Dynarmic

A dynamic recompiler for ARM.

Supported guest architectures

• ARMv6K
• 64-bit ARMv8

Supported host architectures

• x86-64

There are no plans to support x86-32.

Alternatives to Dynarmic

If you are looking at a recompiler which you can use with minimal effort to run ARM executables on non-native platforms, we would strongly recommend looking at qemu-user-static (description of qemu-user-static, using qemu-user-static in combination with Docker to provide a complete emulated environment). Having a complete plug-and-play solution is out-of-scope of this project.

Here are some projects with the same goals as dynarmic:

• ChocolArm64 from Ryujinx - ARMv8 recompiler on top of RyuJIT
• Unicorn - Recompiling multi-architecture CPU emulator, based on QEMU
• SkyEye - Cached interpreter for ARM

More general alternatives:

• tARMac - Tarmac's use of armlets was initial inspiration for us to use an intermediate representation
• QEMU - Recompiling multi-architecture system emulator
• VisUAL - Visual ARM UAL emulator intended for education
• A wide variety of other recompilers, interpreters and emulators can be found embedded in other projects, here are some we would recommend looking at:
  • firebird's recompiler - Takes more of a call-threaded approach to recompilation
  • higan's arm7tdmi emulator - Very clean code-style
  • arm-js by ozaki-r - Emulates ARMv7A and some peripherals of Versatile Express, in the browser

Disadvantages of Dynarmic

In the pursuit of speed, some behavior not commonly depended upon is elided. Therefore this emulator does not match spec.

Known examples:

• Only user-mode is emulated, there is no emulation of any other privilege levels.
• FPSR state is approximate.
• Misaligned loads/stores are not appropriately trapped in certain cases.
• Exclusive monitor behavior may not match any known physical processor.

As with most other hobby ARM emulation projects, no formal verification has been done. Use this code base at your own risk.

Documentation

Design documentation can be found at docs/Design.md.

Plans

Near-term

• Complete ARMv8 support

Medium-term

• Optimizations

Long-term

• ARMv7A guest support
• ARMv5 guest support
• ARMv8 host support

Usage Example

The below is a minimal example. Bring-your-own memory system.

#include <array>
#include <cstdint>
#include <cstdio>
#include <exception>

#include <dynarmic/A32/a32.h>
#include <dynarmic/A32/config.h>

using u8 = std::uint8_t;
using u16 = std::uint16_t;
using u32 = std::uint32_t;
using u64 = std::uint64_t;

class MyEnvironment final : public Dynarmic::A32::UserCallbacks {
public:
    u64 ticks_left = 0;
    std::array<u8, 2048> memory{};

    u8 MemoryRead8(u32 vaddr) override {
        if (vaddr >= memory.size()) {
            return 0;
        }
        return memory[vaddr];
    }

    u16 MemoryRead16(u32 vaddr) override {
        return u16(MemoryRead8(vaddr)) | u16(MemoryRead8(vaddr + 1)) << 8;
    }

    u32 MemoryRead32(u32 vaddr) override {
        return u32(MemoryRead16(vaddr)) | u32(MemoryRead16(vaddr + 2)) << 16;
    }

    u64 MemoryRead64(u32 vaddr) override {
        return u64(MemoryRead32(vaddr)) | u64(MemoryRead32(vaddr + 4)) << 32;
    }

    void MemoryWrite8(u32 vaddr, u8 value) override {
        if (vaddr >= memory.size()) {
            return;
        }
        memory[vaddr] = value;
    }

    void MemoryWrite16(u32 vaddr, u16 value) override {
        MemoryWrite8(vaddr, u8(value));
        MemoryWrite8(vaddr + 1, u8(value >> 8));
    }

    void MemoryWrite32(u32 vaddr, u32 value) override {
        MemoryWrite16(vaddr, u16(value));
        MemoryWrite16(vaddr + 2, u16(value >> 16));
    }

    void MemoryWrite64(u32 vaddr, u64 value) override {
        MemoryWrite32(vaddr, u32(value));
        MemoryWrite32(vaddr + 4, u32(value >> 32));
    }

    void InterpreterFallback(u32 pc, size_t num_instructions) override {
        // This is never called in practice.
        std::terminate();
    }

    void CallSVC(u32 swi) override {
        // Do something.
    }

    void ExceptionRaised(u32 pc, Dynarmic::A32::Exception exception) override {
        // Do something.
    }

    void AddTicks(u64 ticks) override {
        if (ticks > ticks_left) {
            ticks_left = 0;
            return;
        }
        ticks_left -= ticks;
    }

    u64 GetTicksRemaining() override {
        return ticks_left;
    }
};

int main(int argc, char** argv) {
    MyEnvironment env;
    Dynarmic::A32::UserConfig user_config;
    user_config.callbacks = &env;
    Dynarmic::A32::Jit cpu{user_config};

    // Execute at least 1 instruction.
    // (Note: More than one instruction may be executed.)
    env.ticks_left = 1;

    // Write some code to memory.
    env.MemoryWrite16(0, 0x0088); // lsls r0, r1, #2
    env.MemoryWrite16(2, 0xE7FE); // b +#0 (infinite loop)

    // Setup registers.
    cpu.Regs()[0] = 1;
    cpu.Regs()[1] = 2;
    cpu.Regs()[15] = 0; // PC = 0
    cpu.SetCpsr(0x00000030); // Thumb mode

    // Execute!
    cpu.Run();

    // Here we would expect cpu.Regs()[0] == 8
    printf("R0: %u\n", cpu.Regs()[0]);

    return 0;
}