RFR(M): 8145221: Use trampolines for i2i and i2c entries in Methods that are stored in CDS archive

[Calvin Cheung]

Dean, Ioi,

Thanks for the review and discussions.

Here's an updated webrev:
http://cr.openjdk.java.net/~ccheung/8145221/webrev.01/

Changes in this webrev:
- in thread_*.cpp, added check in JavaThread::pd_get_top_frame(). Return 
if it is in the middle of a trampoline call.
- moved the guarantee from metaspaceShared_sparc.cpp to the common 
metaspaceShared.cpp;
- changed the MIN_SHARED_MISC_DATA_SIZE and MIN_SHARED_MISC_CODE_SIZE 
and related comment in metaspaceShared.hpp

The last 2 changes are required due to the test failure with the 
hotspot/test/runtime/CommandLine/OptionsValidation/TestOptionsWithRanges.java 
test.

Testing:
     JPRT with testset hotspot
     jtreg tests under hotspot/runtime on all platforms

thanks,
Calvin

p.s. I corrected the bug id in the subject line from 8145521 to 8145221


On 2/25/16, 10:03 AM, Ioi Lam wrote:
>
>
> On 2/22/16 12:50 PM, Dean Long wrote:
>> Hi Ioi, comments inlined below.
>>
>> On 2/20/2016 5:22 PM, Ioi Lam wrote:
>>> Hi Dean,
>>>
>>> Thanks for raising this issue.
>>>
>>> My first impression is this probably shouldn't matter (or somehow we 
>>> can get away with this).
>>>
>>> Today, the CDS archive already contains executable code in the "misc 
>>> code" section. On Linux/x64, this is typically in the address range 
>>> 0x802400000-0x802409000. The code is used to dynamically patch the 
>>> C++ vtables of Metadata types that are stored in the CDS archive. So 
>>> even today, there's a chance that the suspended PC lands in this 
>>> section.
>>>
>>
>> OK, so you're saying that the trampolines don't make things any worse 
>> :-)
>
> Well, theoretically the i2i and c2i entries would be executed more 
> frequently than the vtable patching code, so if there was a problem, 
> it could be aggravated.
>>
>>> The code is generated inside 
>>> MetaspaceShared::generate_vtable_methods and looks like this when 
>>> you run with -Xshare:on:
>>>
>>> (gdb) x/5i 0x802400000
>>>    0x802400000:    mov    $0x0,%eax
>>>    0x802400005:    jmpq   0x8024084d0
>>>    0x80240000a:    mov    $0x1,%eax
>>>    0x80240000f:    jmpq   0x8024084d0
>>>    0x802400014:    mov    $0x2,%eax
>>>    ....
>>> (gdb) x/16i 0x8024084d0
>>>    0x8024084d0:    push   %rsi
>>>    0x8024084d1:    push   %rdi
>>>    0x8024084d2:    mov    %rax,%rdi
>>>    0x8024084d5:    shr    $0x8,%rdi
>>>    0x8024084d9:    shl    $0x3,%rdi
>>>    0x8024084dd:    movabs $0x802000000,%rsi
>>>    0x8024084e7:    add    %rdi,%rsi
>>>    0x8024084ea:    mov    (%rsi),%rsi
>>>    0x8024084ed:    pop    %rdi
>>>    0x8024084ee:    mov    %rsi,(%rdi)
>>>    0x8024084f1:    and    $0xff,%rax
>>>    0x8024084f8:    shl    $0x3,%rax
>>>    0x8024084fc:    add    %rsi,%rax
>>>    0x8024084ff:    pop    %rsi
>>>    0x802408500:    mov    (%rax),%rax
>>>    0x802408503:    jmpq   *%rax
>>>
>>> In JDK9, the profiler takes a sample by first calling into 
>>> JavaThread::pd_get_top_frame_for_profiling:
>>>
>>> (gdb) where
>>> #0  frame::safe_for_sender (this=0x7ffec63895f0, thread=0x7ffff08ce000)
>>> #1  0x00007ffff69d72a7 in JavaThread::pd_get_top_frame 
>>> (this=0x7ffff08ce000, fr_addr=0x7ffec63897b0, 
>>> ucontext=0x7ffec6287d00, isInJava=true)
>>> #2  0x00007ffff69d70be in JavaThread::pd_get_top_frame_for_profiling 
>>> (this=0x7ffff08ce000, fr_addr=0x7ffec63897b0, ucontext=0x7ffec6287d00,
>>>     isInJava=true)
>>>
>>> I tried manually setting frame::_pc to 0x802400000, and it would 
>>> cause frame::safe_for_sender() to return false, and thus would 
>>> prevent the profiler from doing any stack walking.
>>>
>>
>> Was the reason safe_for_sender() failed something that we can rely on 
>> 100%?  I looked at safe_for_sender, and it's not obvious why it would 
>> fail, unless the frame pointer was invalid, and I think that depends 
>> on the platform and flags like PreserveFramePointer.  How about 
>> filing a separate bug to track this issue?
>>
>
> OK, I fill a new bug https://bugs.openjdk.java.net/browse/JDK-8150663 
> to track this.
>
> Thanks
> - Ioi
>
>> dl
>>
>>> Also, both the CDS vtable patching code and the i2i trampolines are 
>>> tail calls, so you will never find a PC in them except for the 
>>> top-most frame. This means the check in JavaThread::pd_get_top_frame 
>>> is enough. There's no need to do additional checks after we have 
>>> started stack walking.
>>>
>>> I think the chance of landing in the CDS vtable patching methods, or 
>>> in the trampolines, is pretty small, so that shouldn't bother the 
>>> sampling profiler too much.
>>>
>>> Anyway, as part of this bug, we should add a regression test with 
>>> the profiler enabled, and keep calling a method in the CDS archive 
>>> in a tight loop (and manually disable compilation of that method 
>>> using command-line options). The test should never crash, and if 
>>> possible, it should also check that we don't have too many "unknown" 
>>> samples.
>>>
>>> Thanks
>>> - Ioi
>>>
>>>
>>> On 2/19/16 4:39 PM, Dean Long wrote:
>>>> We have profiling code that will suspend a thread at random points 
>>>> and try to walk the stack.
>>>> I think frame::sender() will get confused if you happen to catch a 
>>>> thread in the trampoline,
>>>> and frame::_pc is in metadata and not the code cache.
>>>>
>>>> dl
>>>>
>>>> On 2/19/2016 2:19 PM, Calvin Cheung wrote:
>>>>> JBS: https://bugs.openjdk.java.net/browse/JDK-8145221
>>>>> webrev: http://cr.openjdk.java.net/~ccheung/8145221/webrev.00/
>>>>>
>>>>> This optimization reduces the size of the RW region of the CDS 
>>>>> archive. It also reduces the amount of pages in the RW region that 
>>>>> are actually written into during runtime.
>>>>>
>>>>> The original prototype on the x86_64 platform was done by Ioi 
>>>>> (ioi.lam at oracle.com).
>>>>> I helped porting it to other platforms.
>>>>> Special thanks to Goetz (goetz.lindenmaier at sap.com) who provided 
>>>>> the changes to the ppc platform.
>>>>>
>>>>> Testing:
>>>>>     JPRT with testset hotspot
>>>>>     maunal testing on X86_64, x86_32 and solaris/sparcv9 with 
>>>>> -XX:+PrintAssembly -XX:+PrintInterpreter
>>>>>     built on the Zero platform
>>>>>     tested on the openjdk aarch64 platform
>>>>>     refworkload on various platform (please refer to bug report 
>>>>> for data)
>>>>>
>>>>> thanks,
>>>>> Calvin
>>>>
>>>
>>
>