RFR (XL): 8152664 - Support non-continuous CodeBlobs in HotSpot
Rickard Bäckman
rickard.backman at oracle.com
Mon Apr 11 09:05:01 UTC 2016
Volker,
thanks for finding this issue.
I think that maybe the easiest fix is as follows:
create new virtual methods in CompiledMethod:
virtual address stub_begin_v() = 0;
make the now virtual stub_begin non-virtual like:
address stub_begin() { return stub_begin_v(); }
in nmethod we override the stub_begin() with the normal this + offset
compuation and implement stub_begin_v() to call stub_begin().
That will avoid all virtual calls in the case were we are not working on
a CompiledMethod.
It adds a couple of methods though. What do you think?
/R
On 04/08, 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
> >
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