8358694: VM asserts if CodeCacheSegmentSize is not a power of 2

Reviewed-by: shade, dfenacci

Author: offamitkumar

src/hotspot/share/runtime/flags/jvmFlagConstraintsCompiler.cpp

@@ -156,6 +156,13 @@ JVMFlag::Error OnStackReplacePercentageConstraintFunc(intx value, bool verbose)
 }
 
 JVMFlag::Error CodeCacheSegmentSizeConstraintFunc(size_t value, bool verbose) {
+  if (!is_power_of_2(value)) {
+    JVMFlag::printError(verbose,
+                        "CodeCacheSegmentSize (%zu) must be "
+                        "a power of two\n", CodeCacheSegmentSize);
+    return JVMFlag::VIOLATES_CONSTRAINT;
+  }
+
   if (CodeCacheSegmentSize < (size_t)CodeEntryAlignment) {
     JVMFlag::printError(verbose,
                         "CodeCacheSegmentSize  (%zu) must be "

test/hotspot/jtreg/compiler/codecache/CodeCacheSegmentSizeTest.java

@@ -0,0 +1,77 @@
+/*
+ * Copyright (c) 2025 IBM Corporation. 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8358694
+ * @summary Verifies that CodeCacheSegmentSize enforces power-of-two constraint:
+ *          - fails gracefully for invalid value
+ *          - succeeds for valid value
+ * @library /test/lib
+ * @run driver CodeCacheSegmentSizeTest
+ */
+
+import jdk.test.lib.Platform;
+import jdk.test.lib.process.ProcessTools;
+import jdk.test.lib.process.OutputAnalyzer;
+
+public class CodeCacheSegmentSizeTest {
+    public static void main(String[] args) throws Exception {
+        testInvalidValue();
+        testValidValue();
+    }
+
+    private static void testInvalidValue() throws Exception {
+        ProcessBuilder pb = ProcessTools.createLimitedTestJavaProcessBuilder(
+            "-XX:+UnlockExperimentalVMOptions",
+            "-XX:CodeCacheSegmentSize=65", // invalid value (not power of two)
+            "-version"
+        );
+
+        OutputAnalyzer output = new OutputAnalyzer(pb.start());
+
+        // Ensure no crash (no assert failure)
+        output.shouldNotContain("assert");
+
+        // Expected graceful error output
+        output.shouldContain("CodeCacheSegmentSize (65) must be a power of two");
+        output.shouldContain("Error: Could not create the Java Virtual Machine.");
+        output.shouldContain("Error: A fatal exception has occurred. Program will exit.");
+
+        // Graceful exit with error code 1
+        output.shouldHaveExitValue(1);
+    }
+
+    private static void testValidValue() throws Exception {
+        ProcessBuilder pb = ProcessTools.createLimitedTestJavaProcessBuilder(
+            "-XX:+UnlockExperimentalVMOptions",
+            "-XX:CodeCacheSegmentSize=64", // a valid power of 2
+            "-version"
+        );
+
+        OutputAnalyzer output = new OutputAnalyzer(pb.start());
+
+        output.shouldHaveExitValue(0);
+    }
+}
+