ffmasm

ffmasm is an assembler for hand-assembling from Java.
It uses Foreign Function & Memory API, so the application can call assembled code via MethodHandle.

• Javadoc: https://yasuenag.github.io/ffmasm/
• Maven package: https://github.com/YaSuenag/ffmasm/packages/
• Supported instructions: See builder classes in com.yasuenag.ffmasm.amd64.

Requirements

Java 22

Supported platform

• Linux AMD64
• Windows AMD64
• Linux AArch64

How to build

$ mvn package

Test for ffmasm

$ mvn test

How to use

See Javadoc and cpumodel examples.

1. Create CodeSegment

CodeSegment is a storage for assembled code. In Linux, it would be allocated by mmap(2) with executable bit.
It implements AutoCloseable, so you can use try-with-resources in below:

try(var seg = new CodeSegment()){
  ...
}

2. Create MethodHandle

You can assemble the code via inner classes of com.yasuenag.ffmasm.AsmBuilder:

• AsmBuilder.AMD64
• AsmBuilder.SSE
• AsmBuilder.AVX
• AsmBuilder.AArch64

AMD64

You need to use com.yasuenag.ffmasm.amd64.Register to specify registers in assembly code. Following example shows how you can create method (I)I (JNI signature) in ffmasm:

You can get MethodHandle in result of build().

var desc = FunctionDescriptor.of(
             ValueLayout.JAVA_INT, // return value
             ValueLayout.JAVA_INT // 1st argument
           );

var method = new AsmBuilder.AMD64(seg, desc)
      /* push %rbp      */ .push(Register.RBP)
      /* mov %rsp, %rbp */ .movRM(Register.RSP, Register.RBP, OptionalInt.empty())
      /* mov %rdi, %rax */ .movRM(Register.RDI, Register.RAX, OptionalInt.empty())
      /* leave          */ .leave()
      /* ret            */ .ret()
                           .build(Linker.Option.critical(false));

Note

Linker.Option.critical() is recommended to pass build() method due to performance, but it might be cause of some issues in JVM (time to synchronize safepoint, memory corruption, etc). See Javadoc of critical().

AArch64

Most of code is same with AMD64, but it is the only one difference to use AsmBuilder.AArch64 as builder instance.

var desc = FunctionDescriptor.of(
             ValueLayout.JAVA_INT, // return value
             ValueLayout.JAVA_INT // 1st argument
           );

var method = new AsmBuilder.AArch64(codeSegment, desc)
/* stp x29, x30, [sp, #-16]! */ .stp(Register.X29, Register.X30, Register.SP, IndexClass.PreIndex, -16)
/* mov x29,  sp              */ .mov(Register.X29, Register.SP)
/* ldp x29, x30, [sp], #16   */ .ldp(Register.X29, Register.X30, Register.SP, IndexClass.PostIndex, 16)
/* ret                       */ .ret(Optional.empty())
                                .build();

3. Method call

int ret = (int)method.invoke(100); // "ret" should be 100

Debugging

ffmasm-disassembler can disassemble the code in MemorySegment like generated by ffmasm, and dump assembly code to stdout.

You can download ffmasm-dissassembler Maven package from GitHub packages: https://github.com/YaSuenag/ffmasm/packages/2370043

See examples/disas for details.

Requirements

ffmasm-disassembler requires hsdis.

Generate hsdis

To generate hsdis for Linux, you can use hsdis-builder.

Deploy hsdis

It should be deployed one of following directory (it is documented as source comment in disassembler.cpp in HotSpot):

1. $JAVA_HOME/lib/<vm>/libhsdis-<arch>.so
2. $JAVA_HOME/lib/<vm>/hsdis-<arch>.so
3. $JAVA_HOME/lib/hsdis-<arch>.so
4. hsdis-<arch>.so (using LD_LIBRARY_PATH)

If you don't want to deploy hsdis into your JDK, you can specify hsdis system property like -Dhsdis=/path/to/hsdis-amd64.so

Examples

import com.yasuenag.ffmasmtools.disas.Disassembler;

    : <snip>

MemorySegment rdtsc = createRDTSC(); // Generate machine code with ffmasm
Disassembler.dumpToStdout(rdtsc); // Dump assembly code of `rdtsc` to stdout

Play with JNI

You can bind native method to MemorySegment of ffmasm code dynamically.

You have to construct MemorySegment of the machine code with AMD64AsmBuilder, and you have to get it from getMemorySegment(). Then you can bind it via NativeRegister.

Following example shows native method test is binded to the code made by ffmasm. Note that 1st argument in Java is located at arg3 in native function because this is native function (1st arg is JNIEnv*, and 2nd arg is jobject or jclass).

public native int test(int arg);

<snip>

try(var seg = new CodeSegment()){
  var desc = FunctionDescriptor.of(
               ValueLayout.JAVA_INT, // return value
               ValueLayout.JAVA_INT, // 1st arg (JNIEnv *)
               ValueLayout.JAVA_INT, // 2nd arg (jobject)
               ValueLayout.JAVA_INT  // 3rd arg (arg1 of caller)
             );
  var stub = AsmBuilder.AMD64(seg, desc)
/* push %rbp         */ .push(Register.RBP)
/* mov %rsp, %rbp    */ .movRM(Register.RBP, Register.RSP, OptionalInt.empty())
/* mov %arg3, retReg */ .movMR(argReg.arg3(), argReg.returnReg(), OptionalInt.empty()) // arg1 in Java is arg3 in native
/* leave             */ .leave()
/* ret               */ .ret()
                        .getMemorySegment();

  var method = this.getClass()
                   .getMethod("test", int.class);

  var methodMap = Map.of(method, stub);
  var register = NativeRegister.create(this.getClass());
  register.registerNatives(methodMap);

  final int expected = 100;
  int actual = test(expected);
  Assertions.assertEquals(expected, actual);
}

Play with perf tool

You can record both function name and entry point address as a perf map file.

Record function

You can pass function name into build() method:

.build("GeneratedFunc", Linker.Option.critical(true));

Function name would be set to <unnamed> if you do not pass function name (includes calling build(Linker.Option)).

Write to map file

perf map file would be written at shutdown hook when CodeSegment lives. All of functions in all of CodeSegments which are lives would be dumped at the time of shutdown hook.

You need to enable perf map dumper via CodeSegment::enablePerfMapDumper. Call CodeSegment::disablePerfMapDumper if you want to cancel the dumper.

Generate jitdump

perf tool on Linux supports JIT-generated code. ffmasm can dump generated code as a jitdump. See an example for details.

Record assembled code as a JIT'ed code

Pass JitDump insntace to build method.

jitdump = JitDump.getInstance(Path.of("."));

    :

.build("GeneratedFunc", jitdump);

Then you can run perf record. Note that you have to set monotonic clock with -k option.

perf record -k 1 $JAVA_HOME/bin/java ...

As a result, you would get jit-<PID>.dump which includes JIT information. You should keep until run perf inject.

Inject JIT'ed code into recording file

perf.data generated by perf record would not include JIT'ed code, so you need to inject them via perf inject as following.

perf inject --jit -i perf.data -o perf.jit.data

You will get some .so file and perf.jit.data as an injected file as a result.

Check with perf report

perf report -i perf.jit.data

License

The GNU Lesser General Public License, version 3.0