8324734: Relax too-strict assert(VM_Version::supports_evex()) in Assembler::locate_operand() #17590

rkennke · 2024-01-26T15:18:39Z

Details see bug report. The gist is that HotSpot downgrades to UseAVX=2 on some processors, and reports supports_evex() == false, but the instruction decoder can still encounter EVEX instructions when (e.g.) hitting a SIGBUS in memset() - which does have EVEX instructions.

Testing:

runtime/Unsafe/InternalErrorTest.java
tier1

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Issue

JDK-8324734: Relax too-strict assert(VM_Version::supports_evex()) in Assembler::locate_operand() (Bug - P3)

Reviewers

Vladimir Kozlov (@vnkozlov - Reviewer)
Aleksey Shipilev (@shipilev - Reviewer)

Contributors

Vladimir Kozlov <kvn@openjdk.org>

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$ git pull https://git.openjdk.org/jdk.git pull/17590/head

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…embler::locate_operand()

bridgekeeper · 2024-01-26T15:19:43Z

👋 Welcome back rkennke! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2024-01-26T15:21:01Z

@rkennke The following label will be automatically applied to this pull request:

hotspot-compiler

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mlbridge · 2024-01-26T15:23:46Z

Webrevs

vnkozlov

The assert is there to make sure HotSpot generates correct code.
What output you get in your test case with this change? You still crash in memset.

rkennke · 2024-01-26T19:42:08Z

The assert is there to make sure HotSpot generates correct code.

I understand, but the decoder here tries to decode non-HotSpot code, which can legitimately use EVEX instructions.

What output you get in your test case with this change? You still crash in memset.

The test-case passes with the change. The test provokes a SIGBUS and checks that it is propely turned into an InternalError. Without the change, it would crash with the assert, with the change the SIGBUS would be handled and turned into the expected InternalError.

What we could do is what Jorn suggests in JBS:
"As a long term solution, maybe VM_Version could distinguish between CPU features that are supported by the CPU, and features that are enabled. Then, the decoder could check whether evex is supported, while other code could be changed to check whether use of evex is enabled for hotspot's own code gen."
However, that seems more complex than what I'm currently willing to spend time on. ;-)

vnkozlov · 2024-01-26T21:00:02Z

VM_Version could distinguish between CPU features that are supported by the CPU
We can start with just EVEX check. It is not big change:

$ git diff
diff --git a/src/hotspot/cpu/x86/vm_version_x86.cpp b/src/hotspot/cpu/x86/vm_version_x86.cpp
index df1ea6edd30..8b4ca442b5a 100644
--- a/src/hotspot/cpu/x86/vm_version_x86.cpp
+++ b/src/hotspot/cpu/x86/vm_version_x86.cpp
@@ -809,7 +809,8 @@ void VM_Version::get_processor_features() {
   _stepping = cpu_stepping();
 
   if (cpu_family() > 4) { // it supports CPUID
-    _features = feature_flags();
+    _features = feature_flags(); // It can be changed by VM flags
+    _cpu_features = _features;   // Preserve features
     // Logical processors are only available on P4s and above,
     // and only if hyperthreading is available.
     _logical_processors_per_package = logical_processor_count();
diff --git a/src/hotspot/cpu/x86/vm_version_x86.hpp b/src/hotspot/cpu/x86/vm_version_x86.hpp
index e521a6ee3bc..de86ce51541 100644
--- a/src/hotspot/cpu/x86/vm_version_x86.hpp
+++ b/src/hotspot/cpu/x86/vm_version_x86.hpp
@@ -640,7 +640,7 @@ class VM_Version : public Abstract_VM_Version {
   }
 
   //
-  // Feature identification
+  // Feature identification which can be affected by VM flags
   //
   static bool supports_cpuid()        { return _features  != 0; }
   static bool supports_cmov()         { return (_features & CPU_CMOV) != 0; }
@@ -703,6 +703,11 @@ class VM_Version : public Abstract_VM_Version {
   static bool supports_cet_ss()       { return (_features & CPU_CET_SS) != 0; }
   static bool supports_cet_ibt()      { return (_features & CPU_CET_IBT) != 0; }
 
+  //
+  // Feature identification not affected by VM flags
+  //
+  static bool cpu_supports_evex()         { return (_cpu_features & CPU_AVX512F) != 0; }
+
   // Intel features
   static bool is_intel_family_core() { return is_intel() &&
                                        extended_cpu_family() == CPU_FAMILY_INTEL_CORE; }
diff --git a/src/hotspot/share/runtime/abstract_vm_version.hpp b/src/hotspot/share/runtime/abstract_vm_version.hpp
index d8ffca8de81..05675cc683a 100644
--- a/src/hotspot/share/runtime/abstract_vm_version.hpp
+++ b/src/hotspot/share/runtime/abstract_vm_version.hpp
@@ -54,10 +54,13 @@ class Abstract_VM_Version: AllStatic {
   static const char*  _s_vm_release;
   static const char*  _s_internal_vm_info_string;
 
-  // CPU feature flags.
+  // CPU feature flags which can be restricted by VM flags.
   static uint64_t _features;
   static const char* _features_string;
 
+  // CPU feature flags not affected by VM flags.
+  static uint64_t _cpu_features;
+
   // These are set by machine-dependent initializations
 #ifndef SUPPORTS_NATIVE_CX8
   static bool         _supports_cx8;

rkennke · 2024-01-29T09:23:20Z

/contributor add @vnkozlov

openjdk · 2024-01-29T09:23:58Z

@rkennke
Contributor Vladimir Kozlov <kvn@openjdk.org> successfully added.

rkennke · 2024-01-29T09:24:24Z

VM_Version could distinguish between CPU features that are supported by the CPU
We can start with just EVEX check. It is not big change:

$ git diff
diff --git a/src/hotspot/cpu/x86/vm_version_x86.cpp b/src/hotspot/cpu/x86/vm_version_x86.cpp
index df1ea6edd30..8b4ca442b5a 100644
--- a/src/hotspot/cpu/x86/vm_version_x86.cpp
+++ b/src/hotspot/cpu/x86/vm_version_x86.cpp
@@ -809,7 +809,8 @@ void VM_Version::get_processor_features() {
   _stepping = cpu_stepping();
 
   if (cpu_family() > 4) { // it supports CPUID
-    _features = feature_flags();
+    _features = feature_flags(); // It can be changed by VM flags
+    _cpu_features = _features;   // Preserve features
     // Logical processors are only available on P4s and above,
     // and only if hyperthreading is available.
     _logical_processors_per_package = logical_processor_count();
diff --git a/src/hotspot/cpu/x86/vm_version_x86.hpp b/src/hotspot/cpu/x86/vm_version_x86.hpp
index e521a6ee3bc..de86ce51541 100644
--- a/src/hotspot/cpu/x86/vm_version_x86.hpp
+++ b/src/hotspot/cpu/x86/vm_version_x86.hpp
@@ -640,7 +640,7 @@ class VM_Version : public Abstract_VM_Version {
   }
 
   //
-  // Feature identification
+  // Feature identification which can be affected by VM flags
   //
   static bool supports_cpuid()        { return _features  != 0; }
   static bool supports_cmov()         { return (_features & CPU_CMOV) != 0; }
@@ -703,6 +703,11 @@ class VM_Version : public Abstract_VM_Version {
   static bool supports_cet_ss()       { return (_features & CPU_CET_SS) != 0; }
   static bool supports_cet_ibt()      { return (_features & CPU_CET_IBT) != 0; }
 
+  //
+  // Feature identification not affected by VM flags
+  //
+  static bool cpu_supports_evex()         { return (_cpu_features & CPU_AVX512F) != 0; }
+
   // Intel features
   static bool is_intel_family_core() { return is_intel() &&
                                        extended_cpu_family() == CPU_FAMILY_INTEL_CORE; }
diff --git a/src/hotspot/share/runtime/abstract_vm_version.hpp b/src/hotspot/share/runtime/abstract_vm_version.hpp
index d8ffca8de81..05675cc683a 100644
--- a/src/hotspot/share/runtime/abstract_vm_version.hpp
+++ b/src/hotspot/share/runtime/abstract_vm_version.hpp
@@ -54,10 +54,13 @@ class Abstract_VM_Version: AllStatic {
   static const char*  _s_vm_release;
   static const char*  _s_internal_vm_info_string;
 
-  // CPU feature flags.
+  // CPU feature flags which can be restricted by VM flags.
   static uint64_t _features;
   static const char* _features_string;
 
+  // CPU feature flags not affected by VM flags.
+  static uint64_t _cpu_features;
+
   // These are set by machine-dependent initializations
 #ifndef SUPPORTS_NATIVE_CX8
   static bool         _supports_cx8;

Nice, thank you! That works (with some minor modification). I've changed the PR from removing the assert to relaxing it to CPU feature check.

vnkozlov

Good. I will submit our testing before approval.
And this needs second review.

shipilev

This looks fine, with nits.

/reviewers 2

src/hotspot/cpu/x86/vm_version_x86.hpp

src/hotspot/cpu/x86/vm_version_x86.cpp

src/hotspot/cpu/x86/vm_version_x86.hpp

src/hotspot/share/runtime/abstract_vm_version.hpp

openjdk · 2024-01-29T18:36:41Z

@rkennke This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8324734: Relax too-strict assert(VM_Version::supports_evex()) in Assembler::locate_operand()

Co-authored-by: Vladimir Kozlov <kvn@openjdk.org>
Reviewed-by: kvn, shade

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 33 new commits pushed to the master branch:

fd8adf3: 8324856: Serial: Move Generation::is_in to DefNewGeneration
a1d65eb: 8324125: Improve class initialization barrier in TemplateTable::_new for RISC-V
b6d364a: 8324865: windows-x64-slowdebug still does not build after JDK-8324840
64c3642: 8242564: javadoc crashes:: class cast exception com.sun.tools.javac.code.Symtab$6
e999dfc: 8323503: x86: Shorter movptr(reg, imm) for 32-bit unsigned immediates
84deeb6: 8324667: fold Parse::seems_stable_comparison()
fb07bbe: 8324717: Remove HotSpotJVMCICompilerFactory
d1e6763: 8324733: [macos14] Problem list tests which fail due to macOS bug described in JDK-8322653
c1281e6: 8324678: Replace NULL with nullptr in HotSpot gtests
a6bdee4: 8324681: Replace NULL with nullptr in HotSpot jtreg test native code files
... and 23 more: https://git.openjdk.org/jdk/compare/62b3293df0442b06cd00488774db7b608baca774...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

openjdk · 2024-01-29T18:36:46Z

@shipilev
The total number of required reviews for this PR (including the jcheck configuration and the last /reviewers command) is now set to 2 (with at least 1 Reviewer, 1 Author).

Co-authored-by: Aleksey Shipilëv <shipilev@amazon.de>

rkennke · 2024-01-29T18:42:21Z

This looks fine, with nits.

Thanks for the review! I fixed all the mentioned issues.

vnkozlov

My testing passed.

shipilev

Looks fine to me.

rkennke · 2024-01-30T10:47:07Z

Thanks, Vladimir and Aleksey!

/intergrate

openjdk · 2024-01-30T10:47:58Z

@rkennke Unknown command intergrate - for a list of valid commands use /help.

rkennke · 2024-01-30T13:24:59Z

/integrate

openjdk · 2024-01-30T13:26:11Z

Going to push as commit f0024f5.
Since your change was applied there have been 33 commits pushed to the master branch:

fd8adf3: 8324856: Serial: Move Generation::is_in to DefNewGeneration
a1d65eb: 8324125: Improve class initialization barrier in TemplateTable::_new for RISC-V
b6d364a: 8324865: windows-x64-slowdebug still does not build after JDK-8324840
64c3642: 8242564: javadoc crashes:: class cast exception com.sun.tools.javac.code.Symtab$6
e999dfc: 8323503: x86: Shorter movptr(reg, imm) for 32-bit unsigned immediates
84deeb6: 8324667: fold Parse::seems_stable_comparison()
fb07bbe: 8324717: Remove HotSpotJVMCICompilerFactory
d1e6763: 8324733: [macos14] Problem list tests which fail due to macOS bug described in JDK-8322653
c1281e6: 8324678: Replace NULL with nullptr in HotSpot gtests
a6bdee4: 8324681: Replace NULL with nullptr in HotSpot jtreg test native code files
... and 23 more: https://git.openjdk.org/jdk/compare/62b3293df0442b06cd00488774db7b608baca774...master

Your commit was automatically rebased without conflicts.

openjdk · 2024-01-30T13:26:17Z

@rkennke Pushed as commit f0024f5.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

8324734: Remove too-strict assert(VM_Version::supports_evex()) in Ass…

1788055

…embler::locate_operand()

openjdk bot added the rfr Pull request is ready for review label Jan 26, 2024

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vnkozlov reviewed Jan 26, 2024

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Distinguish between CPU and HotSpot features for supports_evex()

f392938

rkennke changed the title ~~8324734: Remove too-strict assert(VM_Version::supports_evex()) in Assembler::locate_operand()~~ 8324734: Relax too-strict assert(VM_Version::supports_evex()) in Assembler::locate_operand() Jan 29, 2024

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rkennke and others added 5 commits January 29, 2024 19:39

Update src/hotspot/cpu/x86/vm_version_x86.cpp

770fc02

Co-authored-by: Aleksey Shipilëv <shipilev@amazon.de>

Update src/hotspot/cpu/x86/vm_version_x86.hpp

16a8f23

Co-authored-by: Aleksey Shipilëv <shipilev@amazon.de>

Update src/hotspot/share/runtime/abstract_vm_version.hpp

0d9f938

Co-authored-by: Aleksey Shipilëv <shipilev@amazon.de>

Update src/hotspot/share/runtime/abstract_vm_version.hpp

179a4b5

Co-authored-by: Aleksey Shipilëv <shipilev@amazon.de>

Fix intendation

856cbfa

vnkozlov approved these changes Jan 29, 2024

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jatin-bhateja mentioned this pull request Apr 10, 2025

8352675: Support Intel AVX10 converged vector ISA feature detection #24329

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8324734: Relax too-strict assert(VM_Version::supports_evex()) in Assembler::locate_operand() #17590

8324734: Relax too-strict assert(VM_Version::supports_evex()) in Assembler::locate_operand() #17590

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