From 4e3033f2122d773c173b0bb50120099589adcf3c Mon Sep 17 00:00:00 2001
From: Kim Barrett <kbarrett@openjdk.org>
Date: Wed, 11 Feb 2026 00:59:20 +0000
Subject: [PATCH] 8332189: Enable -Wzero-as-null-pointer-constant for gcc/clang

Reviewed-by: azafari, dholmes, erikj
---
 doc/hotspot-style.html        |  5 ++--
 doc/hotspot-style.md          |  3 +--
 make/autoconf/flags-cflags.m4 | 47 +++++++++++++++++++----------------
 3 files changed, 28 insertions(+), 27 deletions(-)

diff --git a/doc/hotspot-style.html b/doc/hotspot-style.html
index 362245cd00a..c7126622c7d 100644
--- a/doc/hotspot-style.html
+++ b/doc/hotspot-style.html
@@ -965,9 +965,8 @@ rather than <code>NULL</code>. See the paper for reasons to avoid
 <code>NULL</code>.</p>
 <p>Don't use (constant expression or literal) 0 for pointers. Note that
 C++14 removed non-literal 0 constants from <em>null pointer
-constants</em>, though some compilers continue to treat them as such.
-For historical reasons there may be lingering uses of 0 as a
-pointer.</p>
+constants</em>, though some compilers continue to treat them as
+such.</p>
 <h3 id="atomic">&lt;atomic&gt;</h3>
 <p>Do not use facilities provided by the <code>&lt;atomic&gt;</code>
 header (<a
diff --git a/doc/hotspot-style.md b/doc/hotspot-style.md
index 26549e3ca02..a1ee0403632 100644
--- a/doc/hotspot-style.md
+++ b/doc/hotspot-style.md
@@ -884,8 +884,7 @@ rather than `NULL`.  See the paper for reasons to avoid `NULL`.
 
 Don't use (constant expression or literal) 0 for pointers.  Note that C++14
 removed non-literal 0 constants from _null pointer constants_, though some
-compilers continue to treat them as such.  For historical reasons there may be
-lingering uses of 0 as a pointer.
+compilers continue to treat them as such.
 
 ### &lt;atomic&gt;
 
diff --git a/make/autoconf/flags-cflags.m4 b/make/autoconf/flags-cflags.m4
index 639c3852212..0cdf02c61c6 100644
--- a/make/autoconf/flags-cflags.m4
+++ b/make/autoconf/flags-cflags.m4
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2011, 2025, Oracle and/or its affiliates. All rights reserved.
+# Copyright (c) 2011, 2026, Oracle and/or its affiliates. All rights reserved.
 # DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 #
 # This code is free software; you can redistribute it and/or modify it
@@ -209,7 +209,10 @@ AC_DEFUN([FLAGS_SETUP_WARNINGS],
       BUILD_CC_DISABLE_WARNING_PREFIX="-wd"
       CFLAGS_WARNINGS_ARE_ERRORS="-WX"
 
-      WARNINGS_ENABLE_ALL="-W3"
+      WARNINGS_ENABLE_ALL_NORMAL="-W3"
+      WARNINGS_ENABLE_ADDITIONAL=""
+      WARNINGS_ENABLE_ADDITIONAL_CXX=""
+      WARNINGS_ENABLE_ADDITIONAL_JVM=""
       DISABLED_WARNINGS="4800 5105"
       ;;
 
@@ -218,14 +221,16 @@ AC_DEFUN([FLAGS_SETUP_WARNINGS],
       BUILD_CC_DISABLE_WARNING_PREFIX="-Wno-"
       CFLAGS_WARNINGS_ARE_ERRORS="-Werror"
 
+      WARNINGS_ENABLE_ALL_NORMAL="-Wall -Wextra"
+
       # Additional warnings that are not activated by -Wall and -Wextra
-      WARNINGS_ENABLE_ADDITIONAL="-Winvalid-pch -Wpointer-arith -Wreturn-type \
+      WARNINGS_ENABLE_ADDITIONAL="-Wformat=2 \
+          -Winvalid-pch -Wpointer-arith -Wreturn-type \
           -Wsign-compare -Wtrampolines -Wtype-limits -Wundef -Wuninitialized \
           -Wunused-const-variable=1 -Wunused-function -Wunused-result \
           -Wunused-value"
       WARNINGS_ENABLE_ADDITIONAL_CXX="-Woverloaded-virtual -Wreorder"
-      WARNINGS_ENABLE_ALL_CFLAGS="-Wall -Wextra -Wformat=2 $WARNINGS_ENABLE_ADDITIONAL"
-      WARNINGS_ENABLE_ALL_CXXFLAGS="$WARNINGS_ENABLE_ALL_CFLAGS $WARNINGS_ENABLE_ADDITIONAL_CXX"
+      WARNINGS_ENABLE_ADDITIONAL_JVM="-Wzero-as-null-pointer-constant"
 
       # These warnings will never be turned on, since they generate too many
       # false positives.
@@ -241,16 +246,24 @@ AC_DEFUN([FLAGS_SETUP_WARNINGS],
       BUILD_CC_DISABLE_WARNING_PREFIX="-Wno-"
       CFLAGS_WARNINGS_ARE_ERRORS="-Werror"
 
+      WARNINGS_ENABLE_ALL_NORMAL="-Wall -Wextra"
+
       # Additional warnings that are not activated by -Wall and -Wextra
-      WARNINGS_ENABLE_ADDITIONAL="-Wpointer-arith -Wsign-compare -Wreorder \
+      WARNINGS_ENABLE_ADDITIONAL="-Wformat=2 \
+          -Wpointer-arith -Wsign-compare -Wreorder \
           -Wunused-function -Wundef -Wunused-value -Woverloaded-virtual"
-      WARNINGS_ENABLE_ALL="-Wall -Wextra -Wformat=2 $WARNINGS_ENABLE_ADDITIONAL"
+      WARNINGS_ENABLE_ADDITIONAL_CXX=""
+      WARNINGS_ENABLE_ADDITIONAL_JVM="-Wzero-as-null-pointer-constant"
 
       # These warnings will never be turned on, since they generate too many
       # false positives.
       DISABLED_WARNINGS="unknown-warning-option unused-parameter"
       ;;
   esac
+  WARNINGS_ENABLE_ALL="$WARNINGS_ENABLE_ALL_NORMAL $WARNINGS_ENABLE_ADDITIONAL"
+  WARNINGS_ENABLE_ALL_CXX="$WARNINGS_ENABLE_ALL $WARNINGS_ENABLE_ADDITIONAL_CXX"
+  WARNINGS_ENABLE_ALL_JVM="$WARNINGS_ENABLE_ALL_CXX $WARNINGS_ENABLE_ADDITIONAL_JVM"
+
   AC_SUBST(DISABLE_WARNING_PREFIX)
   AC_SUBST(BUILD_CC_DISABLE_WARNING_PREFIX)
   AC_SUBST(CFLAGS_WARNINGS_ARE_ERRORS)
@@ -604,19 +617,9 @@ AC_DEFUN([FLAGS_SETUP_CFLAGS_HELPER],
   ADLC_LANGSTD_CXXFLAGS="$LANGSTD_CXXFLAGS"
 
   # CFLAGS WARNINGS STUFF
-  # Set JVM_CFLAGS warning handling
-  if test "x$TOOLCHAIN_TYPE" = xgcc; then
-    WARNING_CFLAGS_JDK_CONLY="$WARNINGS_ENABLE_ALL_CFLAGS"
-    WARNING_CFLAGS_JDK_CXXONLY="$WARNINGS_ENABLE_ALL_CXXFLAGS"
-    WARNING_CFLAGS_JVM="$WARNINGS_ENABLE_ALL_CXXFLAGS"
-
-  elif test "x$TOOLCHAIN_TYPE" = xclang; then
-    WARNING_CFLAGS="$WARNINGS_ENABLE_ALL"
-
-  elif test "x$TOOLCHAIN_TYPE" = xmicrosoft; then
-    WARNING_CFLAGS="$WARNINGS_ENABLE_ALL"
-
-  fi
+  WARNING_CFLAGS_JDK_CONLY="$WARNINGS_ENABLE_ALL"
+  WARNING_CFLAGS_JDK_CXXONLY="$WARNINGS_ENABLE_ALL_CXX"
+  WARNING_CFLAGS_JVM="$WARNINGS_ENABLE_ALL_JVM"
 
   # Set some additional per-OS defines.
 
@@ -878,12 +881,12 @@ AC_DEFUN([FLAGS_SETUP_CFLAGS_CPU_DEP],
   CFLAGS_JVM_COMMON="$ALWAYS_CFLAGS_JVM $ALWAYS_DEFINES_JVM \
       $TOOLCHAIN_CFLAGS_JVM ${$1_TOOLCHAIN_CFLAGS_JVM} \
       $OS_CFLAGS $OS_CFLAGS_JVM $CFLAGS_OS_DEF_JVM $DEBUG_CFLAGS_JVM \
-      $WARNING_CFLAGS $WARNING_CFLAGS_JVM $JVM_PICFLAG $FILE_MACRO_CFLAGS \
+      $WARNING_CFLAGS_JVM $JVM_PICFLAG $FILE_MACRO_CFLAGS \
       $REPRODUCIBLE_CFLAGS $BRANCH_PROTECTION_CFLAGS"
 
   CFLAGS_JDK_COMMON="$ALWAYS_DEFINES_JDK $TOOLCHAIN_CFLAGS_JDK \
       $OS_CFLAGS $CFLAGS_OS_DEF_JDK $DEBUG_CFLAGS_JDK $DEBUG_OPTIONS_FLAGS_JDK \
-      $WARNING_CFLAGS $WARNING_CFLAGS_JDK $DEBUG_SYMBOLS_CFLAGS_JDK \
+      $DEBUG_SYMBOLS_CFLAGS_JDK \
       $FILE_MACRO_CFLAGS $REPRODUCIBLE_CFLAGS $BRANCH_PROTECTION_CFLAGS"
 
   # Use ${$2EXTRA_CFLAGS} to block EXTRA_CFLAGS to be added to build flags.