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8227680: FastJNIAccessors: Check for JVMTI field access event requests at runtime

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Check JvmtiExport::_field_access_count != 0 at runtime

Reviewed-by: dholmes, eosterlund, bulasevich
This commit is contained in:
Martin Doerr 2019-07-29 18:22:55 +02:00
parent 62c2d1fbd9
commit 70fb85adc5
8 changed files with 401 additions and 41 deletions
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54
src/hotspot/cpu/aarch64/jniFastGetField_aarch64.cpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2004, 2017, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2004, 2019, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2014, Red Hat Inc. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
@ -79,33 +79,57 @@ address JNI_FastGetField::generate_fast_get_int_field0(BasicType type) {
Address safepoint_counter_addr(rcounter_addr, offset);
__ ldrw(rcounter, safepoint_counter_addr);
__ tbnz(rcounter, 0, slow);
__ eor(robj, c_rarg1, rcounter);
__ eor(robj, robj, rcounter); // obj, since
// robj ^ rcounter ^ rcounter == robj
// robj is address dependent on rcounter.
if (!UseBarriersForVolatile) {
// Field may be volatile. See other usages of this flag.
__ membar(MacroAssembler::AnyAny);
__ mov(robj, c_rarg1);
} else if (JvmtiExport::can_post_field_access()) {
// Using barrier to order wrt. JVMTI check and load of result.
__ membar(Assembler::LoadLoad);
__ mov(robj, c_rarg1);
} else {
// Using address dependency to order wrt. load of result.
__ eor(robj, c_rarg1, rcounter);
__ eor(robj, robj, rcounter); // obj, since
// robj ^ rcounter ^ rcounter == robj
// robj is address dependent on rcounter.
}
if (JvmtiExport::can_post_field_access()) {
// Check to see if a field access watch has been set before we
// take the fast path.
unsigned long offset2;
__ adrp(result,
ExternalAddress((address) JvmtiExport::get_field_access_count_addr()),
offset2);
__ ldrw(result, Address(result, offset2));
__ cbnzw(result, slow);
}
// Both robj and rscratch1 are clobbered by try_resolve_jobject_in_native.
BarrierSetAssembler* bs = BarrierSet::barrier_set()->barrier_set_assembler();
bs->try_resolve_jobject_in_native(masm, c_rarg0, robj, rscratch1, slow);
__ lsr(roffset, c_rarg2, 2); // offset
__ add(result, robj, roffset);
assert(count < LIST_CAPACITY, "LIST_CAPACITY too small");
speculative_load_pclist[count] = __ pc(); // Used by the segfault handler
// Using acquire: Order JVMTI check and load of result wrt. succeeding check
// (LoadStore for volatile field).
switch (type) {
case T_BOOLEAN: __ ldrb (result, Address(robj, roffset)); break;
case T_BYTE: __ ldrsb (result, Address(robj, roffset)); break;
case T_CHAR: __ ldrh (result, Address(robj, roffset)); break;
case T_SHORT: __ ldrsh (result, Address(robj, roffset)); break;
case T_FLOAT: __ ldrw (result, Address(robj, roffset)); break;
case T_INT: __ ldrsw (result, Address(robj, roffset)); break;
case T_BOOLEAN: __ ldarb(result, result); break;
case T_BYTE: __ ldarb(result, result); __ sxtb(result, result); break;
case T_CHAR: __ ldarh(result, result); break;
case T_SHORT: __ ldarh(result, result); __ sxth(result, result); break;
case T_FLOAT: __ ldarw(result, result); break;
case T_INT: __ ldarw(result, result); __ sxtw(result, result); break;
case T_DOUBLE:
case T_LONG: __ ldr (result, Address(robj, roffset)); break;
case T_LONG: __ ldar (result, result); break;
default: ShouldNotReachHere();
}
// counter_addr is address dependent on result.
__ eor(rcounter_addr, rcounter_addr, result);
__ eor(rcounter_addr, rcounter_addr, result);
__ ldrw(rscratch1, safepoint_counter_addr);
__ cmpw(rcounter, rscratch1);
__ br (Assembler::NE, slow);

42
src/hotspot/cpu/arm/jniFastGetField_arm.cpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2008, 2018, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2008, 2019, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -32,7 +32,7 @@
#define __ masm->
#define BUFFER_SIZE 96
#define BUFFER_SIZE 120
address JNI_FastGetField::generate_fast_get_int_field0(BasicType type) {
const char* name = NULL;
@ -99,10 +99,10 @@ address JNI_FastGetField::generate_fast_get_int_field0(BasicType type) {
CodeBuffer cbuf(blob);
MacroAssembler* masm = new MacroAssembler(&cbuf);
fast_entry = __ pc();
Label slow_case;
// Safepoint check
InlinedAddress safepoint_counter_addr(SafepointSynchronize::safepoint_counter_addr());
Label slow_case;
__ ldr_literal(Rsafepoint_counter_addr, safepoint_counter_addr);
__ push(RegisterSet(R0, R3)); // save incoming arguments for slow case
@ -112,9 +112,21 @@ address JNI_FastGetField::generate_fast_get_int_field0(BasicType type) {
__ bic(R1, R1, JNIHandles::weak_tag_mask);
// Address dependency restricts memory access ordering. It's cheaper than explicit LoadLoad barrier
__ andr(Rtmp1, Rsafept_cnt, (unsigned)1);
__ ldr(Robj, Address(R1, Rtmp1));
if (JvmtiExport::can_post_field_access()) {
// Using barrier to order wrt. JVMTI check and load of result.
__ membar(MacroAssembler::Membar_mask_bits(MacroAssembler::LoadLoad), Rtmp1);
// Check to see if a field access watch has been set before we
// take the fast path.
__ ldr_global_s32(Rtmp1, (address)JvmtiExport::get_field_access_count_addr());
__ cbnz(Rtmp1, slow_case);
__ ldr(Robj, Address(R1));
} else {
// Address dependency restricts memory access ordering. It's cheaper than explicit LoadLoad barrier
__ andr(Rtmp1, Rsafept_cnt, (unsigned)1);
__ ldr(Robj, Address(R1, Rtmp1));
}
Address field_addr;
if (type != T_BOOLEAN
@ -170,20 +182,18 @@ address JNI_FastGetField::generate_fast_get_int_field0(BasicType type) {
ShouldNotReachHere();
}
// Address dependency restricts memory access ordering. It's cheaper than explicit LoadLoad barrier
__ ldr_literal(Rsafepoint_counter_addr, safepoint_counter_addr);
#ifdef __ABI_HARD__
if (type == T_FLOAT || type == T_DOUBLE) {
__ ldr_literal(Rsafepoint_counter_addr, safepoint_counter_addr);
__ fmrrd(Rres, Rres_hi, D0);
__ eor(Rtmp2, Rres, Rres);
__ ldr_s32(Rsafept_cnt2, Address(Rsafepoint_counter_addr, Rtmp2));
} else
#endif // __ABI_HARD__
{
__ ldr_literal(Rsafepoint_counter_addr, safepoint_counter_addr);
__ eor(Rtmp2, Rres, Rres);
__ ldr_s32(Rsafept_cnt2, Address(Rsafepoint_counter_addr, Rtmp2));
}
#endif // __ABI_HARD__
// Order JVMTI check and load of result wrt. succeeding check
// (LoadStore for volatile field).
__ membar(MacroAssembler::Membar_mask_bits(MacroAssembler::LoadLoad | MacroAssembler::LoadStore), Rtmp2);
__ ldr_s32(Rsafept_cnt2, Address(Rsafepoint_counter_addr));
__ cmp(Rsafept_cnt2, Rsafept_cnt);
// discards saved R0 R1 R2 R3
__ add(SP, SP, 4 * wordSize, eq);

29
src/hotspot/cpu/sparc/jniFastGetField_sparc.cpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2004, 2017, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2004, 2019, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -70,6 +70,15 @@ address JNI_FastGetField::generate_fast_get_int_field0(BasicType type) {
__ andcc (G4, 1, G0);
__ br (Assembler::notZero, false, Assembler::pn, label1);
__ delayed()->srl (O2, 2, O4);
if (JvmtiExport::can_post_field_access()) {
// Check to see if a field access watch has been set before we
// take the fast path.
AddressLiteral get_field_access_count_addr(JvmtiExport::get_field_access_count_addr());
__ load_contents(get_field_access_count_addr, O5);
__ cmp_and_br_short(O5, 0, Assembler::notEqual, Assembler::pn, label1);
}
__ mov(O1, O5);
// Both O5 and G3 are clobbered by try_resolve_jobject_in_native.
@ -153,6 +162,15 @@ address JNI_FastGetField::generate_fast_get_long_field() {
__ andcc (G4, 1, G0);
__ br (Assembler::notZero, false, Assembler::pn, label1);
__ delayed()->srl (O2, 2, O4);
if (JvmtiExport::can_post_field_access()) {
// Check to see if a field access watch has been set before we
// take the fast path.
AddressLiteral get_field_access_count_addr(JvmtiExport::get_field_access_count_addr());
__ load_contents(get_field_access_count_addr, O5);
__ cmp_and_br_short(O5, 0, Assembler::notEqual, Assembler::pn, label1);
}
__ mov(O1, O5);
// Both O5 and G1 are clobbered by try_resolve_jobject_in_native.
@ -211,6 +229,15 @@ address JNI_FastGetField::generate_fast_get_float_field0(BasicType type) {
__ andcc (G4, 1, G0);
__ br (Assembler::notZero, false, Assembler::pn, label1);
__ delayed()->srl (O2, 2, O4);
if (JvmtiExport::can_post_field_access()) {
// Check to see if a field access watch has been set before we
// take the fast path.
AddressLiteral get_field_access_count_addr(JvmtiExport::get_field_access_count_addr());
__ load_contents(get_field_access_count_addr, O5);
__ cmp_and_br_short(O5, 0, Assembler::notEqual, Assembler::pn, label1);
}
__ mov(O1, O5);
// Both O5 and G3 are clobbered by try_resolve_jobject_in_native.

26
src/hotspot/cpu/x86/jniFastGetField_x86_32.cpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2004, 2017, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2004, 2019, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -75,6 +75,14 @@ address JNI_FastGetField::generate_fast_get_int_field0(BasicType type) {
__ mov32 (rcx, counter);
__ testb (rcx, 1);
__ jcc (Assembler::notZero, slow);
if (JvmtiExport::can_post_field_access()) {
// Check to see if a field access watch has been set before we
// take the fast path.
__ cmp32(ExternalAddress((address) JvmtiExport::get_field_access_count_addr()), 0);
__ jcc(Assembler::notZero, slow);
}
__ mov(rax, rcx);
__ andptr(rax, 1); // rax, must end up 0
__ movptr(rdx, Address(rsp, rax, Address::times_1, 2*wordSize));
@ -188,6 +196,14 @@ address JNI_FastGetField::generate_fast_get_long_field() {
__ mov32 (rcx, counter);
__ testb (rcx, 1);
__ jcc (Assembler::notZero, slow);
if (JvmtiExport::can_post_field_access()) {
// Check to see if a field access watch has been set before we
// take the fast path.
__ cmp32(ExternalAddress((address) JvmtiExport::get_field_access_count_addr()), 0);
__ jcc(Assembler::notZero, slow);
}
__ mov(rax, rcx);
__ andptr(rax, 1); // rax, must end up 0
__ movptr(rdx, Address(rsp, rax, Address::times_1, 3*wordSize));
@ -272,6 +288,14 @@ address JNI_FastGetField::generate_fast_get_float_field0(BasicType type) {
__ mov32 (rcx, counter);
__ testb (rcx, 1);
__ jcc (Assembler::notZero, slow);
if (JvmtiExport::can_post_field_access()) {
// Check to see if a field access watch has been set before we
// take the fast path.
__ cmp32(ExternalAddress((address) JvmtiExport::get_field_access_count_addr()), 0);
__ jcc(Assembler::notZero, slow);
}
__ mov(rax, rcx);
__ andptr(rax, 1); // rax, must end up 0
__ movptr(rdx, Address(rsp, rax, Address::times_1, 2*wordSize));

27
src/hotspot/cpu/x86/jniFastGetField_x86_64.cpp
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@ -1,5 +1,5 @@
/*
* Copyright (c) 2004, 2017, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2004, 2019, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@ -41,11 +41,10 @@
// c_rarg1: obj
// c_rarg2: jfield id
static const Register rtmp = r8;
static const Register robj = r9;
static const Register rcounter = r10;
static const Register roffset = r11;
static const Register rcounter_addr = r11;
static const Register rtmp = rax; // r8 == c_rarg2 on Windows
static const Register robj = r9;
static const Register roffset = r10;
static const Register rcounter = r11;
// Warning: do not use rip relative addressing after the first counter load
// since that may scratch r10!
@ -74,6 +73,15 @@ address JNI_FastGetField::generate_fast_get_int_field0(BasicType type) {
__ mov (robj, c_rarg1);
__ testb (rcounter, 1);
__ jcc (Assembler::notZero, slow);
if (JvmtiExport::can_post_field_access()) {
// Check to see if a field access watch has been set before we
// take the fast path.
assert_different_registers(rscratch1, robj, rcounter); // cmp32 clobbers rscratch1!
__ cmp32(ExternalAddress((address) JvmtiExport::get_field_access_count_addr()), 0);
__ jcc(Assembler::notZero, slow);
}
__ mov (roffset, c_rarg2);
__ shrptr(roffset, 2); // offset
@ -164,6 +172,13 @@ address JNI_FastGetField::generate_fast_get_float_field0(BasicType type) {
__ testb (rcounter, 1);
__ jcc (Assembler::notZero, slow);
if (JvmtiExport::can_post_field_access()) {
// Check to see if a field access watch has been set before we
// take the fast path.
__ cmp32(ExternalAddress((address) JvmtiExport::get_field_access_count_addr()), 0);
__ jcc(Assembler::notZero, slow);
}
// Both robj and rtmp are clobbered by try_resolve_jobject_in_native.
BarrierSetAssembler* bs = BarrierSet::barrier_set()->barrier_set_assembler();
bs->try_resolve_jobject_in_native(masm, /* jni_env */ c_rarg0, robj, rtmp, slow);

3
src/hotspot/share/prims/jni.cpp
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@ -3776,8 +3776,7 @@ void copy_jni_function_table(const struct JNINativeInterface_ *new_jni_NativeInt
void quicken_jni_functions() {
// Replace Get<Primitive>Field with fast versions
if (UseFastJNIAccessors && !JvmtiExport::can_post_field_access()
&& !VerifyJNIFields && !CountJNICalls && !CheckJNICalls) {
if (UseFastJNIAccessors && !VerifyJNIFields && !CountJNICalls && !CheckJNICalls) {
address func;
func = JNI_FastGetField::generate_fast_get_boolean_field();
if (func != (address)-1) {

124
test/hotspot/jtreg/runtime/jni/FastGetField/FastGetField.java Normal file
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@ -0,0 +1,124 @@
/*
* Copyright (c) 2019 SAP SE and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
/**
* @test
* @bug 8227680
* @summary Tests that all FieldAccess notifications for Get*Field
with primitive type are generated.
* @compile FastGetField.java
* @run main/othervm/native -agentlib:FastGetField -XX:+IgnoreUnrecognizedVMOptions -XX:-VerifyJNIFields FastGetField
* @run main/othervm/native -agentlib:FastGetField -XX:+IgnoreUnrecognizedVMOptions -XX:-VerifyJNIFields -XX:+UnlockDiagnosticVMOptions -XX:+ForceUnreachable -XX:+SafepointALot -XX:GuaranteedSafepointInterval=1 FastGetField
*/
import java.lang.reflect.Field;
public class FastGetField {
private static final String agentLib = "FastGetField";
private native boolean initFieldIDs(Class c);
private native boolean initWatchers(Class c);
public native long accessFields(MyItem i);
public static native long getFieldAccessCount();
static final int loop_cnt = 10000;
class MyItem {
// Names should match JNI types.
boolean Z;
byte B;
short S;
char C;
int I;
long J;
float F;
double D;
public void change_values() {
Z = true;
B = 1;
C = 1;
S = 1;
I = 1;
J = 1l;
F = 1.0f;
D = 1.0;
}
public void reset_values() {
Z = false;
B = 0;
C = 0;
S = 0;
I = 0;
J = 0l;
F = 0.0f;
D = 0.0;
}
}
// Static initialization.
static {
try {
System.loadLibrary(agentLib);
} catch (UnsatisfiedLinkError ex) {
System.err.println("Failed to load " + agentLib + " lib");
System.err.println("java.library.path: " + System.getProperty("java.library.path"));
throw ex;
}
}
public void TestFieldAccess() throws Exception {
MyItem i = new MyItem();
if (!initFieldIDs(MyItem.class)) throw new RuntimeException("FieldID initialization failed!");
long duration = System.nanoTime();
for (int c = 0; c < loop_cnt; ++c) {
if (accessFields(i) != 0l) throw new RuntimeException("Wrong initial result!");
i.change_values();
if (accessFields(i) != 8l) throw new RuntimeException("Wrong result after changing!");
i.reset_values();
}
duration = System.nanoTime() - duration;
System.out.println(loop_cnt + " iterations took " + duration + "ns.");
if (getFieldAccessCount() != 0) throw new RuntimeException("Watch not yet active!");
// Install watchers.
if (!initWatchers(MyItem.class)) throw new RuntimeException("JVMTI missing!");
// Try again with watchers.
if (accessFields(i) != 0l) throw new RuntimeException("Wrong initial result!");
i.change_values();
if (accessFields(i) != 8l) throw new RuntimeException("Wrong result after changing!");
if (getFieldAccessCount() != 16) throw new RuntimeException("Unexpected event count!");
}
public static void main(String[] args) throws Exception {
FastGetField inst = new FastGetField();
inst.TestFieldAccess();
}
}

137
test/hotspot/jtreg/runtime/jni/FastGetField/libFastGetField.c Normal file
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@ -0,0 +1,137 @@
/*
* Copyright (c) 2019 SAP SE and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
#include <stdio.h>
#include <string.h>
#include "jvmti.h"
static jvmtiEnv *jvmti = NULL;
static const char* fields[] = { "Z", "B", "C", "S", "I", "J", "F", "D" };
#define NUM_FIELDS (sizeof fields / sizeof fields[0])
static jfieldID fieldIDs[NUM_FIELDS];
static jlong fieldAccessCount = 0;
JNIEXPORT jboolean JNICALL Java_FastGetField_initFieldIDs(JNIEnv *env, jobject this, jclass c) {
for (int i = 0; i < (int)NUM_FIELDS; ++i) {
fieldIDs[i] = (*env)->GetFieldID(env, c, fields[i], fields[i]);
if (fieldIDs[i] == NULL) {
printf("field %d not found\n", i);
return JNI_FALSE;
}
}
return JNI_TRUE;
}
JNIEXPORT jboolean JNICALL Java_FastGetField_initWatchers(JNIEnv *env, jobject this, jclass c) {
if (jvmti == NULL) {
printf("jvmti is NULL\n");
return JNI_FALSE;
}
for (int i = 0; i < (int)NUM_FIELDS; ++i) {
jvmtiError err = (*jvmti)->SetFieldAccessWatch(jvmti, c, fieldIDs[i]);
if (err != JVMTI_ERROR_NONE) {
printf("SetFieldAccessWatch failed with error %d\n", err);
return JNI_FALSE;
}
}
return JNI_TRUE;
}
JNIEXPORT jlong JNICALL Java_FastGetField_accessFields(JNIEnv *env, jobject this, jobject obj) {
return
(*env)->GetBooleanField(env, obj, fieldIDs[0]) +
(*env)->GetByteField(env, obj, fieldIDs[1]) +
(*env)->GetCharField(env, obj, fieldIDs[2]) +
(*env)->GetShortField(env, obj, fieldIDs[3]) +
(*env)->GetIntField(env, obj, fieldIDs[4]) +
(*env)->GetLongField(env, obj, fieldIDs[5]) +
(jlong)((*env)->GetFloatField(env, obj, fieldIDs[6])) +
(jlong)((*env)->GetDoubleField(env, obj, fieldIDs[7]));
}
JNIEXPORT jlong JNICALL Java_FastGetField_getFieldAccessCount(JNIEnv *env, jclass c) {
return fieldAccessCount;
}
static void JNICALL onFieldAccess(jvmtiEnv *jvmti_env, JNIEnv* jni_env, jthread thread,
jmethodID method, jlocation location, jclass field_klass,
jobject object, jfieldID field) {
char *fname = NULL, *mname = NULL;
jvmtiError err = (*jvmti)->GetFieldName(jvmti, field_klass, field, &fname, NULL, NULL);
if (err != JVMTI_ERROR_NONE) {
printf("GetFieldName failed with error %d\n", err);
return;
}
err = (*jvmti)->GetMethodName(jvmti, method, &mname, NULL, NULL);
if (err != JVMTI_ERROR_NONE) {
printf("GetMethodName failed with error %d\n", err);
return;
}
printf("%s accessed field %s\n", mname, fname);
err = (*jvmti)->Deallocate(jvmti, (unsigned char*)fname);
if (err != JVMTI_ERROR_NONE) {
printf("Deallocate failed with error %d\n", err);
return;
}
err = (*jvmti)->Deallocate(jvmti, (unsigned char*)mname);
if (err != JVMTI_ERROR_NONE) {
printf("Deallocate failed with error %d\n", err);
return;
}
fieldAccessCount++;
}
JNIEXPORT jint JNICALL Agent_OnLoad(JavaVM* vm, char* options, void* reserved) {
jvmtiCapabilities capa;
jvmtiEventCallbacks cbs = {0};
(*vm)->GetEnv(vm, (void**)&jvmti, JVMTI_VERSION_1_0);
memset(&capa, 0, sizeof(capa));
capa.can_generate_field_access_events = 1;
(*jvmti)->AddCapabilities(jvmti, &capa);
cbs.FieldAccess = &onFieldAccess;
(*jvmti)->SetEventCallbacks(jvmti, &cbs, sizeof(cbs));
(*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE, JVMTI_EVENT_FIELD_ACCESS, NULL);
printf("Loaded agent\n");
fflush(stdout);
return 0;
}