RFR: 8352251: Implement Cooperative JFR Sampling [v12]

[Martin Doerr]

On Thu, 24 Apr 2025 09:53:38 GMT, Markus Grönlund <mgronlun at openjdk.org> wrote:

>> Greetings,
>> 
>> This is the implementation of JEP [JDK-8350338 Cooperative JFR Sampling](https://bugs.openjdk.org/browse/JDK-8350338).
>> 
>> Implementations in this change set are provided and have been tested on the following platforms:
>> 
>> - windows-x64
>> - windows-x64-debug
>> - linux-x64
>> - linux-x64-debug
>> - macosx-x64
>> - macosx-x64-debug
>> - linux-aarch64
>> - linux-aarch64-debug
>> - macosx-aarch64
>> - macosx-aarch64-debug
>> 
>> Testing: tier1-6, jdk_jfr, stress testing.
>> 
>> Platform porters note:
>> Some platform-specific code needs to be provided, mainly in the interpreter. Take a look at the following files for changes:
>> 
>> - src/hotspot/cpu/x86/frame_x86.cpp
>> - src/hotspot/cpu/x86/interp_masm_x86.cpp
>> - src/hotspot/cpu/x86/interp_masm_x86.hpp
>> - src/hotspot/cpu/x86/javaFrameAnchor_x86.hpp
>> - src/hotspot/cpu/x86/macroAssembler_x86.cpp
>> - src/hotspot/cpu/x86/macroAssembler_x86.hpp
>> - src/hotspot/cpu/x86/templateInterpreterGenerator_x86.cpp
>> - src/hotspot/cpu/x86/templateTable_x86.cpp
>> - src/hotspot/os_cpu/linux_x86/javaThread_linux_x86.hpp
>> 
>> Thanks
>> Markus
>
> Markus Grönlund has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Attempt to build Windows-AARCH64

Hi, I've taken a quick look and wonder what needs to be done for PPC64 which has some fundamental differences.

We never need to pass an FP because it can always be retrieved like this via Back Chain (required by "Power Architecture 64-Bit ELF V2 ABI Specification"): FP = *SP
So, I guess we could use something like

diff --git a/src/hotspot/cpu/ppc/javaFrameAnchor_ppc.hpp b/src/hotspot/cpu/ppc/javaFrameAnchor_ppc.hpp
index 8b539bc8101..7d07c302b36 100644
--- a/src/hotspot/cpu/ppc/javaFrameAnchor_ppc.hpp
+++ b/src/hotspot/cpu/ppc/javaFrameAnchor_ppc.hpp
@@ -73,6 +73,10 @@
 
   address last_Java_pc(void)          { return _last_Java_pc; }
 
+  intptr_t* last_Java_fp() const      { return *(intptr_t**)_last_Java_sp; }
+
+  intptr_t* last_sender_Java_fp() const { return **(intptr_t***)_last_Java_sp; }
+
   void set_last_Java_sp(intptr_t* sp) { OrderAccess::release(); _last_Java_sp = sp; }
 
 #endif // CPU_PPC_JAVAFRAMEANCHOR_PPC_HPP


This frame constructor does not exist on PPC64:
https://github.com/openjdk/jdk/blob/771a397a12a3bcb25af1f508061fd928d8f13c2e/src/hotspot/share/jfr/periodic/sampling/jfrThreadSampling.cpp#L174
We have one with different argument order and could emulate it like this:
```C++
inline frame::frame(intptr_t* sp, intptr_t* unextended_sp, intptr_t* sender_sp, address pc, CodeBlob* cb) :
  frame(sp, pc, unextended_sp, sender_sp, cb) {}

Strange if we really need another one which only turns the argument order.

The following constants do not exist:
```C++
    // Used by JFR. Unfortunately, we can't use offset_of because it's not constexpr.
    ijava_state_slots                      = ijava_state_size >> LogBytesPerWord,
    // Members of ijava_state:
    interpreter_frame_method_offset        = -ijava_state_slots + 0,
    interpreter_frame_bcp_offset           = -ijava_state_slots + 5,
    interpreter_frame_sender_sp_offset     = -ijava_state_slots + 9,
    // Stuff which shouldn't be used on this platform:
    interpreter_frame_initial_sp_offset    = -ijava_state_slots,
    link_offset                            = 0,
    sender_sp_offset                       = 0,
    // Member of common_abi: lr
    return_addr_offset                     = 2,

I hate adding them. Could we move the usages into platform code?

-------------

PR Comment: https://git.openjdk.org/jdk/pull/24296#issuecomment-2830943762