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fix: avoid unsafe grouped int writes on aarch64+jdk8 #7834

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fix: avoid unsafe grouped int writes on aarch64+jdk8 #7834

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ac4d105
fix: bypass UNSAFE SWAR in readFieldNameHashCode on aarch64+JDK8 (#77…
yangpeng366 Aug 4, 2026
6d2eea3
fix: address wenshao review on #7755 - drop (byte) cast, gate os.arch…
yangpeng366 Aug 25, 2026
6b2f28d
fix: avoid unsafe grouped int writes on aarch64+jdk8
yangpeng366 Aug 27, 2026
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47 changes: 31 additions & 16 deletions core/src/main/java/com/alibaba/fastjson2/JSONReaderUTF16.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1115,6 +1115,11 @@ public final long readFieldNameHashCodeUnquote() {

@Override
public final long readFieldNameHashCode() {
// JDK 8 HotSpot C2 on aarch64 can miscompile the UNSAFE.getLong SWAR scan.
if (AARCH64_JDK8) {
return readFieldNameHashCode0();
}

final char[] chars = this.chars;
int ch = this.ch;
if (ch == '/') {
Expand Down Expand Up @@ -1181,6 +1186,11 @@ public final long readFieldNameHashCode() {

@Override
public final long readFieldNameHashCode(int keySize, int min, int max) {
// JDK 8 HotSpot C2 on aarch64 can miscompile the UNSAFE.getLong SWAR scan.
if (AARCH64_JDK8) {
return readFieldNameHashCode0();
}

final char[] chars = this.chars;
int ch = this.ch;
if (ch == '/') {
Expand Down Expand Up @@ -1252,6 +1262,11 @@ public final long readFieldNameHashCode(int keySize, int min, int max) {

@Override
public long readFieldNameHashCodeE(int size0, int size1, int size3) {
// JDK 8 HotSpot C2 on aarch64 can miscompile the UNSAFE.getLong SWAR scan.
if (AARCH64_JDK8) {
return readFieldNameHashCode0();
}

final char[] chars = this.chars;
int ch = this.ch;
if (ch == '/') {
Expand Down Expand Up @@ -1370,15 +1385,15 @@ private final long readFieldNameHashCode0() {
if (c0 == quote) {
nameValue = 0;
} else if (c1 == quote && c0 != 0 && c0 != '\\' && c0 <= 0xFF) {
nameValue = (byte) c0;
nameValue = c0;
this.nameLength = 1;
this.nameEnd = offset + 1;
offset += 2;
} else if (c2 == quote && c0 != 0
&& c0 != '\\' && c1 != '\\'
&& c0 <= 0xFF && c1 <= 0xFF
) {
nameValue = (((byte) c1) << 8)
nameValue = (c1 << 8)
+ c0;
this.nameLength = 2;
this.nameEnd = offset + 2;
Expand All @@ -1387,7 +1402,7 @@ private final long readFieldNameHashCode0() {
&& c0 != '\\' && c1 != '\\' && c2 != '\\'
&& c0 <= 0xFF && c1 <= 0xFF && c2 <= 0xFF) {
nameValue
= (((byte) c2) << 16)
= (c2 << 16)
+ (c1 << 8)
+ c0;
this.nameLength = 3;
Expand All @@ -1398,7 +1413,7 @@ private final long readFieldNameHashCode0() {
&& c0 <= 0xFF && c1 <= 0xFF && c2 <= 0xFF && c3 <= 0xFF
) {
nameValue
= (((byte) c3) << 24)
= (((long) c3) << 24)
+ (c2 << 16)
+ (c1 << 8)
+ c0;
Expand All @@ -1410,7 +1425,7 @@ private final long readFieldNameHashCode0() {
&& c0 <= 0xFF && c1 <= 0xFF && c2 <= 0xFF && c3 <= 0xFF && c4 <= 0xFF
) {
nameValue
= (((long) ((byte) c4)) << 32)
= (((long) c4) << 32)
+ (((long) c3) << 24)
+ (((long) c2) << 16)
+ (((long) c1) << 8)
Expand All @@ -1423,7 +1438,7 @@ private final long readFieldNameHashCode0() {
&& c0 <= 0xFF && c1 <= 0xFF && c2 <= 0xFF && c3 <= 0xFF && c4 <= 0xFF && c5 <= 0xFF
) {
nameValue
= (((long) ((byte) c5)) << 40)
= (((long) c5) << 40)
+ (((long) c4) << 32)
+ (((long) c3) << 24)
+ (((long) c2) << 16)
Expand All @@ -1437,7 +1452,7 @@ private final long readFieldNameHashCode0() {
&& c0 <= 0xFF && c1 <= 0xFF && c2 <= 0xFF && c3 <= 0xFF && c4 <= 0xFF && c5 <= 0xFF && c6 <= 0xFF
) {
nameValue
= (((long) ((byte) c6)) << 48)
= (((long) c6) << 48)
+ (((long) c5) << 40)
+ (((long) c4) << 32)
+ (((long) c3) << 24)
Expand All @@ -1452,7 +1467,7 @@ private final long readFieldNameHashCode0() {
&& c0 <= 0xFF && c1 <= 0xFF && c2 <= 0xFF && c3 <= 0xFF && c4 <= 0xFF && c5 <= 0xFF && c6 <= 0xFF && c7 <= 0xFF
) {
nameValue
= (((long) ((byte) c7)) << 56)
= (((long) c7) << 56)
+ (((long) c6) << 48)
+ (((long) c5) << 40)
+ (((long) c4) << 32)
Expand Down Expand Up @@ -1512,28 +1527,28 @@ private final long readFieldNameHashCode0() {

switch (i) {
case 0:
nameValue = (byte) c;
nameValue = c;
break;
case 1:
nameValue = (((byte) c) << 8) + (nameValue & 0xFFL);
nameValue = ((long) c << 8) + (nameValue & 0xFFL);
break;
case 2:
nameValue = (((byte) c) << 16) + (nameValue & 0xFFFFL);
nameValue = ((long) c << 16) + (nameValue & 0xFFFFL);
break;
case 3:
nameValue = (((byte) c) << 24) + (nameValue & 0xFFFFFFL);
nameValue = ((long) c << 24) + (nameValue & 0xFFFFFFL);
break;
case 4:
nameValue = (((long) (byte) c) << 32) + (nameValue & 0xFFFFFFFFL);
nameValue = ((long) c << 32) + (nameValue & 0xFFFFFFFFL);
break;
case 5:
nameValue = (((long) (byte) c) << 40L) + (nameValue & 0xFFFFFFFFFFL);
nameValue = ((long) c << 40L) + (nameValue & 0xFFFFFFFFFFL);
break;
case 6:
nameValue = (((long) (byte) c) << 48L) + (nameValue & 0xFFFFFFFFFFFFL);
nameValue = ((long) c << 48L) + (nameValue & 0xFFFFFFFFFFFFL);
break;
case 7:
nameValue = (((long) (byte) c) << 56L) + (nameValue & 0xFFFFFFFFFFFFFFL);
nameValue = ((long) c << 56L) + (nameValue & 0xFFFFFFFFFFFFFFL);
break;
default:
break;
Expand Down
62 changes: 62 additions & 0 deletions core/src/main/java/com/alibaba/fastjson2/util/IOUtils.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1200,6 +1200,9 @@ public static int writeLocalTime(char[] buf, int off, LocalTime time) {
}

private static int writeInt4(byte[] buf, int off, int v) {
if (JDKUtils.AARCH64_JDK8) {
return writeIntNSafe(buf, off, v, 4);
}
int v1 = (int) (v * 1374389535L >> 37); // v / 100;
int v0 = v - v1 * 100;
int v2 = PACKED_DIGITS[v1 & 0x7f] | (PACKED_DIGITS[v0 & 0x7f] << 16);
Expand All @@ -1211,6 +1214,9 @@ private static int writeInt4(byte[] buf, int off, int v) {
}

private static int writeInt4(char[] buf, int off, int v) {
if (JDKUtils.AARCH64_JDK8) {
return writeIntNSafe(buf, off, v, 4);
}
int v1 = (int) (v * 1374389535L >> 37); // v / 100;
putLongUnaligned(buf, off, mergeInt64(v - v1 * 100, v1));
return off + 4;
Expand All @@ -1225,18 +1231,27 @@ private static long mergeInt64(int v1, int v2) {
}

private static int writeInt3(byte[] buf, int off, int val) {
if (JDKUtils.AARCH64_JDK8) {
return writeInt3Safe(buf, off, val);
}
int v = DIGITS_K_32[val & 0x3ff];
UNSAFE.putInt(buf, ARRAY_BYTE_BASE_OFFSET + off, v >> ((((byte) v) + 1) << 3));
return off + 3 - (byte) v;
}

private static int writeInt3(char[] buf, int off, int val) {
if (JDKUtils.AARCH64_JDK8) {
return writeInt3Safe(buf, off, val);
}
long v = DIGITS_K_64[val & 0x3ff];
UNSAFE.putLong(buf, ARRAY_CHAR_BASE_OFFSET + ((long) off << 1), v >> ((((short) v) + 1) << 4));
return off + 3 - (byte) v;
}

private static int writeInt8(byte[] buf, int off, int v1, int v2) {
if (JDKUtils.AARCH64_JDK8) {
return writeInt8Safe(buf, off, v1, v2);
}
int r1 = (int) (v1 * 1374389535L >> 37); // v1 / 100;
int r2 = (int) (v2 * 1374389535L >> 37); // v2 / 100;
long v = (PACKED_DIGITS[r1 & 0x7f])
Expand All @@ -1251,6 +1266,9 @@ private static int writeInt8(byte[] buf, int off, int v1, int v2) {
}

private static int writeInt8(char[] buf, int off, int v1, int v2) {
if (JDKUtils.AARCH64_JDK8) {
return writeInt8Safe(buf, off, v1, v2);
}
int r1 = (int) (v1 * 1374389535L >> 37); // v1 / 100;
long x1 = (PACKED_DIGITS_UTF16[r1 & 0x7f])
| ((long) PACKED_DIGITS_UTF16[(v1 - r1 * 100) & 0x7f] << 32);
Expand All @@ -1266,6 +1284,50 @@ private static int writeInt8(char[] buf, int off, int v1, int v2) {
return off + 8;
}

static int writeInt3Safe(byte[] buf, int off, int value) {
int length = value < 100 ? (value < 10 ? 1 : 2) : 3;
for (int i = length; i > 0; i--) {
buf[off + i - 1] = (byte) ('0' + value % 10);
value /= 10;
}
return off + length;
}

static int writeInt3Safe(char[] buf, int off, int value) {
int length = value < 100 ? (value < 10 ? 1 : 2) : 3;
for (int i = length; i > 0; i--) {
buf[off + i - 1] = (char) ('0' + value % 10);
value /= 10;
}
return off + length;
}

static int writeIntNSafe(byte[] buf, int off, int value, int digits) {
for (int i = digits; i > 0; i--) {
buf[off + i - 1] = (byte) ('0' + value % 10);
value /= 10;
}
return off + digits;
}

static int writeIntNSafe(char[] buf, int off, int value, int digits) {
for (int i = digits; i > 0; i--) {
buf[off + i - 1] = (char) ('0' + value % 10);
value /= 10;
}
return off + digits;
}

static int writeInt8Safe(byte[] buf, int off, int high, int low) {
off = writeIntNSafe(buf, off, high, 4);
return writeIntNSafe(buf, off, low, 4);
}

static int writeInt8Safe(char[] buf, int off, int high, int low) {
off = writeIntNSafe(buf, off, high, 4);
return writeIntNSafe(buf, off, low, 4);
}

/**
* Writes a 64-bit long integer value to a byte array.
* This method converts a long integer to its string representation and writes it
Expand Down
12 changes: 12 additions & 0 deletions core/src/main/java/com/alibaba/fastjson2/util/JDKUtils.java
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Original file line number Diff line number Diff line change
Expand Up @@ -21,8 +21,11 @@ public class JDKUtils {
public static final long ARRAY_CHAR_BASE_OFFSET;

public static final int JVM_VERSION;
public static final String OS_ARCH;
public static final Byte LATIN1 = 0;
public static final boolean AARCH64;
public static final Byte UTF16 = 1;
public static final boolean AARCH64_JDK8;

public static final Field FIELD_STRING_VALUE;
public static final long FIELD_STRING_VALUE_OFFSET;
Expand Down Expand Up @@ -87,8 +90,10 @@ public class JDKUtils {
}

int jvmVersion = -1, android_sdk_int = -1;
String osArch = null;
boolean openj9 = false, android = false, graal = false;
try {
osArch = System.getProperty("os.arch");
String jvmName = System.getProperty("java.vm.name");
if (jvmName != null) {
openj9 = jvmName.contains("OpenJ9");
Expand Down Expand Up @@ -122,6 +127,9 @@ public class JDKUtils {
GRAAL = graal;
ANDROID_SDK_INT = android_sdk_int;

OS_ARCH = osArch;
AARCH64 = "aarch64".equals(osArch) || "arm64".equals(osArch);

boolean hasJavaSql = true;
Class dataSourceClass = null;
Class rowSetClass = null;
Expand All @@ -145,6 +153,10 @@ public class JDKUtils {
CLASS_TRANSIENT = transientClass;

JVM_VERSION = jvmVersion;
// JDK 8 HotSpot C2 on aarch64 can miscompile the UNSAFE.getLong SWAR
// field-name scan. Keep the safe char[] path for #7732/#3763 until
// affected JDK 8 builds are no longer supported.
AARCH64_JDK8 = AARCH64 && JVM_VERSION == 8 && !ANDROID && !GRAAL && !OPENJ9;

if (JVM_VERSION == 8) {
Field field = null;
Expand Down
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