wasmer/lib/llvm-backend/src/backend.rs

use crate::intrinsics::Intrinsics;
use inkwell::{
    memory_buffer::MemoryBuffer,
    module::Module,
    targets::{CodeModel, FileType, InitializationConfig, RelocMode, Target, TargetMachine},
    OptimizationLevel,
};
use libc::{
    c_char, mmap, mprotect, munmap, MAP_ANON, MAP_PRIVATE, PROT_EXEC, PROT_NONE, PROT_READ,
    PROT_WRITE,
};
use std::{
    ffi::CString,
    mem,
    ptr::{self, NonNull},
    slice, str,
};
use wasmer_runtime_core::{
    backend::{FuncResolver, ProtectedCaller, Token, UserTrapper},
    error::RuntimeResult,
    export::Context,
    module::{ModuleInfo, ModuleInner},
    structures::TypedIndex,
    types::{FuncIndex, FuncSig, LocalFuncIndex, LocalOrImport, SigIndex, Type, Value},
    vm::{self, ImportBacking},
    vmcalls,
};

#[repr(C)]
struct LLVMModule {
    _private: [u8; 0],
}

#[allow(non_camel_case_types, dead_code)]
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
#[repr(C)]
enum MemProtect {
    NONE,
    READ,
    READ_WRITE,
    READ_EXECUTE,
}

#[allow(non_camel_case_types, dead_code)]
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
#[repr(C)]
enum LLVMResult {
    OK,
    ALLOCATE_FAILURE,
    PROTECT_FAILURE,
    DEALLOC_FAILURE,
    OBJECT_LOAD_FAILURE,
}

#[repr(C)]
struct Callbacks {
    alloc_memory: extern "C" fn(usize, MemProtect, &mut *mut u8, &mut usize) -> LLVMResult,
    protect_memory: extern "C" fn(*mut u8, usize, MemProtect) -> LLVMResult,
    dealloc_memory: extern "C" fn(*mut u8, usize) -> LLVMResult,

    lookup_vm_symbol: extern "C" fn(*const c_char, usize) -> *const vm::Func,
}

extern "C" {
    fn module_load(
        mem_ptr: *const u8,
        mem_size: usize,
        callbacks: Callbacks,
        module_out: &mut *mut LLVMModule,
    ) -> LLVMResult;
    fn module_delete(module: *mut LLVMModule);
    fn get_func_symbol(module: *mut LLVMModule, name: *const c_char) -> *const vm::Func;
}

fn get_callbacks() -> Callbacks {
    fn round_up_to_page_size(size: usize) -> usize {
        (size + (4096 - 1)) & !(4096 - 1)
    }

    extern "C" fn alloc_memory(
        size: usize,
        protect: MemProtect,
        ptr_out: &mut *mut u8,
        size_out: &mut usize,
    ) -> LLVMResult {
        let size = round_up_to_page_size(size);
        let ptr = unsafe {
            mmap(
                ptr::null_mut(),
                size,
                match protect {
                    MemProtect::NONE => PROT_NONE,
                    MemProtect::READ => PROT_READ,
                    MemProtect::READ_WRITE => PROT_READ | PROT_WRITE,
                    MemProtect::READ_EXECUTE => PROT_READ | PROT_EXEC,
                },
                MAP_PRIVATE | MAP_ANON,
                -1,
                0,
            )
        };
        if ptr as isize == -1 {
            return LLVMResult::ALLOCATE_FAILURE;
        }
        *ptr_out = ptr as _;
        *size_out = size;
        LLVMResult::OK
    }

    extern "C" fn protect_memory(ptr: *mut u8, size: usize, protect: MemProtect) -> LLVMResult {
        let res = unsafe {
            mprotect(
                ptr as _,
                round_up_to_page_size(size),
                match protect {
                    MemProtect::NONE => PROT_NONE,
                    MemProtect::READ => PROT_READ,
                    MemProtect::READ_WRITE => PROT_READ | PROT_WRITE,
                    MemProtect::READ_EXECUTE => PROT_READ | PROT_EXEC,
                },
            )
        };

        if res == 0 {
            LLVMResult::OK
        } else {
            LLVMResult::PROTECT_FAILURE
        }
    }

    extern "C" fn dealloc_memory(ptr: *mut u8, size: usize) -> LLVMResult {
        let res = unsafe { munmap(ptr as _, round_up_to_page_size(size)) };

        if res == 0 {
            LLVMResult::OK
        } else {
            LLVMResult::DEALLOC_FAILURE
        }
    }

    extern "C" fn lookup_vm_symbol(name_ptr: *const c_char, length: usize) -> *const vm::Func {
        #[cfg(target_os = "macos")]
        macro_rules! fn_name {
            ($s:literal) => {
                concat!("_", $s)
            };
        }

        #[cfg(not(target_os = "macos"))]
        macro_rules! fn_name {
            ($s:literal) => {
                $s
            };
        }

        let name_slice = unsafe { slice::from_raw_parts(name_ptr as *const u8, length) };
        let name = str::from_utf8(name_slice).unwrap();

        match name {
            fn_name!("vm.memory.grow.dynamic.local") => vmcalls::local_dynamic_memory_grow as _,
            fn_name!("vm.memory.size.dynamic.local") => vmcalls::local_dynamic_memory_size as _,
            fn_name!("vm.memory.grow.static.local") => vmcalls::local_static_memory_grow as _,
            fn_name!("vm.memory.size.static.local") => vmcalls::local_static_memory_size as _,
            _ => ptr::null(),
        }
    }

    Callbacks {
        alloc_memory,
        protect_memory,
        dealloc_memory,
        lookup_vm_symbol,
    }
}

unsafe impl Send for LLVMBackend {}
unsafe impl Sync for LLVMBackend {}

pub struct LLVMBackend {
    module: *mut LLVMModule,
    #[allow(dead_code)]
    memory_buffer: MemoryBuffer,
}

impl LLVMBackend {
    pub fn new(module: Module, intrinsics: Intrinsics) -> (Self, LLVMProtectedCaller) {
        Target::initialize_x86(&InitializationConfig {
            asm_parser: true,
            asm_printer: true,
            base: true,
            disassembler: true,
            info: true,
            machine_code: true,
        });
        let triple = TargetMachine::get_default_triple().to_string();
        let target = Target::from_triple(&triple).unwrap();
        let target_machine = target
            .create_target_machine(
                &triple,
                &TargetMachine::get_host_cpu_name().to_string(),
                &TargetMachine::get_host_cpu_features().to_string(),
                OptimizationLevel::Default,
                RelocMode::PIC,
                CodeModel::Default,
            )
            .unwrap();

        let memory_buffer = target_machine
            .write_to_memory_buffer(&module, FileType::Object)
            .unwrap();
        let mem_buf_slice = memory_buffer.as_slice();

        let callbacks = get_callbacks();
        let mut module: *mut LLVMModule = ptr::null_mut();

        let res = unsafe {
            module_load(
                mem_buf_slice.as_ptr(),
                mem_buf_slice.len(),
                callbacks,
                &mut module,
            )
        };

        if res != LLVMResult::OK {
            panic!("failed to load object")
        }

        (
            Self {
                module,
                memory_buffer,
            },
            LLVMProtectedCaller { module },
        )
    }

    pub fn get_func(
        &self,
        info: &ModuleInfo,
        local_func_index: LocalFuncIndex,
    ) -> Option<NonNull<vm::Func>> {
        let index = local_func_index.index();
        let name = if cfg!(target_os = "macos") {
            format!("_fn{}", index)
        } else {
            format!("fn{}", index)
        };

        let c_str = CString::new(name).ok()?;
        let ptr = unsafe { get_func_symbol(self.module, c_str.as_ptr()) };

        NonNull::new(ptr as _)
    }
}

impl Drop for LLVMBackend {
    fn drop(&mut self) {
        unsafe { module_delete(self.module) }
    }
}

impl FuncResolver for LLVMBackend {
    fn get(
        &self,
        module: &ModuleInner,
        local_func_index: LocalFuncIndex,
    ) -> Option<NonNull<vm::Func>> {
        self.get_func(&module.info, local_func_index)
    }
}

struct Placeholder;

unsafe impl Send for LLVMProtectedCaller {}
unsafe impl Sync for LLVMProtectedCaller {}

pub struct LLVMProtectedCaller {
    module: *mut LLVMModule,
}

impl ProtectedCaller for LLVMProtectedCaller {
    fn call(
        &self,
        module: &ModuleInner,
        func_index: FuncIndex,
        params: &[Value],
        import_backing: &ImportBacking,
        vmctx: *mut vm::Ctx,
        _: Token,
    ) -> RuntimeResult<Vec<Value>> {
        let (func_ptr, ctx, signature, sig_index) =
            get_func_from_index(&module, import_backing, func_index);

        let vmctx_ptr = match ctx {
            Context::External(external_vmctx) => external_vmctx,
            Context::Internal => vmctx,
        };

        assert!(
            signature.returns().len() <= 1,
            "multi-value returns not yet supported"
        );

        assert!(
            signature.check_param_value_types(params),
            "incorrect signature"
        );

        let param_vec: Vec<u64> = params
            .iter()
            .map(|val| match val {
                Value::I32(x) => *x as u64,
                Value::I64(x) => *x as u64,
                Value::F32(x) => x.to_bits() as u64,
                Value::F64(x) => x.to_bits(),
            })
            .collect();

        let mut return_vec = vec![0; signature.returns().len()];

        let trampoline: unsafe extern "C" fn(*mut vm::Ctx, *const vm::Func, *const u64, *mut u64) = unsafe {
            let name = if cfg!(target_os = "macos") {
                format!("_trmp{}", sig_index.index())
            } else {
                format!("trmp{}", sig_index.index())
            };

            let c_str = CString::new(name).unwrap();
            let symbol = get_func_symbol(self.module, c_str.as_ptr());
            assert!(!symbol.is_null());

            mem::transmute(symbol)
        };

        // Here we go.
        unsafe {
            trampoline(
                vmctx_ptr,
                func_ptr,
                param_vec.as_ptr(),
                return_vec.as_mut_ptr(),
            );
        }

        Ok(return_vec
            .iter()
            .zip(signature.returns().iter())
            .map(|(&x, ty)| match ty {
                Type::I32 => Value::I32(x as i32),
                Type::I64 => Value::I64(x as i64),
                Type::F32 => Value::F32(f32::from_bits(x as u32)),
                Type::F64 => Value::F64(f64::from_bits(x as u64)),
            })
            .collect())
    }

    fn get_early_trapper(&self) -> Box<dyn UserTrapper> {
        Box::new(Placeholder)
    }
}

impl UserTrapper for Placeholder {
    unsafe fn do_early_trap(&self, msg: String) -> ! {
        unimplemented!("do early trap: {}", msg)
    }
}

fn get_func_from_index<'a>(
    module: &'a ModuleInner,
    import_backing: &ImportBacking,
    func_index: FuncIndex,
) -> (*const vm::Func, Context, &'a FuncSig, SigIndex) {
    let sig_index = *module
        .info
        .func_assoc
        .get(func_index)
        .expect("broken invariant, incorrect func index");

    let (func_ptr, ctx) = match func_index.local_or_import(&module.info) {
        LocalOrImport::Local(local_func_index) => (
            module
                .func_resolver
                .get(&module, local_func_index)
                .expect("broken invariant, func resolver not synced with module.exports")
                .cast()
                .as_ptr() as *const _,
            Context::Internal,
        ),
        LocalOrImport::Import(imported_func_index) => {
            let imported_func = import_backing.imported_func(imported_func_index);
            (
                imported_func.func as *const _,
                Context::External(imported_func.vmctx),
            )
        }
    };

    let signature = &module.info.signatures[sig_index];

    (func_ptr, ctx, signature, sig_index)
}

unsafe fn disass_ptr(ptr: *const u8, size: usize, inst_count: usize) {
    use capstone::arch::BuildsCapstone;
    let mut cs = capstone::Capstone::new() // Call builder-pattern
        .x86() // X86 architecture
        .mode(capstone::arch::x86::ArchMode::Mode64) // 64-bit mode
        .detail(true) // Generate extra instruction details
        .build()
        .expect("Failed to create Capstone object");

    // Get disassembled instructions
    let insns = cs
        .disasm_count(
            std::slice::from_raw_parts(ptr, size),
            ptr as u64,
            inst_count,
        )
        .expect("Failed to disassemble");

    println!("count = {}", insns.len());
    for insn in insns.iter() {
        println!(
            "0x{:x}: {:6} {}",
            insn.address(),
            insn.mnemonic().unwrap_or(""),
            insn.op_str().unwrap_or("")
        );
    }
}