RFR: 8365047: Remove exception handler stub code in C2 [v4]

[Amit Kumar]

On Fri, 12 Sep 2025 16:36:56 GMT, Ruben <duke at openjdk.org> wrote:

>> The C2 exception handler stub code is only a trampoline to the generated exception handler blob. This change removes the extra step on the way to the generated blob.
>> 
>> According to some comments in the source code, the exception handler stub code used to be patched upon deoptimization, however presumably these comments are outdated as the patching upon deoptimization happens for post-call NOPs only.
>
> Ruben has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Offset the deoptimization handler entry point
>    
>    Change-Id: I596317ec6a364b341e4642636fa5cf08f87ed722
>  - Revert "Ensure stub code is not adjacent to a call"

on s390, I see couple of test failure with: 


#  Internal Error (/home/amit/jdk/src/hotspot/share/code/nmethod.cpp:669), pid=574704, tid=574714
#  guarantee(pd != nullptr) failed: scope must be present

# Problematic frame:
# V  [libjvm.so+0x11253f4]  nmethod::scope_desc_at(unsigned char*)+0x14c


BT:

Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V  [libjvm.so+0x11253f4]  nmethod::scope_desc_at(unsigned char*)+0x14c  (nmethod.cpp:669)
V  [libjvm.so+0x159b46c]  compiledVFrame::compiledVFrame(frame const*, RegisterMap const*, JavaThread*, nmethod*)+0x6c  (vframe_hp.cpp:305)
V  [libjvm.so+0x158f354]  vframe::new_vframe(frame const*, RegisterMap const*, JavaThread*) [clone .part.0]+0x5c  (vframe.cpp:75)
V  [libjvm.so+0x825f42]  Deoptimization::fetch_unroll_info_helper(JavaThread*, int)+0x222  (deoptimization.cpp:517)
V  [libjvm.so+0x827214]  Deoptimization::fetch_unroll_info(JavaThread*, int)+0x64  (deoptimization.cpp:299)
v  ~DeoptimizationBlob 0x000003ffa064fb92
J 265 c2 java.net.URL.<init>(Ljava/lang/String;Ljava/lang/String;ILjava/lang/String;Ljava/net/URLStreamHandler;)V java.base at 26-internal (417 bytes) @ 0x000003ffa066b08c [0x000003ffa066a680+0x0000000000000a0c]
J 256 c2 sun.net.www.ParseUtil.fileToEncodedURL(Ljava/io/File;)Ljava/net/URL; java.base at 26-internal (90 bytes) @ 0x000003ffa06688a0 [0x000003ffa0668740+0x0000000000000160]
j  jdk.internal.loader.URLClassPath.toFileURL(Ljava/lang/String;)Ljava/net/URL;+13 java.base at 26-internal
j  jdk.internal.loader.URLClassPath.<init>(Ljava/lang/String;Z)V+96 java.base at 26-internal
j  jdk.internal.loader.ClassLoaders.<clinit>()V+153 java.base at 26-internal
v  ~StubRoutines::Stub Generator call_stub_stub 0x000003ffa0500adc
C  0x000003ffb07ff840
V  [libjvm.so+0xbec91a]  JavaCalls::call(JavaValue*, methodHandle const&, JavaCallArguments*, JavaThread*)+0x42  (javaCalls.cpp:323)
V  [libjvm.so+0xb9a602]  InstanceKlass::call_class_initializer(JavaThread*)+0x2ba  (instanceKlass.cpp:1713)
V  [libjvm.so+0xb9dcec]  InstanceKlass::initialize_impl(JavaThread*)+0x60c  (instanceKlass.cpp:1321)
V  [libjvm.so+0xb9e2ea]  InstanceKlass::initialize(JavaThread*)+0xb2  (instanceKlass.cpp:819)
V  [libjvm.so+0xf337f6]  LinkResolver::resolve_static_call(CallInfo&, LinkInfo const&, bool, JavaThread*)+0xce  (linkResolver.cpp:1115)
V  [libjvm.so+0xf33ad0]  LinkResolver::resolve_invokestatic(CallInfo&, constantPoolHandle const&, int, JavaThread*)+0x88  (linkResolver.cpp:1744)
V  [libjvm.so+0xf377e4]  LinkResolver::resolve_invoke(CallInfo&, Handle, constantPoolHandle const&, int, Bytecodes::Code, JavaThread*)+0xdc  (linkResolver.cpp:1703)
V  [libjvm.so+0xbd1656]  InterpreterRuntime::resolve_invoke(JavaThread*, Bytecodes::Code)+0x1ce  (interpreterRuntime.cpp:826)
V  [libjvm.so+0xbd1dc6]  InterpreterRuntime::resolve_from_cache(JavaThread*, Bytecodes::Code)+0x96  (interpreterRuntime.cpp:1005)
j  jdk.internal.module.ModuleBootstrap.boot()Ljava/lang/ModuleLayer;+40 java.base at 26-internal
j  java.lang.System.initPhase2(ZZ)I+0 java.base at 26-internal
v  ~StubRoutines::Stub Generator call_stub_stub 0x000003ffa0500adc
C  0x000003ffb07fc7c8
V  [libjvm.so+0xbeecc4]  JavaCalls::call_static(JavaValue*, Klass*, Symbol*, Symbol*, JavaCallArguments*, JavaThread*)+0x1ac  (javaCalls.cpp:323)
V  [libjvm.so+0x14dd554]  Threads::create_vm(JavaVMInitArgs*, bool*)+0x8ac  (threads.cpp:322)
V  [libjvm.so+0xd3593e]  JNI_CreateJavaVM+0x7e  (jni.cpp:3589)
C  [libjli.so+0x4170]  JavaMain+0xa0  (java.c:1506)
C  [libjli.so+0x7f38]  ThreadJavaMain+0x20  (java_md.c:646)
Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)
v  ~DeoptimizationBlob 0x000003ffa064fb92
J 265 c2 java.net.URL.<init>(Ljava/lang/String;Ljava/lang/String;ILjava/lang/String;Ljava/net/URLStreamHandler;)V java.base at 26-internal (417 bytes) @ 0x000003ffa066b08c [0x000003ffa066a680+0x0000000000000a0c]

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PR Comment: https://git.openjdk.org/jdk/pull/26678#issuecomment-3301461222