#923: cstack=vm support for JDK 23+

apangin · apangin · commit 34a9e1354a66 · 2024-05-24T01:57:00.000+01:00
diff --git a/src/profiler.cpp b/src/profiler.cpp
@@ -1124,11 +1124,8 @@ Error Profiler::start(Arguments& args, bool reset) {
         return Error("DWARF unwinding is not supported on this platform");
     } else if (_cstack == CSTACK_LBR && _engine != &perf_events) {
         return Error("Branch stack is supported only with PMU events");
-    } else if (_cstack == CSTACK_VM) {
-        if (!VMStructs::hasStackStructs()) {
-            return Error("VMStructs stack walking is not supported on this JVM/platform");
-        }
-        Log::info("cstack=vm is an experimental option, use with care");
+    } else if (_cstack == CSTACK_VM && !VMStructs::hasStackStructs()) {
+        return Error("VMStructs stack walking is not supported on this JVM/platform");
     }
 
     // Kernel symbols are useful only for perf_events without --all-user
diff --git a/src/vmStructs.cpp b/src/vmStructs.cpp
@@ -465,12 +465,17 @@ void VMStructs::resolveOffsets() {
         _call_stub_return = *_call_stub_return_addr;
     }
 
+    // Since JDK 23, _metadata_offset is relative to _data_offset. See metadata()
+    if (_nmethod_immutable_offset < 0) {
+        _data_offset = 0;
+    }
+
     _has_stack_structs = _has_method_structs
             && _interpreter_frame_bcp_offset != 0
             && _code_offset != -1
+            && _data_offset >= 0
             && _scopes_data_offset != -1
             && _scopes_pcs_offset >= 0
-            && _nmethod_immutable_offset < 0  // TODO: not yet supported
             && _nmethod_metadata_offset >= 0
             && _thread_vframe_offset >= 0
             && _thread_exception_offset >= 0
@@ -677,8 +682,8 @@ int NMethod::findScopeOffset(const void* pc) {
     }
 
     const int* scopes_pcs = (const int*) at(_scopes_pcs_offset);
-    PcDesc* pcd = (PcDesc*) at(scopes_pcs[0]);
-    PcDesc* pcd_end = (PcDesc*) at(scopes_pcs[1]);
+    PcDesc* pcd = (PcDesc*) immutableDataAt(scopes_pcs[0]);
+    PcDesc* pcd_end = (PcDesc*) immutableDataAt(scopes_pcs[1]);
     int low = 0;
     int high = (pcd_end - pcd) - 1;
 
diff --git a/src/vmStructs.h b/src/vmStructs.h
@@ -396,9 +396,20 @@ class NMethod : VMStructs {
         return *(short*) at(_frame_complete_offset);
     }
 
-    // TODO: offset is short on JDK 23+
     void setFrameCompleteOffset(int offset) {
-        *(int*) at(_frame_complete_offset) = offset;
+        if (_nmethod_immutable_offset > 0) {
+            // _frame_complete_offset is short on JDK 23+
+            *(short*) at(_frame_complete_offset) = offset;
+        } else {
+            *(int*) at(_frame_complete_offset) = offset;
+        }
+    }
+
+    const char* immutableDataAt(int offset) {
+        if (_nmethod_immutable_offset > 0) {
+            return *(const char**) at(_nmethod_immutable_offset) + offset;
+        }
+        return at(offset);
     }
 
     const char* code() {
@@ -411,7 +422,7 @@ class NMethod : VMStructs {
 
     const char* scopes() {
         if (_scopes_data_offset > 0) {
-            return at(*(int*) at(_scopes_data_offset));
+            return immutableDataAt(*(int*) at(_scopes_data_offset));
         } else {
             return *(const char**) at(-_scopes_data_offset);
         }
@@ -464,6 +475,9 @@ class NMethod : VMStructs {
     }
 
     VMMethod** metadata() {
+        if (_data_offset > 0) {
+            return (VMMethod**) at(*(int*) at(_data_offset) + *(unsigned short*) at(_nmethod_metadata_offset));
+        }
         return (VMMethod**) at(*(int*) at(_nmethod_metadata_offset));
     }
 
@@ -556,27 +570,30 @@ class PcDesc {
 
 class ScopeDesc : VMStructs {
   private:
-    NMethod* _nm;
+    const unsigned char* _scopes;
+    VMMethod** _metadata;
     const unsigned char* _stream;
     int _method_offset;
     int _bci;
 
     int readInt();
 
   public:
-    ScopeDesc(NMethod* nm) : _nm(nm) {
+    ScopeDesc(NMethod* nm) {
+        _scopes = (const unsigned char*)nm->scopes();
+        _metadata = nm->metadata();
     }
 
     int decode(int offset) {
-        _stream = (const unsigned char*)_nm->scopes() + offset;
+        _stream = _scopes + offset;
         int sender_offset = readInt();
         _method_offset = readInt();
         _bci = readInt() - 1;
         return sender_offset;
     }
 
     VMMethod* method() {
-        return _method_offset > 0 ? _nm->metadata()[_method_offset - 1] : NULL;
+        return _method_offset > 0 ? _metadata[_method_offset - 1] : NULL;
     }
 
     int bci() {
