPrivate(isolate);
     uint64_t raw_addr = (rnd1 << 32) ^ rnd2;
     // Currently available CPUs have 48 bits of virtual addressing.  Truncate
     // the hint address to 46 bits to give the kernel a fighting chance of
     // fulfilling our placement request.
     raw_addr &= V8_UINT64_C(0x3ffffffff000);
 #else
     uint32_t raw_addr = V8::RandomPrivate(isolate);
+
+    raw_addr &= 0x3ffff000;
+
+# ifdef __sun
+    // For our Solaris/illumos mmap hint, we pick a random address in the bottom
+    // half of the top half of the address space (that is, the third quarter).
+    // Because we do not MAP_FIXED, this will be treated only as a hint -- the
+    // system will not fail to mmap() because something else happens to already
+    // be mapped at our random address. We deliberately set the hint high enough
+    // to get well above the system's break (that is, the heap); Solaris and
+    // illumos will try the hint and if that fails allocate as if there were
+    // no hint at all. The high hint prevents the break from getting hemmed in
+    // at low values, ceding half of the address space to the system heap.
+    raw_addr += 0x80000000;
+# else
     // The range 0x20000000 - 0x60000000 is relatively unpopulated across a
     // variety of ASLR modes (PAE kernel, NX compat mode, etc) and on macos
     // 10.6 and 10.7.
-    raw_addr &= 0x3ffff000;
     raw_addr += 0x20000000;
+# endif
 #endif
     return reinterpret_cast<void*>(raw_addr);
   }
   return NULL;
 }
 
 
 // ----------------------------------------------------------------------------
 // Math functions
 
@@ skipping 508 matching lines @@
   return ntohl(value);
 }
 
 
 Socket* OS::CreateSocket() {
   return new POSIXSocket();
 }
 
 
 } }  // namespace v8::internal