8346160: Fix -Wzero-as-null-pointer-constant warnings from explicit casts

Reviewed-by: stefank, dholmes

Author: Kim Barrett

src/hotspot/os/aix/attachListener_aix.cpp

@@ -39,7 +39,7 @@
 #include <unistd.h>
 
 #ifndef UNIX_PATH_MAX
-#define UNIX_PATH_MAX   sizeof(((struct sockaddr_un *)0)->sun_path)
+#define UNIX_PATH_MAX   sizeof(sockaddr_un::sun_path)
 #endif
 
 // The attach mechanism on AIX  uses a UNIX domain socket. An attach listener

src/hotspot/os/posix/attachListener_posix.cpp

@@ -43,7 +43,7 @@
 #ifndef AIX
 
 #ifndef UNIX_PATH_MAX
-#define UNIX_PATH_MAX   sizeof(((struct sockaddr_un *)0)->sun_path)
+#define UNIX_PATH_MAX   sizeof(sockaddr_un::sun_path)
 #endif
 
 // The attach mechanism on Linux and BSD uses a UNIX domain socket. An attach

src/hotspot/os/posix/perfMemory_posix.cpp

@@ -1053,7 +1053,7 @@ static char* mmap_create_shared(size_t size) {
     return nullptr;
   }
 
-  mapAddress = (char*)::mmap((char*)0, size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
+  mapAddress = (char*)::mmap(nullptr, size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
 
   result = ::close(fd);
   assert(result != OS_ERR, "could not close file");
@@ -1208,7 +1208,7 @@ static void mmap_attach_shared(int vmid, char** addr, size_t* sizep, TRAPS) {
 
   assert(size > 0, "unexpected size <= 0");
 
-  char* mapAddress = (char*)::mmap((char*)0, size, mmap_prot, MAP_SHARED, fd, 0);
+  char* mapAddress = (char*)::mmap(nullptr, size, mmap_prot, MAP_SHARED, fd, 0);
 
   int result = ::close(fd);
   assert(result != OS_ERR, "could not close file");

src/hotspot/share/oops/compressedKlass.cpp

@@ -278,7 +278,7 @@ void CompressedKlassPointers::initialize(address addr, size_t len) {
   if (!set_klass_decode_mode()) {
 
     // Give fatal error if this is a specified address
-    if ((address)CompressedClassSpaceBaseAddress == _base) {
+    if (CompressedClassSpaceBaseAddress == (size_t)_base) {
       vm_exit_during_initialization(
             err_msg("CompressedClassSpaceBaseAddress=" PTR_FORMAT " given with shift %d, cannot be used to encode class pointers",
                     CompressedClassSpaceBaseAddress, _shift));

src/hotspot/share/utilities/vmError.cpp

@@ -133,7 +133,7 @@ static const char* env_list[] = {
   // defined on Windows
   "OS", "PROCESSOR_IDENTIFIER", "_ALT_JAVA_HOME_DIR", "TMP", "TEMP",
 
-  (const char *)0
+  nullptr                       // End marker.
 };
 
 // A simple parser for -XX:OnError, usage: