Separate builder and guest libc selection state

Keep the existing LibCBase API unchanged for builder and host-analyzed callers. Introduce a shared LibCKind value, rematerialize it in the guest context, and expose guest-owned folded predicates where runtime code is already guest-owned.

Migrate PosixPlatformThreads to that guest state. Truffle NFI remains on its existing builder-folded LibCBase query until that code is migrated separately.

Author: d-kozak

substratevm/mx.substratevm/suite.py

@@ -588,6 +588,8 @@
                 "com.oracle.svm.hosted",
                 "com.oracle.svm.core.graal.aarch64",
                 "com.oracle.svm.core.graal.riscv64",
+                # GR-73521: Remove once PosixPlatformThreads moves to guest-owned code.
+                "SVM_GUEST_STAGING",
             ],
             "requiresConcealed" : {
                 "java.base" : [

substratevm/src/com.oracle.svm.core.posix/src/com/oracle/svm/core/posix/thread/PosixPlatformThreads.java

@@ -48,16 +48,13 @@
 import com.oracle.svm.core.annotate.Inject;
 import com.oracle.svm.core.annotate.RecomputeFieldValue;
 import com.oracle.svm.core.annotate.TargetClass;
-import com.oracle.svm.core.c.libc.BionicLibC;
-import com.oracle.svm.core.c.libc.GLibC;
-import com.oracle.svm.core.c.libc.LibCBase;
-import com.oracle.svm.core.c.libc.MuslLibC;
 import com.oracle.svm.core.graal.stackvalue.UnsafeStackValue;
 import com.oracle.svm.core.memory.NativeMemory;
 import com.oracle.svm.core.nmt.NmtCategory;
 import com.oracle.svm.core.posix.PosixUtils;
 import com.oracle.svm.core.posix.headers.Errno;
 import com.oracle.svm.core.posix.headers.Pthread;
+import com.oracle.svm.guest.staging.config.SubstrateGuestLibC;
 import com.oracle.svm.core.posix.headers.Pthread.pthread_attr_t;
 import com.oracle.svm.core.posix.headers.Pthread.pthread_cond_t;
 import com.oracle.svm.core.posix.headers.Pthread.pthread_mutex_t;
@@ -150,10 +147,10 @@ private static UnsignedWord computeNativeStackSize(pthread_attr_t attributes, lo
     @Uninterruptible(reason = CALLED_FROM_UNINTERRUPTIBLE_CODE, mayBeInlined = true)
     public static UnsignedWord computeGuardSizeIncludedInStackSize(pthread_attr_t attr) {
         if (Platform.includedIn(Platform.LINUX.class)) {
-            if (LibCBase.targetLibCIs(MuslLibC.class)) {
+            if (SubstrateGuestLibC.isMusl()) {
                 /* pthread_attr_getstack() already excludes the guard size correctly. */
                 return Word.zero();
-            } else if (LibCBase.targetLibCIs(GLibC.class) || LibCBase.targetLibCIs(BionicLibC.class)) {
+            } else if (SubstrateGuestLibC.isGLibC() || SubstrateGuestLibC.isBionic()) {
                 /* pthread_attr_getstack() includes the guard size, so determine and subtract the guard size. */
                 WordPointer guardSizePtr = StackValue.get(WordPointer.class);
                 if (Pthread.pthread_attr_getguardsize(attr, guardSizePtr) != 0) {

substratevm/src/com.oracle.svm.guest.staging/src/com/oracle/svm/guest/staging/config/SubstrateGuestLibC.java

@@ -0,0 +1,81 @@
+/*
+ * Copyright (c) 2026, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * 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.
+ */
+package com.oracle.svm.guest.staging.config;
+
+import org.graalvm.nativeimage.ImageSingletons;
+
+import com.oracle.svm.shared.c.libc.LibCKind;
+import com.oracle.svm.shared.meta.GuestFold;
+import com.oracle.svm.shared.singletons.traits.BuiltinTraits.BuildtimeAccessOnly;
+import com.oracle.svm.shared.singletons.traits.BuiltinTraits.NoLayeredCallbacks;
+import com.oracle.svm.shared.singletons.traits.SingletonTraits;
+
+/**
+ * Guest-owned target libc identity derived from the authoritative builder selection.
+ * <p>
+ * Although the query methods are called from runtime-owned code, every query is
+ * {@link GuestFold folded} while the image is built. The fold executes in the guest context and
+ * replaces the call with a boolean constant, so neither this singleton nor its
+ * {@link ImageSingletons#lookup(Class) lookup} is needed at image runtime. Consequently, this
+ * singleton deliberately permits build-time access only.
+ */
+@SingletonTraits(access = BuildtimeAccessOnly.class, layeredCallbacks = NoLayeredCallbacks.class)
+public final class SubstrateGuestLibC {
+
+    private final LibCKind kind;
+
+    /**
+     * Creates the guest-owned libc metadata from a shared enum name. Passing the name lets the enum
+     * value be materialized inside the guest context instead of transferring a builder object.
+     *
+     * @param kindName the {@link LibCKind} constant name
+     */
+    public SubstrateGuestLibC(String kindName) {
+        this.kind = LibCKind.valueOf(kindName);
+    }
+
+    /** Returns whether the target uses musl libc. */
+    @GuestFold
+    public static boolean isMusl() {
+        return singleton().kind == LibCKind.MUSL;
+    }
+
+    /** Returns whether the target uses glibc. */
+    @GuestFold
+    public static boolean isGLibC() {
+        return singleton().kind == LibCKind.GLIBC;
+    }
+
+    /** Returns whether the target uses Bionic libc. */
+    @GuestFold
+    public static boolean isBionic() {
+        return singleton().kind == LibCKind.BIONIC;
+    }
+
+    /** Returns the libc metadata installed in the guest singleton registry. */
+    private static SubstrateGuestLibC singleton() {
+        return ImageSingletons.lookup(SubstrateGuestLibC.class);
+    }
+}

substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/NativeImageGenerator.java

@@ -130,7 +130,10 @@
 import com.oracle.svm.core.ParsingReason;
 import com.oracle.svm.core.SubstrateOptions;
 import com.oracle.svm.core.SubstrateTarget;
+import com.oracle.svm.core.c.libc.BionicLibC;
+import com.oracle.svm.core.c.libc.GLibC;
 import com.oracle.svm.core.c.libc.LibCBase;
+import com.oracle.svm.core.c.libc.MuslLibC;
 import com.oracle.svm.core.c.libc.NoLibC;
 import com.oracle.svm.core.c.libc.TemporaryBuildDirectoryProvider;
 import com.oracle.svm.core.c.struct.OffsetOf;
@@ -174,6 +177,7 @@
 import com.oracle.svm.core.util.UserError;
 import com.oracle.svm.guest.staging.ArgsSupport;
 import com.oracle.svm.guest.staging.JavaMainSupport;
+import com.oracle.svm.guest.staging.config.SubstrateGuestLibC;
 import com.oracle.svm.guest.staging.config.SubstrateGuestTarget;
 import com.oracle.svm.guest.staging.jdk.RuntimeSupport;
 import com.oracle.svm.guest.staging.option.RuntimeOptionValidationSupport;
@@ -273,6 +277,7 @@
 import com.oracle.svm.hosted.util.CPUTypeAMD64;
 import com.oracle.svm.hosted.util.CPUTypeRISCV64;
 import com.oracle.svm.shared.ImageLayerBuildingSupportProvider;
+import com.oracle.svm.shared.c.libc.LibCKind;
 import com.oracle.svm.shared.option.HostedOptionValues;
 import com.oracle.svm.shared.option.OptionClassFilter;
 import com.oracle.svm.shared.option.SubstrateOptionsParser;
@@ -1104,6 +1109,7 @@ protected void setupNativeImage(OptionValues options, Map<ResolvedJavaMethod, CE
                 featureHandler.forEachFeature(feature -> feature.afterRegistration(access));
                 DynamicAccessSupport.setRegistrationSealed();
                 setDefaultLibCIfMissing();
+                setupGuestLibC();
                 MainEntryPoint accessMainEntryPoint = access.getMainEntryPoint();
                 if (accessMainEntryPoint != null) {
                     setAndVerifyMainEntryPoint(accessMainEntryPoint, entryPoints);
@@ -1374,6 +1380,26 @@ private static void setupGuestTargetDescription(SubstrateTarget target) {
         GuestImageSingletonSupport.add(SubstrateGuestTarget.class, guestTargetDescription);
     }
 
+    /**
+     * Installs the guest-owned target libc identity derived from the authoritative builder
+     * selection. Only the enum name crosses the context boundary; the enum value and singleton are
+     * created in the guest context. The singleton is used only while folding guest queries during
+     * image building; the folded boolean constants are what remain in runtime code.
+     */
+    private static void setupGuestLibC() {
+        GuestAccess access = GuestAccess.get();
+        LibCKind kind = switch (LibCBase.singleton()) {
+            case GLibC _ -> LibCKind.GLIBC;
+            case MuslLibC _ -> LibCKind.MUSL;
+            case BionicLibC _ -> LibCKind.BIONIC;
+            case NoLibC _ -> LibCKind.NOT_APPLICABLE;
+            case LibCBase libC -> throw VMError.shouldNotReachHere("Unknown target libc implementation: " + libC.getClass().getName());
+        };
+        ResolvedJavaMethod ctor = JVMCIReflectionUtil.getDeclaredConstructor(access.getProviders().getMetaAccess(), SubstrateGuestLibC.class, String.class);
+        JavaConstant guestLibC = access.invoke(ctor, null, access.asGuestString(kind.name()));
+        GuestImageSingletonSupport.add(SubstrateGuestLibC.class, guestLibC);
+    }
+
     /**
      * Filters out internal user features from the report.
      */

substratevm/src/com.oracle.svm.shared/src/com/oracle/svm/shared/c/libc/LibCKind.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2026, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * 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.
+ */
+package com.oracle.svm.shared.c.libc;
+
+/** Identifies the target C library without carrying any builder-specific behavior. */
+public enum LibCKind {
+    /** GNU C Library. */
+    GLIBC,
+    /** musl libc. */
+    MUSL,
+    /** Android Bionic libc. */
+    BIONIC,
+    /** No target C library applies. */
+    NOT_APPLICABLE
+}