#914: Do not set DebugNonSafepoints, if it is already set in the Command Line

Author: apangin

src/vmEntry.cpp

@@ -216,17 +216,17 @@ bool VM::init(JavaVM* vm, bool attach) {
     } else {
         // DebugNonSafepoints is automatically enabled with CompiledMethodLoad,
         // otherwise we set the flag manually
-        char* flag_addr = (char*)JVMFlag::find("DebugNonSafepoints");
-        if (flag_addr != NULL) {
-            *flag_addr = 1;
+        JVMFlag* f = JVMFlag::find("DebugNonSafepoints");
+        if (f != NULL && f->origin() == 0) {
+            f->set(1);
         }
     }
 
     if (_can_sample_objects) {
         // SetHeapSamplingInterval does not have immediate effect, so apply the configuration
         // as early as possible to allow profiling all startup allocations
-        char* use_tlab = (char*)JVMFlag::find("UseTLAB");
-        if (use_tlab != NULL && *use_tlab == 0) {
+        JVMFlag* f = JVMFlag::find("UseTLAB");
+        if (f != NULL && !f->get()) {
             _jvmti->SetHeapSamplingInterval(0);
         }
     }

src/vmStructs.cpp

@@ -72,6 +72,7 @@ int VMStructs::_vs_low_offset = -1;
 int VMStructs::_vs_high_offset = -1;
 int VMStructs::_flag_name_offset = -1;
 int VMStructs::_flag_addr_offset = -1;
+int VMStructs::_flag_origin_offset = -1;
 const char* VMStructs::_flags_addr = NULL;
 int VMStructs::_flag_count = 0;
 int VMStructs::_flag_size = 0;
@@ -335,6 +336,8 @@ void VMStructs::initOffsets() {
                     _flag_name_offset = *(int*)(entry + offset_offset);
                 } else if (strcmp(field, "_addr") == 0 || strcmp(field, "addr") == 0) {
                     _flag_addr_offset = *(int*)(entry + offset_offset);
+                } else if (strcmp(field, "_flags") == 0 || strcmp(field, "origin") == 0) {
+                    _flag_origin_offset = *(int*)(entry + offset_offset);
                 } else if (strcmp(field, "flags") == 0) {
                     _flags_addr = **(char***)(entry + address_offset);
                 } else if (strcmp(field, "numFlags") == 0) {
@@ -396,14 +399,14 @@ void VMStructs::resolveOffsets() {
         _klass = (jfieldID)(uintptr_t)(*_klass_offset_addr << 2 | 2);
     }
 
-    char* ccp = (char*)JVMFlag::find("UseCompressedClassPointers");
-    if (ccp != NULL && *ccp && _narrow_klass_base_addr != NULL && _narrow_klass_shift_addr != NULL) {
+    JVMFlag* ccp = JVMFlag::find("UseCompressedClassPointers");
+    if (ccp != NULL && ccp->get() && _narrow_klass_base_addr != NULL && _narrow_klass_shift_addr != NULL) {
         _narrow_klass_base = *_narrow_klass_base_addr;
         _narrow_klass_shift = *_narrow_klass_shift_addr;
     }
 
-    char* coh = (char*)JVMFlag::find("UseCompactObjectHeaders");
-    if (coh != NULL && *coh) {
+    JVMFlag* coh = JVMFlag::find("UseCompactObjectHeaders");
+    if (coh != NULL && coh->get()) {
         _compact_object_headers = true;
     }
 
@@ -644,12 +647,12 @@ NMethod* CodeHeap::findNMethod(char* heap, const void* pc) {
     return block[sizeof(size_t)] ? (NMethod*)(block + 2 * sizeof(size_t)) : NULL;
 }
 
-void* JVMFlag::find(const char* name) {
+JVMFlag* JVMFlag::find(const char* name) {
     if (_flags_addr != NULL && _flag_size > 0) {
         for (int i = 0; i < _flag_count; i++) {
             JVMFlag* f = (JVMFlag*)(_flags_addr + i * _flag_size);
-            if (f->name() != NULL && strcmp(f->name(), name) == 0) {
-                return f->addr();
+            if (f->name() != NULL && strcmp(f->name(), name) == 0 && f->addr() != NULL) {
+                return f;
             }
         }
     }

src/vmStructs.h

@@ -77,6 +77,7 @@ class VMStructs {
     static int _vs_high_offset;
     static int _flag_name_offset;
     static int _flag_addr_offset;
+    static int _flag_origin_offset;
     static const char* _flags_addr;
     static int _flag_count;
     static int _flag_size;
@@ -510,14 +511,26 @@ class CollectedHeap : VMStructs {
 
 class JVMFlag : VMStructs {
   public:
-    static void* find(const char* name);
+    static JVMFlag* find(const char* name);
 
     const char* name() {
         return *(const char**) at(_flag_name_offset);
     }
 
-    void* addr() {
-        return *(void**) at(_flag_addr_offset);
+    char* addr() {
+        return *(char**) at(_flag_addr_offset);
+    }
+
+    char origin() {
+        return _flag_origin_offset >= 0 ? (*(char*) at(_flag_origin_offset)) & 15 : 0;
+    }
+
+    char get() {
+        return *addr();
+    }
+
+    void set(char value) {
+        *addr() = value;
     }
 };