From 909d4e758c045a0d8cea52f6a1333839f7d6c43e Mon Sep 17 00:00:00 2001
From: Matthias Baesken <mbaesken@openjdk.org>
Date: Mon, 13 Apr 2026 07:20:16 +0000
Subject: [PATCH] 8378838: Fix issues with "dead" code elimination and
 serviceability agent in libjvm.so on Linux

Reviewed-by: lucy, erikj
---
 make/autoconf/flags-cflags.m4  |  5 +----
 make/autoconf/flags-ldflags.m4 | 13 ++++++-------
 2 files changed, 7 insertions(+), 11 deletions(-)

diff --git a/make/autoconf/flags-cflags.m4 b/make/autoconf/flags-cflags.m4
index ab9cd8be19b..423654cd50a 100644
--- a/make/autoconf/flags-cflags.m4
+++ b/make/autoconf/flags-cflags.m4
@@ -544,12 +544,9 @@ AC_DEFUN([FLAGS_SETUP_CFLAGS_HELPER],
     TOOLCHAIN_CFLAGS_JVM="$TOOLCHAIN_CFLAGS_JVM -fstack-protector"
     TOOLCHAIN_CFLAGS_JDK="-fvisibility=hidden -pipe -fstack-protector"
     # reduce lib size on linux in link step, this needs also special compile flags
-    # do this on s390x also for libjvm (where serviceability agent is not supported)
     if test "x$ENABLE_LINKTIME_GC" = xtrue; then
       TOOLCHAIN_CFLAGS_JDK="$TOOLCHAIN_CFLAGS_JDK -ffunction-sections -fdata-sections"
-      if test "x$OPENJDK_TARGET_CPU" = xs390x && test "x$DEBUG_LEVEL" == xrelease; then
-        TOOLCHAIN_CFLAGS_JVM="$TOOLCHAIN_CFLAGS_JVM -ffunction-sections -fdata-sections"
-      fi
+      TOOLCHAIN_CFLAGS_JVM="$TOOLCHAIN_CFLAGS_JVM -ffunction-sections -fdata-sections"
     fi
     # technically NOT for CXX (but since this gives *worse* performance, use
     # no-strict-aliasing everywhere!)
diff --git a/make/autoconf/flags-ldflags.m4 b/make/autoconf/flags-ldflags.m4
index 7782735be25..ff10828731e 100644
--- a/make/autoconf/flags-ldflags.m4
+++ b/make/autoconf/flags-ldflags.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
@@ -53,16 +53,15 @@ AC_DEFUN([FLAGS_SETUP_LDFLAGS_HELPER],
     # add --icf=all (Identical Code Folding — merges identical functions)
     BASIC_LDFLAGS="-Wl,-z,defs -Wl,-z,relro -Wl,-z,now -Wl,--no-as-needed -Wl,--exclude-libs,ALL"
 
+    BASIC_LDFLAGS_JVM_ONLY=""
     # Linux : remove unused code+data in link step
     if test "x$ENABLE_LINKTIME_GC" = xtrue; then
-      if test "x$OPENJDK_TARGET_CPU" = xs390x; then
-        BASIC_LDFLAGS="$BASIC_LDFLAGS -Wl,--gc-sections"
-      else
-        BASIC_LDFLAGS_JDK_ONLY="$BASIC_LDFLAGS_JDK_ONLY -Wl,--gc-sections"
-      fi
+      # keep vtables : -Wl,--undefined-glob=_ZTV* (but this seems not to work with gold ld)
+      # so keep at least the Metadata vtable that is used in the serviceability agent
+      BASIC_LDFLAGS_JVM_ONLY="$BASIC_LDFLAGS_JVM_ONLY -Wl,--gc-sections -Wl,--undefined=_ZTV8Metadata"
+      BASIC_LDFLAGS_JDK_ONLY="$BASIC_LDFLAGS_JDK_ONLY -Wl,--gc-sections"
     fi
 
-    BASIC_LDFLAGS_JVM_ONLY=""
     LDFLAGS_LTO="-flto=auto -fuse-linker-plugin -fno-strict-aliasing $DEBUG_PREFIX_CFLAGS"
 
     LDFLAGS_CXX_PARTIAL_LINKING="$MACHINE_FLAG -r"