RFR (XL): 8152664 - Support non-continuous CodeBlobs in HotSpot

Dean Long dean.long at oracle.com
Fri Apr 8 20:04:45 UTC 2016


Hi Volker.  I noticed this problem before and filed 8151956.  Making 
those member functions
non-virtual may solve this particular problem, but as the code evolves 
we may hit it
again if we ever call a virtual member function by accident.

I'm not a C++ expert, but if we declared those functions as virtual in 
CodeBlob, then would
that work?  It doesn't seem ideal, however.  I would rather not call out 
from the CodeBlob
constructor at all, but instead do the work in the subclass 
constructor.  Let's say we move
the call to  cb->copy_code_and_locs_to() to a separate function. Is 
there a C++ idiom
for making sure all subclasses of CodeBlob call it?  The only think I 
can think of is to set
an "initialized" flag and to check it in strategic places.

dl

On 4/8/2016 11:12 AM, Volker Simonis wrote:
> Hi Rickard,
>
> I found the problem why your change crashes the VM on ppc (and I'm pretty
> sure it will also crash on ARM - @Andrew, maybe you can try it out?). It is
> caused by the following code in address NativeCall::get_trampoline() which
> is also present on arm64:
>
> address NativeCall::get_trampoline() {
>    address call_addr = addr_at(0);
>    CodeBlob *code = CodeCache::find_blob(call_addr);
> ...
>    // If the codeBlob is not a nmethod, this is because we get here from the
>    // CodeBlob constructor, which is called within the nmethod constructor.
>    return trampoline_stub_Relocation::get_trampoline_for(call_addr,
> (nmethod*)code);
> }
>
> The comment explains the situation quite well: we're in the CodeBlob
> constructor which was called by the CompiledMethod constructor which was
> called from the nmethod constructor:
>
> #3  0x00003fffb741b80c in NativeCall::get_trampoline (this=0x3fff607d0fac)
> at
> /usr/work/d046063/OpenJDK/jdk9-hs-comp/hotspot/src/cpu/ppc/vm/nativeInst_ppc.cpp:146
> #4  0x00003fffb7596914 in Relocation::pd_call_destination
> (this=0x3ffdfe3fcc90, orig_addr=0x3fff603b8a2c "\001") at
> /usr/work/d046063/OpenJDK/jdk9-hs-comp/hotspot/src/cpu/ppc/vm/relocInfo_ppc.cpp:87
> #5  0x00003fffb758f5fc in CallRelocation::fix_relocation_after_move
> (this=0x3ffdfe3fcc90, src=0x3ffdfe3fdb40, dest=0x3ffdfe3fcd58) at
> /usr/work/d046063/OpenJDK/jdk9-hs-comp/hotspot/src/share/vm/code/relocInfo.cpp:506
> #6  0x00003fffb6c48898 in CodeBuffer::relocate_code_to
> (this=0x3ffdfe3fdb40, dest=0x3ffdfe3fcd58) at
> /usr/work/d046063/OpenJDK/jdk9-hs-comp/hotspot/src/share/vm/asm/codeBuffer.cpp:812
> #7  0x00003fffb6c48404 in CodeBuffer::copy_code_to (this=0x3ffdfe3fdb40,
> dest_blob=0x3fff607d0c10) at
> /usr/work/d046063/OpenJDK/jdk9-hs-comp/hotspot/src/share/vm/asm/codeBuffer.cpp:748
> #8  0x00003fffb6c42670 in CodeBuffer::copy_code_and_locs_to
> (this=0x3ffdfe3fdb40, blob=0x3fff607d0c10) at
> /usr/work/d046063/OpenJDK/jdk9-hs-comp/hotspot/src/share/vm/asm/codeBuffer.hpp:607
> #9  0x00003fffb6c3f834 in CodeBlob::CodeBlob (this=0x3fff607d0c10,
> name=0x3fffb7a75fd8 "nmethod", layout=..., cb=0x3ffdfe3fdb40,
> frame_complete_offset=20, frame_size=14, oop_maps=0x3ffe00049620,
> caller_must_gc_arguments=false, subtype=8) at
> /usr/work/d046063/OpenJDK/jdk9-hs-comp/hotspot/src/share/vm/code/codeBlob.cpp:117
> #10 0x00003fffb6ce52c8 in CompiledMethod::CompiledMethod
> (this=0x3fff607d0c10, method=0x3ffe1ddce568, name=0x3fffb7a75fd8 "nmethod",
> size=1768, header_size=392, cb=0x3ffdfe3fdb40, frame_complete_offset=20,
> frame_size=14, oop_maps=0x3ffe00049620, caller_must_gc_arguments=false) at
> /usr/work/d046063/OpenJDK/jdk9-hs-comp/hotspot/src/share/vm/code/compiledMethod.cpp:42
> #11 0x00003fffb7421f58 in nmethod::nmethod (this=0x3fff607d0c10,
> method=0x3ffe1ddce568, nmethod_size=1768, compile_id=4, entry_bci=-1,
> offsets=0x3ffdfe3fdb18, orig_pc_offset=104, debug_info=0x3fffb03d55f0,
> dependencies=0x3ffe00049690, code_buffer=0x3ffdfe3fdb40, frame_size=14,
> oop_maps=0x3ffe00049620, handler_table=0x3ffdfe3fdad0,
> nul_chk_table=0x3ffdfe3fdaf0, compiler=0x3fffb03bc270, comp_level=3) at
> /usr/work/d046063/OpenJDK/jdk9-hs-comp/hotspot/src/share/vm/code/nmethod.cpp:706
>
> Now we cast 'code' to 'nmethod' but at this point in time 'code' is still a
> CodeBlob from the C++ point of view (i.e. it still has a CodeBlob vtable
> (see [1] for an explanation)).
>
> Later on, in RelocIterator::initialize() we call virtual methods on the
> nmethod which still has the vtable of a "CodeBlob" and this fails badly:
>
> #0  SingletonBlob::print_on (this=0x3fff607d0c10, st=0x0) at
> /usr/work/d046063/OpenJDK/jdk9-hs-comp/hotspot/src/share/vm/code/codeBlob.cpp:584
> #1  0x00003fffb758d51c in RelocIterator::initialize (this=0x3ffdfe3fc928,
> nm=0x3fff607d0c10, begin=0x3fff607d0fac "\001", limit=0x0) at
> /usr/work/d046063/OpenJDK/jdk9-hs-comp/hotspot/src/share/vm/code/relocInfo.cpp:144
> #2  0x00003fffb6ace56c in RelocIterator::RelocIterator
> (this=0x3ffdfe3fc928, nm=0x3fff607d0c10, begin=0x3fff607d0fac "\001",
> limit=0x0) at
> /usr/work/d046063/OpenJDK/jdk9-hs-comp/hotspot/src/share/vm/code/relocInfo.hpp:1378
> #3  0x00003fffb75919dc in trampoline_stub_Relocation::get_trampoline_for
> (call=0x3fff607d0fac "\001", code=0x3fff607d0c10) at
> /usr/work/d046063/OpenJDK/jdk9-hs-comp/hotspot/src/share/vm/code/relocInfo.cpp:849
> #4  0x00003fffb741b80c in NativeCall::get_trampoline (this=0x3fff607d0fac)
> at
> /usr/work/d046063/OpenJDK/jdk9-hs-comp/hotspot/src/cpu/ppc/vm/nativeInst_ppc.cpp:146
>
> As you can see, we actually want to call nmethod::stub_begin() at
> relocInfo.cpp:144
>
> 142  _section_start[CodeBuffer::SECT_CONSTS] = nm->consts_begin();
> 143  _section_start[CodeBuffer::SECT_INSTS ] = nm->insts_begin() ;
> 144  _section_start[CodeBuffer::SECT_STUBS ] = nm->stub_begin()  ;
>
> but we actually end up in SingletonBlob::print_on() which is a completely
> different method. Notice that the call to nm->consts_begin() before also
> fails, but it doesn't crash the VM because it happens to call
> SingletonBlob::verify() which has no bad side effect. The call to
> nm->insts_begin() in line 143 is non-virtual and thus works fine. Here are
> the corresponding vtable slots in the CodeBlob vtable for consts_begin()
> and stub_begin()
>
> (gdb) p &nmethod::consts_begin
> $76 = &virtual table offset 42
> (gdb) p &nmethod::stub_begin
> $77 = &virtual table offset 44
> (gdb) p  ((*(void ***)nm) + 1)[42]
> $86 = (void *) 0x3fffb6c41df8 <SingletonBlob::verify()>
> (gdb) p  ((*(void ***)nm) + 1)[44]
> $87 = (void *) 0x3fffb6c41e64 <SingletonBlob::print_on(outputStream*) const>
>
> As you can see, 'nm' is indeed a "CodeBlob" at this point:
>
> (gdb) p *(void ***)nm
> $91 = (void **) 0x3fffb7befa00 <vtable for CodeBlob+16>
> (gdb) p nm->print()
> [CodeBlob (0x00003fff607d1090)]
> Framesize: 14
>
> The offending calls succeeded before your change, because they where not
> virtual. Any idea how we can fix this with the new class hierarchy?
>
> Regards,
> Volker
>
> [1]
> http://stackoverflow.com/questions/6591859/when-does-the-vptr-pointing-to-vtable-get-initialized-for-a-polymorphic-class
>
>
>
> On Thu, Apr 7, 2016 at 5:50 PM, Volker Simonis <volker.simonis at gmail.com>
> wrote:
>
>> Hi Rickard,
>>
>> I'd also like to know what's the rational behind this quite large
>> change. Do you expect some performance or memory consumption
>> improvements or is this a prerequisite for another change which is
>> still to come?
>>
>> The change itself currently doesn't work on ppc64 (neither on Linux
>> nor on AIX). I get the following crash during the build when the newly
>> built Hotspot is JIT-compiling java.lang.String::charAt on C1 :
>>
>> #
>> # A fatal error has been detected by the Java Runtime Environment:
>> #
>> #  SIGSEGV (0xb) at pc=0x00001000012a44d0, pid=35331, tid=35404
>> #
>> # JRE version: OpenJDK Runtime Environment (9.0) (slowdebug build
>> 9-internal+0-2016-04-07-162501.d046063.jdk9-hs-comp)
>> # Java VM: OpenJDK 64-Bit Server VM (slowdebug
>> 9-internal+0-2016-04-07-162501.d046063.jdk9-hs-comp, mixed mode,
>> tiered, compressed oo
>> ps, serial gc, linux-ppc64le)
>> # Problematic frame:
>> # V  [libjvm.so+0xf744d0]  outputStream::do_vsnprintf_and_write(char
>> const*, char*, bool)+0x40
>> #
>> # No core dump will be written. Core dumps have been disabled. To
>> enable core dumping, try "ulimit -c unlimited" before starting Java
>>   again
>> #
>> # If you would like to submit a bug report, please visit:
>> #   http://bugreport.java.com/bugreport/crash.jsp
>> #
>>
>> ---------------  S U M M A R Y ------------
>>
>> Command Line:
>> -Dapplication.home=/sapmnt/ld9510/a/d046063/output-jdk9-hs-comp-dbg/jdk
>> -Xms8m -XX:+UseSerialGC -Xms32M -Xmx512M -Djdk.
>> module.main=jdk.jlink jdk.jlink/jdk.tools.jmod.Main create
>> --module-version 9-internal --os-name Linux --os-arch ppc64le
>> --os-version
>>   2.6 --modulepath /priv/d046063/output-jdk9-hs-comp-dbg/images/jmods
>> --hash-dependencies .* --exclude **_the.* --libs
>>
>> /priv/d046063/output-jdk9-hs-comp-dbg/support/modules_libs-stripped/java.base
>> --cmds
>> /priv/d046063/output-jdk9-hs-comp-dbg/support/modules_cmds-stripped/java.base
>> --config
>> /priv/d046063/output-jdk9-hs-comp-dbg/support/modules_conf/java.base
>> --class-path /priv/d046063/output-jdk9-hs-comp-dbg/jdk/modules/java.base
>> /priv/d046063/output-jdk9-hs-comp-dbg/support/jmods/java.base.jmod
>>
>> Host: ld9510, POWER8E (raw), altivec supported, 48 cores, 61G, #
>> Please check /etc/os-release for details about this release.
>> Time: Thu Apr  7 16:28:55 2016 CEST elapsed time: 0 seconds (0d 0h 0m 0s)
>>
>> ---------------  T H R E A D  ---------------
>>
>> Current thread (0x000010000429c800):  JavaThread "C1 CompilerThread10"
>> daemon [_thread_in_vm, id=35404,
>> stack(0x000010006a800000,0x000010006ac00000)]
>>
>>
>> Current CompileTask:
>> C1:    761    3       3       java.lang.String::charAt (25 bytes)
>>
>> Stack: [0x000010006a800000,0x000010006ac00000],
>> sp=0x000010006abfc6c0,  free space=4081k
>> Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native
>> code)
>> V  [libjvm.so+0xf744d0]  outputStream::do_vsnprintf_and_write(char
>> const*, char*, bool)+0x40
>> V  [libjvm.so+0xf74668]  outputStream::print_cr(char const*, ...)+0x68
>> V  [libjvm.so+0x72189c]  CodeBlob::print_on(outputStream*) const+0x50
>> V  [libjvm.so+0x723bdc]  RuntimeBlob::print_on(outputStream*) const+0x40
>> V  [libjvm.so+0x721eb0]  SingletonBlob::print_on(outputStream*) const+0x4c
>> V  [libjvm.so+0x106d51c]  RelocIterator::initialize(CompiledMethod*,
>> unsigned char*, unsigned char*)+0x170
>> V  [libjvm.so+0x5ae56c]  RelocIterator::RelocIterator(CompiledMethod*,
>> unsigned char*, unsigned char*)+0x78
>> V  [libjvm.so+0x10719dc]
>> trampoline_stub_Relocation::get_trampoline_for(unsigned char*,
>> nmethod*)+0x78
>> V  [libjvm.so+0xefb80c]  NativeCall::get_trampoline()+0x110
>> V  [libjvm.so+0x1076914]  Relocation::pd_call_destination(unsigned
>> char*)+0x150
>> V  [libjvm.so+0x106f5fc]
>> CallRelocation::fix_relocation_after_move(CodeBuffer const*,
>> CodeBuffer*)+0x74
>> V  [libjvm.so+0x728898]  CodeBuffer::relocate_code_to(CodeBuffer*)
>> const+0x390
>> V  [libjvm.so+0x728404]  CodeBuffer::copy_code_to(CodeBlob*)+0x134
>> V  [libjvm.so+0x722670]  CodeBuffer::copy_code_and_locs_to(CodeBlob*)+0x84
>> V  [libjvm.so+0x71f834]  CodeBlob::CodeBlob(char const*,
>> CodeBlobLayout const&, CodeBuffer*, int, int, OopMapSet*, bool,
>> int)+0x320
>> V  [libjvm.so+0x7c52c8]  CompiledMethod::CompiledMethod(Method*, char
>> const*, int, int, CodeBuffer*, int, int, OopMapSet*, bool)+0xd8
>> V  [libjvm.so+0xf01f58]  nmethod::nmethod(Method*, int, int, int,
>> CodeOffsets*, int, DebugInformationRecorder*, Dependencies*,
>> CodeBuffer*, int, OopMapSet*, ExceptionHandlerTable*,
>> ImplicitExceptionTable*, AbstractCompiler*, int)+0xe0
>> V  [libjvm.so+0xf01610]  nmethod::new_nmethod(methodHandle const&,
>> int, int, CodeOffsets*, int, DebugInformationRecorder*, Dependencies*,
>> CodeBuffer*, int, OopMapSet*, ExceptionHandlerTable*,
>> ImplicitExceptionTable*, AbstractCompiler*, int)+0x2c4
>> V  [libjvm.so+0x632970]  ciEnv::register_method(ciMethod*, int,
>> CodeOffsets*, int, CodeBuffer*, int, OopMapSet*,
>> ExceptionHandlerTable*, ImplicitExceptionTable*, AbstractCompiler*,
>> bool, bool, RTMState)+0x560
>> V  [libjvm.so+0x48ee00]  Compilation::install_code(int)+0x264
>> V  [libjvm.so+0x48eff8]  Compilation::compile_method()+0x184
>> V  [libjvm.so+0x48f7a8]  Compilation::Compilation(AbstractCompiler*,
>> ciEnv*, ciMethod*, int, BufferBlob*, DirectiveSet*)+0x288
>> V  [libjvm.so+0x4980d0]  Compiler::compile_method(ciEnv*, ciMethod*,
>> int, DirectiveSet*)+0xc8
>> V  [libjvm.so+0x7b188c]
>> CompileBroker::invoke_compiler_on_method(CompileTask*)+0x590
>> V  [libjvm.so+0x7b07bc]  CompileBroker::compiler_thread_loop()+0x310
>> V  [libjvm.so+0x11a614c]  compiler_thread_entry(JavaThread*, Thread*)+0xa0
>> V  [libjvm.so+0x119f3a8]  JavaThread::thread_main_inner()+0x1b4
>> V  [libjvm.so+0x119f1a4]  JavaThread::run()+0x1b8
>> V  [libjvm.so+0xf53d90]  java_start(Thread*)+0x204
>> C  [libpthread.so.0+0x8a64]  start_thread+0xf4
>> C  [libc.so.6+0x1032a0]  clone+0x98
>>
>> I haven't identified the exact cause (will analyze it tomorrow) but
>> the stack trace indicates that it is indeed related to your changes.
>>
>> Besides that I have some comments:
>>
>> codeBuffer.hpp:
>>
>> 472   CodeSection* insts() { return &_insts; }
>> 475   const CodeSection* insts() const { return &_insts; }
>>
>> - do we really need both versions?
>>
>> codeBlob.hpp:
>>
>>   135   nmethod* as_nmethod_or_null() const                { return
>> is_nmethod() ? (nmethod*) this : NULL; }
>>   136   nmethod* as_nmethod() const                        {
>> assert(is_nmethod(), "must be nmethod"); return (nmethod*) this; }
>>   137   CompiledMethod* as_compiled_method_or_null() const { return
>> is_compiled() ? (CompiledMethod*) this : NULL; }
>>   138   CompiledMethod* as_compiled_method() const         {
>> assert(is_compiled(), "must be compiled"); return (CompiledMethod*)
>> this; }
>>   139   CodeBlob* as_codeblob_or_null() const              { return
>> (CodeBlob*) this; }
>>
>> - I don't like this code. You make the getters 'const' which
>> implicitely makes 'this' a "pointer to const" but then the returned
>> pointer is a normal pointer to a non-const object and therefore you
>> have to statically cast away the "pointer to const" (that's why you
>> need the cast even in the case where you return a CodeBlob*). So
>> either remove the const qualifier from the method declarations or make
>> them return "pointers to const". And by the way, as_codeblob_or_null()
>> doesn't seemed to be used anywhere in the code, why do we need it at
>> all?
>>
>> - Why do we need the non-virtual methods is_nmethod() and
>> is_compiled() to manually simulate virtual behavior. Why can't we
>> simply make them virtual and implement them accordingly in nmathod and
>> CompiledMethod?
>>
>> Regards,
>> Volker
>>
>> On Thu, Apr 7, 2016 at 2:12 PM, Rickard Bäckman
>> <rickard.backman at oracle.com> wrote:
>>> Hi,
>>>
>>> can I please have review for this patch please?
>>>
>>> So far CodeBlobs have required all the data (metadata, oops, code, etc)
>>> to be in one continuous blob With this patch we are looking to change
>>> that. It's been done by changing offsets in CodeBlob to addresses,
>>> making some methods virtual to allow different behavior and also
>>> creating a couple of new classes. CompiledMethod now sits inbetween
>>> CodeBlob and nmethod.
>>>
>>> CR: https://bugs.openjdk.java.net/browse/JDK-8152664
>>> Webrev: http://cr.openjdk.java.net/~rbackman/8152664/
>>>
>>> Thanks
>>> /R



More information about the hotspot-dev mailing list