#!/bin/bash
: <<'````````bash'
# Programming Exercise 7: Dynamic Binary Translation

Write a dynamic binary translator for RISC-V programs, in particular rv32i. To keep things simple, you only need to do the actual translation part and you can use a decoder library and LLVM for code generation.

## Implementation

Decode and lift RISC-V code with at least basic block granularity to LLVM-IR and use LLVM's JIT compiler. Emulate guest memory by reserving 4 GiB of virtual memory (`mmap(NULL, 0x100000000, PROT_NONE, MAP_PRIVATE|MAP_ANON|MAP_NORESERVE, -1, 0)`) and load the guest program at a command-line configurable address inside this virtual memory (use `mprotect(address, size, PROT_READ|PROT_WRITE)`, write the code there, and call mprotect again to change the code to read-only); use the base of the memory region as base for all guest memory accesses. Initialize a sufficiently large stack (again, use mprotect) and set the stack pointer to point at the top end. At the end of the program, dump the register state in human-readable form. Add a command-line option for single-stepping, where instead of basic blocks single instructions are translated, and for dumping the register state and program counter before entering a translated chunk.

You don't need to handle any ISA extensions, system calls, or modifyable code (although you are encouraged to implement some system calls for memory management and I/O). For decoding, you can use frvdec (https://git.sr.ht/~aengelke/frvdec/tree) or LLVM-MC. You may use the template below as starting point.


## Command Line Interface

    usage: ./bt (-s) program_file [program_args...]
        RISC-V user-space binary translator.
        -s: single-stepping mode.
        program_file: statically linked rv32i ELF executable.


## Analysis

Write (and submit) some sample programs to test the functionality of your emulator. Do some profiling to determine the performance-limiting factors. What could you do to improve the performance of your binary translator?


## Submission

- Submission deadline: 2025-01-22 23:59
- Submit using `curl --data-binary "@<your-submission-file>" 'https://db.in.tum.de/teaching/ws2425/codegen/submit.py?hw=7&matrno=<your-matrno>'`
- Write your solution in a single C++ file. (Default file name: `bt.cc`)
- Include answers to theory questions as comments at the top of the source file.
- Avoid dependencies, no build systems other than Makefile, etc.
- If you use frvdec, please copy header and source file into your submission
- If you need more than just the C++ file, combine all files s.t. this command sequence works: `split-file <submission> somedir; cd somedir; bash <hw7.txt>`
- If you write your own Makefile:
    - Use `$(LLVM_CONFIG) --cppflags --ldflags --libs` to find LLVM; note that libs must come after your object files when linking.
    - Default-initialize `LLVM_CONFIG := llvm-config`, so that `make LLVM_CONFIG=/path/to/llvm-config` overrides it.

There is no test script or automatic verification.

## Appendix: Template

    #include <err.h>
    #include <memory>
    #include <string>

    #include <llvm/ExecutionEngine/ExecutionEngine.h>
    #include <llvm/IR/LLVMContext.h>
    #include <llvm/IR/Module.h>
    #include <llvm/IR/IRBuilder.h>
    #include <llvm/Support/TargetSelect.h>

    using ChunkFunc = uint32_t(uint32_t* regs);

    // Compile function from module; module is consumed; returns nullptr on failure.
    void* compile(std::unique_ptr<llvm::Module> mod, const std::string& name) {
        std::string error;
        llvm::TargetOptions options;

        llvm::EngineBuilder builder(std::move(mod));
        builder.setEngineKind(llvm::EngineKind::JIT);
        builder.setErrorStr(&error);
        builder.setOptLevel(llvm::CodeGenOpt::None);
        builder.setTargetOptions(options);

        llvm::ExecutionEngine* engine = builder.create();
        if (!engine)
            err(1, "could not create engine: %s", error.c_str());
        return reinterpret_cast<void*>(engine->getFunctionAddress(name));
    }

    int main(int argc, char** argv) {
        llvm::InitializeNativeTarget();
        llvm::InitializeNativeTargetAsmPrinter();

        // Implement binary translator logic here.
        return 0;
    }

````````bash
set -euo pipefail

FAILED=0

CXX=g++ CXXFLAGS="-O3 -Wall -Wextra -std=c++20" make bt

exit $FAILED