Commit 24a01eed90

Andrew Kelley <andrew@ziglang.org>
2020-04-23 22:41:20
basics of writing ELF and machine code generation
1 parent a3dfe36
Changed files (4)
src-self-hosted/codegen.zig
@@ -1,447 +1,137 @@
 const std = @import("std");
-const Compilation = @import("compilation.zig").Compilation;
-const llvm = @import("llvm.zig");
-const c = @import("c.zig");
+const mem = std.mem;
+const assert = std.debug.assert;
 const ir = @import("ir.zig");
-const Value = @import("value.zig").Value;
 const Type = @import("type.zig").Type;
-const Scope = @import("scope.zig").Scope;
-const util = @import("util.zig");
-const event = std.event;
-const assert = std.debug.assert;
-const DW = std.dwarf;
-const maxInt = std.math.maxInt;
-
-pub async fn renderToLlvm(comp: *Compilation, fn_val: *Value.Fn, code: *ir.Code) Compilation.BuildError!void {
-    fn_val.base.ref();
-    defer fn_val.base.deref(comp);
-    defer code.destroy(comp.gpa());
-
-    var output_path = try comp.createRandomOutputPath(comp.target.oFileExt());
-    errdefer output_path.deinit();
-
-    const llvm_handle = try comp.zig_compiler.getAnyLlvmContext();
-    defer llvm_handle.release(comp.zig_compiler);
-
-    const context = llvm_handle.node.data;
-
-    const module = llvm.ModuleCreateWithNameInContext(comp.name.span(), context) orelse return error.OutOfMemory;
-    defer llvm.DisposeModule(module);
-
-    llvm.SetTarget(module, comp.llvm_triple.span());
-    llvm.SetDataLayout(module, comp.target_layout_str);
-
-    if (comp.target.getObjectFormat() == .coff) {
-        llvm.AddModuleCodeViewFlag(module);
-    } else {
-        llvm.AddModuleDebugInfoFlag(module);
-    }
-
-    const builder = llvm.CreateBuilderInContext(context) orelse return error.OutOfMemory;
-    defer llvm.DisposeBuilder(builder);
-
-    const dibuilder = llvm.CreateDIBuilder(module, true) orelse return error.OutOfMemory;
-    defer llvm.DisposeDIBuilder(dibuilder);
-
-    // Don't use ZIG_VERSION_STRING here. LLVM misparses it when it includes
-    // the git revision.
-    const producer = try std.fmt.allocPrintZ(&code.arena.allocator, "zig {}.{}.{}", .{
-        @as(u32, c.ZIG_VERSION_MAJOR),
-        @as(u32, c.ZIG_VERSION_MINOR),
-        @as(u32, c.ZIG_VERSION_PATCH),
-    });
-    const flags = "";
-    const runtime_version = 0;
-    const compile_unit_file = llvm.CreateFile(
-        dibuilder,
-        comp.name.span(),
-        comp.root_package.root_src_dir.span(),
-    ) orelse return error.OutOfMemory;
-    const is_optimized = comp.build_mode != .Debug;
-    const compile_unit = llvm.CreateCompileUnit(
-        dibuilder,
-        DW.LANG_C99,
-        compile_unit_file,
-        producer,
-        is_optimized,
-        flags,
-        runtime_version,
-        "",
-        0,
-        !comp.strip,
-    ) orelse return error.OutOfMemory;
-
-    var ofile = ObjectFile{
-        .comp = comp,
-        .module = module,
-        .builder = builder,
-        .dibuilder = dibuilder,
-        .context = context,
-        .lock = event.Lock.init(),
-        .arena = &code.arena.allocator,
-    };
-
-    try renderToLlvmModule(&ofile, fn_val, code);
-
-    // TODO module level assembly
-    //if (buf_len(&g->global_asm) != 0) {
-    //    LLVMSetModuleInlineAsm(g->module, buf_ptr(&g->global_asm));
-    //}
-
-    llvm.DIBuilderFinalize(dibuilder);
-
-    if (comp.verbose_llvm_ir) {
-        std.debug.warn("raw module:\n", .{});
-        llvm.DumpModule(ofile.module);
-    }
+const Value = @import("value.zig").Value;
 
-    // verify the llvm module when safety is on
-    if (std.debug.runtime_safety) {
-        var error_ptr: ?[*:0]u8 = null;
-        _ = llvm.VerifyModule(ofile.module, llvm.AbortProcessAction, &error_ptr);
-    }
+pub const ErrorMsg = struct {
+    byte_offset: usize,
+    msg: []const u8,
+};
 
-    const is_small = comp.build_mode == .ReleaseSmall;
-    const is_debug = comp.build_mode == .Debug;
+pub const Symbol = struct {
+    errors: []ErrorMsg,
 
-    var err_msg: [*:0]u8 = undefined;
-    // TODO integrate this with evented I/O
-    if (llvm.TargetMachineEmitToFile(
-        comp.target_machine,
-        module,
-        output_path.span(),
-        llvm.EmitBinary,
-        &err_msg,
-        is_debug,
-        is_small,
-    )) {
-        if (std.debug.runtime_safety) {
-            std.debug.panic("unable to write object file {}: {s}\n", .{ output_path.span(), err_msg });
+    pub fn deinit(self: *Symbol, allocator: *mem.Allocator) void {
+        for (self.errors) |err| {
+            allocator.free(err.msg);
         }
-        return error.WritingObjectFileFailed;
-    }
-    //validate_inline_fns(g); TODO
-    fn_val.containing_object = output_path;
-    if (comp.verbose_llvm_ir) {
-        std.debug.warn("optimized module:\n", .{});
-        llvm.DumpModule(ofile.module);
-    }
-    if (comp.verbose_link) {
-        std.debug.warn("created {}\n", .{output_path.span()});
-    }
-}
-
-pub const ObjectFile = struct {
-    comp: *Compilation,
-    module: *llvm.Module,
-    builder: *llvm.Builder,
-    dibuilder: *llvm.DIBuilder,
-    context: *llvm.Context,
-    lock: event.Lock,
-    arena: *std.mem.Allocator,
-
-    fn gpa(self: *ObjectFile) *std.mem.Allocator {
-        return self.comp.gpa();
+        allocator.free(self.errors);
+        self.* = undefined;
     }
 };
 
-pub fn renderToLlvmModule(ofile: *ObjectFile, fn_val: *Value.Fn, code: *ir.Code) !void {
-    // TODO audit more of codegen.cpp:fn_llvm_value and port more logic
-    const llvm_fn_type = try fn_val.base.typ.getLlvmType(ofile.arena, ofile.context);
-    const llvm_fn = llvm.AddFunction(
-        ofile.module,
-        fn_val.symbol_name.span(),
-        llvm_fn_type,
-    ) orelse return error.OutOfMemory;
-
-    const want_fn_safety = fn_val.block_scope.?.safety.get(ofile.comp);
-    if (want_fn_safety and ofile.comp.haveLibC()) {
-        try addLLVMFnAttr(ofile, llvm_fn, "sspstrong");
-        try addLLVMFnAttrStr(ofile, llvm_fn, "stack-protector-buffer-size", "4");
+pub fn generateSymbol(typed_value: ir.TypedValue, module: ir.Module, code: *std.ArrayList(u8)) !Symbol {
+    switch (typed_value.ty.zigTypeTag()) {
+        .Fn => {
+            const index = typed_value.val.cast(Value.Payload.Function).?.index;
+            const module_fn = module.fns[index];
+
+            var function = Function{
+                .module = &module,
+                .mod_fn = &module_fn,
+                .code = code,
+                .inst_table = std.AutoHashMap(*ir.Inst, Function.MCValue).init(code.allocator),
+                .errors = std.ArrayList(ErrorMsg).init(code.allocator),
+                .constants = std.ArrayList(ir.TypedValue).init(code.allocator),
+            };
+            defer function.inst_table.deinit();
+            defer function.errors.deinit();
+
+            for (module_fn.body) |inst| {
+                const new_inst = function.genFuncInst(inst) catch |err| switch (err) {
+                    error.CodegenFail => {
+                        assert(function.errors.items.len != 0);
+                        break;
+                    },
+                    else => |e| return e,
+                };
+                try function.inst_table.putNoClobber(inst, new_inst);
+            }
+            return Symbol{ .errors = function.errors.toOwnedSlice() };
+        },
+        else => @panic("TODO implement generateSymbol for non-function types"),
     }
+}
 
-    // TODO
-    //if (fn_val.align_stack) |align_stack| {
-    //    try addLLVMFnAttrInt(ofile, llvm_fn, "alignstack", align_stack);
-    //}
-
-    const fn_type = fn_val.base.typ.cast(Type.Fn).?;
-    const fn_type_normal = &fn_type.key.data.Normal;
-
-    try addLLVMFnAttr(ofile, llvm_fn, "nounwind");
-    //add_uwtable_attr(g, fn_table_entry->llvm_value);
-    try addLLVMFnAttr(ofile, llvm_fn, "nobuiltin");
-
-    //if (g->build_mode == BuildModeDebug && fn_table_entry->fn_inline != FnInlineAlways) {
-    //    ZigLLVMAddFunctionAttr(fn_table_entry->llvm_value, "no-frame-pointer-elim", "true");
-    //    ZigLLVMAddFunctionAttr(fn_table_entry->llvm_value, "no-frame-pointer-elim-non-leaf", nullptr);
-    //}
-
-    //if (fn_table_entry->section_name) {
-    //    LLVMSetSection(fn_table_entry->llvm_value, buf_ptr(fn_table_entry->section_name));
-    //}
-    //if (fn_table_entry->align_bytes > 0) {
-    //    LLVMSetAlignment(fn_table_entry->llvm_value, (unsigned)fn_table_entry->align_bytes);
-    //} else {
-    //    // We'd like to set the best alignment for the function here, but on Darwin LLVM gives
-    //    // "Cannot getTypeInfo() on a type that is unsized!" assertion failure when calling
-    //    // any of the functions for getting alignment. Not specifying the alignment should
-    //    // use the ABI alignment, which is fine.
-    //}
-
-    //if (!type_has_bits(return_type)) {
-    //    // nothing to do
-    //} else if (type_is_codegen_pointer(return_type)) {
-    //    addLLVMAttr(fn_table_entry->llvm_value, 0, "nonnull");
-    //} else if (handle_is_ptr(return_type) &&
-    //        calling_convention_does_first_arg_return(fn_type->data.fn.fn_type_id.cc))
-    //{
-    //    addLLVMArgAttr(fn_table_entry->llvm_value, 0, "sret");
-    //    addLLVMArgAttr(fn_table_entry->llvm_value, 0, "nonnull");
-    //}
-
-    // TODO set parameter attributes
-
-    // TODO
-    //uint32_t err_ret_trace_arg_index = get_err_ret_trace_arg_index(g, fn_table_entry);
-    //if (err_ret_trace_arg_index != UINT32_MAX) {
-    //    addLLVMArgAttr(fn_table_entry->llvm_value, (unsigned)err_ret_trace_arg_index, "nonnull");
-    //}
-
-    const cur_ret_ptr = if (fn_type_normal.return_type.handleIsPtr()) llvm.GetParam(llvm_fn, 0) else null;
-
-    // build all basic blocks
-    for (code.basic_block_list.span()) |bb| {
-        bb.llvm_block = llvm.AppendBasicBlockInContext(
-            ofile.context,
-            llvm_fn,
-            bb.name_hint,
-        ) orelse return error.OutOfMemory;
-    }
-    const entry_bb = code.basic_block_list.at(0);
-    llvm.PositionBuilderAtEnd(ofile.builder, entry_bb.llvm_block);
-
-    llvm.ClearCurrentDebugLocation(ofile.builder);
-
-    // TODO set up error return tracing
-    // TODO allocate temporary stack values
-
-    const var_list = fn_type.non_key.Normal.variable_list.span();
-    // create debug variable declarations for variables and allocate all local variables
-    for (var_list) |var_scope, i| {
-        const var_type = switch (var_scope.data) {
-            .Const => unreachable,
-            .Param => |param| param.typ,
-        };
-        //    if (!type_has_bits(var->value->type)) {
-        //        continue;
-        //    }
-        //    if (ir_get_var_is_comptime(var))
-        //        continue;
-        //    if (type_requires_comptime(var->value->type))
-        //        continue;
-        //    if (var->src_arg_index == SIZE_MAX) {
-        //        var->value_ref = build_alloca(g, var->value->type, buf_ptr(&var->name), var->align_bytes);
-
-        //        var->di_loc_var = ZigLLVMCreateAutoVariable(g->dbuilder, get_di_scope(g, var->parent_scope),
-        //                buf_ptr(&var->name), import->di_file, (unsigned)(var->decl_node->line + 1),
-        //                var->value->type->di_type, !g->strip_debug_symbols, 0);
-
-        //    } else {
-        // it's a parameter
-        //        assert(var->gen_arg_index != SIZE_MAX);
-        //        TypeTableEntry *gen_type;
-        //        FnGenParamInfo *gen_info = &fn_table_entry->type_entry->data.fn.gen_param_info[var->src_arg_index];
+const Function = struct {
+    module: *const ir.Module,
+    mod_fn: *const ir.Module.Fn,
+    code: *std.ArrayList(u8),
+    inst_table: std.AutoHashMap(*ir.Inst, MCValue),
+    /// Constants are embedded within functions (at the end, after `ret`)
+    /// so that they are independently updateable.
+    /// This is a list of constants that must be appended to the symbol after `ret`.
+    constants: std.ArrayList(ir.TypedValue),
+    errors: std.ArrayList(ErrorMsg),
+
+    const MCValue = union(enum) {
+        none,
+        unreach,
+        /// A pointer-sized integer that fits in a register.
+        immediate: u64,
+        /// Refers to the index into `constants` field of `Function`.
+        local_const_ptr: usize,
+    };
 
-        if (var_type.handleIsPtr()) {
-            //            if (gen_info->is_byval) {
-            //                gen_type = var->value->type;
-            //            } else {
-            //                gen_type = gen_info->type;
-            //            }
-            var_scope.data.Param.llvm_value = llvm.GetParam(llvm_fn, @intCast(c_uint, i));
-        } else {
-            //            gen_type = var->value->type;
-            var_scope.data.Param.llvm_value = try renderAlloca(ofile, var_type, var_scope.name, .Abi);
+    fn genFuncInst(self: *Function, inst: *ir.Inst) !MCValue {
+        switch (inst.tag) {
+            .unreach => return self.genPanic(inst.src),
+            .constant => unreachable, // excluded from function bodies
+            .assembly => return self.genAsm(inst.cast(ir.Inst.Assembly).?),
+            .ptrtoint => return self.genPtrToInt(inst.cast(ir.Inst.PtrToInt).?),
         }
-        //        if (var->decl_node) {
-        //            var->di_loc_var = ZigLLVMCreateParameterVariable(g->dbuilder, get_di_scope(g, var->parent_scope),
-        //                    buf_ptr(&var->name), import->di_file,
-        //                    (unsigned)(var->decl_node->line + 1),
-        //                    gen_type->di_type, !g->strip_debug_symbols, 0, (unsigned)(var->gen_arg_index + 1));
-        //        }
-
-        //    }
     }
 
-    // TODO finishing error return trace setup. we have to do this after all the allocas.
-
-    // create debug variable declarations for parameters
-    // rely on the first variables in the variable_list being parameters.
-    //size_t next_var_i = 0;
-    for (fn_type.key.data.Normal.params) |param, i| {
-        //FnGenParamInfo *info = &fn_table_entry->type_entry->data.fn.gen_param_info[param_i];
-        //if (info->gen_index == SIZE_MAX)
-        //    continue;
-        const scope_var = var_list[i];
-        //assert(variable->src_arg_index != SIZE_MAX);
-        //next_var_i += 1;
-        //assert(variable);
-        //assert(variable->value_ref);
-
-        if (!param.typ.handleIsPtr()) {
-            //clear_debug_source_node(g);
-            const llvm_param = llvm.GetParam(llvm_fn, @intCast(c_uint, i));
-            _ = try renderStoreUntyped(
-                ofile,
-                llvm_param,
-                scope_var.data.Param.llvm_value,
-                .Abi,
-                .Non,
-            );
+    fn genPanic(self: *Function, src: usize) !MCValue {
+        // TODO change this to call the panic function
+        switch (self.module.target.cpu.arch) {
+            .i386, .x86_64 => {
+                try self.code.append(0xcc); // x86 int3
+            },
+            else => return self.fail(src, "TODO implement panic for {}", .{self.module.target.cpu.arch}),
         }
-
-        //if (variable->decl_node) {
-        //    gen_var_debug_decl(g, variable);
-        //}
+        return .unreach;
     }
 
-    for (code.basic_block_list.span()) |current_block| {
-        llvm.PositionBuilderAtEnd(ofile.builder, current_block.llvm_block);
-        for (current_block.instruction_list.span()) |instruction| {
-            if (instruction.ref_count == 0 and !instruction.hasSideEffects()) continue;
-
-            instruction.llvm_value = try instruction.render(ofile, fn_val);
-        }
-        current_block.llvm_exit_block = llvm.GetInsertBlock(ofile.builder);
+    fn genAsm(self: *Function, inst: *ir.Inst.Assembly) !MCValue {
+        return self.fail(inst.base.src, "TODO machine code gen assembly", .{});
     }
-}
-
-fn addLLVMAttr(
-    ofile: *ObjectFile,
-    val: *llvm.Value,
-    attr_index: llvm.AttributeIndex,
-    attr_name: []const u8,
-) !void {
-    const kind_id = llvm.GetEnumAttributeKindForName(attr_name.ptr, attr_name.len);
-    assert(kind_id != 0);
-    const llvm_attr = llvm.CreateEnumAttribute(ofile.context, kind_id, 0) orelse return error.OutOfMemory;
-    llvm.AddAttributeAtIndex(val, attr_index, llvm_attr);
-}
-
-fn addLLVMAttrStr(
-    ofile: *ObjectFile,
-    val: *llvm.Value,
-    attr_index: llvm.AttributeIndex,
-    attr_name: []const u8,
-    attr_val: []const u8,
-) !void {
-    const llvm_attr = llvm.CreateStringAttribute(
-        ofile.context,
-        attr_name.ptr,
-        @intCast(c_uint, attr_name.len),
-        attr_val.ptr,
-        @intCast(c_uint, attr_val.len),
-    ) orelse return error.OutOfMemory;
-    llvm.AddAttributeAtIndex(val, attr_index, llvm_attr);
-}
-
-fn addLLVMAttrInt(
-    val: *llvm.Value,
-    attr_index: llvm.AttributeIndex,
-    attr_name: []const u8,
-    attr_val: u64,
-) !void {
-    const kind_id = llvm.GetEnumAttributeKindForName(attr_name.ptr, attr_name.len);
-    assert(kind_id != 0);
-    const llvm_attr = llvm.CreateEnumAttribute(ofile.context, kind_id, attr_val) orelse return error.OutOfMemory;
-    llvm.AddAttributeAtIndex(val, attr_index, llvm_attr);
-}
-
-fn addLLVMFnAttr(ofile: *ObjectFile, fn_val: *llvm.Value, attr_name: []const u8) !void {
-    return addLLVMAttr(ofile, fn_val, maxInt(llvm.AttributeIndex), attr_name);
-}
 
-fn addLLVMFnAttrStr(ofile: *ObjectFile, fn_val: *llvm.Value, attr_name: []const u8, attr_val: []const u8) !void {
-    return addLLVMAttrStr(ofile, fn_val, maxInt(llvm.AttributeIndex), attr_name, attr_val);
-}
-
-fn addLLVMFnAttrInt(ofile: *ObjectFile, fn_val: *llvm.Value, attr_name: []const u8, attr_val: u64) !void {
-    return addLLVMAttrInt(ofile, fn_val, maxInt(llvm.AttributeIndex), attr_name, attr_val);
-}
-
-fn renderLoadUntyped(
-    ofile: *ObjectFile,
-    ptr: *llvm.Value,
-    alignment: Type.Pointer.Align,
-    vol: Type.Pointer.Vol,
-    name: [*:0]const u8,
-) !*llvm.Value {
-    const result = llvm.BuildLoad(ofile.builder, ptr, name) orelse return error.OutOfMemory;
-    switch (vol) {
-        .Non => {},
-        .Volatile => llvm.SetVolatile(result, 1),
+    fn genPtrToInt(self: *Function, inst: *ir.Inst.PtrToInt) !MCValue {
+        // no-op
+        return self.resolveInst(inst.args.ptr);
     }
-    llvm.SetAlignment(result, resolveAlign(ofile, alignment, llvm.GetElementType(llvm.TypeOf(ptr))));
-    return result;
-}
 
-fn renderLoad(ofile: *ObjectFile, ptr: *llvm.Value, ptr_type: *Type.Pointer, name: [*:0]const u8) !*llvm.Value {
-    return renderLoadUntyped(ofile, ptr, ptr_type.key.alignment, ptr_type.key.vol, name);
-}
-
-pub fn getHandleValue(ofile: *ObjectFile, ptr: *llvm.Value, ptr_type: *Type.Pointer) !?*llvm.Value {
-    const child_type = ptr_type.key.child_type;
-    if (!child_type.hasBits()) {
-        return null;
-    }
-    if (child_type.handleIsPtr()) {
-        return ptr;
+    fn resolveInst(self: *Function, inst: *ir.Inst) !MCValue {
+        if (inst.cast(ir.Inst.Constant)) |const_inst| {
+            switch (inst.ty.zigTypeTag()) {
+                .Int => {
+                    const info = inst.ty.intInfo(self.module.target);
+                    const ptr_bits = self.module.target.cpu.arch.ptrBitWidth();
+                    if (info.bits > ptr_bits or info.signed) {
+                        return self.fail(inst.src, "TODO const int bigger than ptr and signed int", .{});
+                    }
+                    return MCValue{ .immediate = const_inst.val.toUnsignedInt() };
+                },
+                else => return self.fail(inst.src, "TODO implement const of type '{}'", .{inst.ty}),
+            }
+        } else {
+            return self.inst_table.getValue(inst).?;
+        }
     }
-    return try renderLoad(ofile, ptr, ptr_type, "");
-}
 
-pub fn renderStoreUntyped(
-    ofile: *ObjectFile,
-    value: *llvm.Value,
-    ptr: *llvm.Value,
-    alignment: Type.Pointer.Align,
-    vol: Type.Pointer.Vol,
-) !*llvm.Value {
-    const result = llvm.BuildStore(ofile.builder, value, ptr) orelse return error.OutOfMemory;
-    switch (vol) {
-        .Non => {},
-        .Volatile => llvm.SetVolatile(result, 1),
+    fn fail(self: *Function, src: usize, comptime format: []const u8, args: var) error{ CodegenFail, OutOfMemory } {
+        @setCold(true);
+        const msg = try std.fmt.allocPrint(self.errors.allocator, format, args);
+        {
+            errdefer self.errors.allocator.free(msg);
+            (try self.errors.addOne()).* = .{
+                .byte_offset = src,
+                .msg = msg,
+            };
+        }
+        return error.CodegenFail;
     }
-    llvm.SetAlignment(result, resolveAlign(ofile, alignment, llvm.TypeOf(value)));
-    return result;
-}
-
-pub fn renderStore(
-    ofile: *ObjectFile,
-    value: *llvm.Value,
-    ptr: *llvm.Value,
-    ptr_type: *Type.Pointer,
-) !*llvm.Value {
-    return renderStoreUntyped(ofile, value, ptr, ptr_type.key.alignment, ptr_type.key.vol);
-}
-
-pub fn renderAlloca(
-    ofile: *ObjectFile,
-    var_type: *Type,
-    name: []const u8,
-    alignment: Type.Pointer.Align,
-) !*llvm.Value {
-    const llvm_var_type = try var_type.getLlvmType(ofile.arena, ofile.context);
-    const name_with_null = try std.cstr.addNullByte(ofile.arena, name);
-    const result = llvm.BuildAlloca(ofile.builder, llvm_var_type, @ptrCast([*:0]const u8, name_with_null.ptr)) orelse return error.OutOfMemory;
-    llvm.SetAlignment(result, resolveAlign(ofile, alignment, llvm_var_type));
-    return result;
-}
-
-pub fn resolveAlign(ofile: *ObjectFile, alignment: Type.Pointer.Align, llvm_type: *llvm.Type) u32 {
-    return switch (alignment) {
-        .Abi => return llvm.ABIAlignmentOfType(ofile.comp.target_data_ref, llvm_type),
-        .Override => |a| a,
-    };
-}
+};
src-self-hosted/ir.zig
@@ -724,7 +724,16 @@ pub fn main() anyerror!void {
     }
 
     const link = @import("link.zig");
-    try link.updateExecutableFilePath(allocator, analyzed_module, std.fs.cwd(), "a.out");
+    var result = try link.updateExecutableFilePath(allocator, analyzed_module, std.fs.cwd(), "a.out");
+    defer result.deinit(allocator);
+    if (result.errors.len != 0) {
+        for (result.errors) |err_msg| {
+            const loc = findLineColumn(source, err_msg.byte_offset);
+            std.debug.warn("{}:{}:{}: error: {}\n", .{ src_path, loc.line + 1, loc.column + 1, err_msg.msg });
+        }
+        if (debug_error_trace) return error.ParseFailure;
+        std.process.exit(1);
+    }
 }
 
 fn findLineColumn(source: []const u8, byte_offset: usize) struct { line: usize, column: usize } {
src-self-hosted/link.zig
@@ -5,15 +5,38 @@ const Allocator = std.mem.Allocator;
 const ir = @import("ir.zig");
 const fs = std.fs;
 const elf = std.elf;
+const codegen = @import("codegen.zig");
 
 const executable_mode = 0o755;
 const default_entry_addr = 0x8000000;
 
+pub const ErrorMsg = struct {
+    byte_offset: usize,
+    msg: []const u8,
+};
+
+pub const Result = struct {
+    errors: []ErrorMsg,
+
+    pub fn deinit(self: *Result, allocator: *mem.Allocator) void {
+        for (self.errors) |err| {
+            allocator.free(err.msg);
+        }
+        allocator.free(self.errors);
+        self.* = undefined;
+    }
+};
+
 /// Attempts incremental linking, if the file already exists.
 /// If incremental linking fails, falls back to truncating the file and rewriting it.
 /// A malicious file is detected as incremental link failure and does not cause Illegal Behavior.
 /// This operation is not atomic.
-pub fn updateExecutableFilePath(allocator: *Allocator, module: ir.Module, dir: fs.Dir, sub_path: []const u8) !void {
+pub fn updateExecutableFilePath(
+    allocator: *Allocator,
+    module: ir.Module,
+    dir: fs.Dir,
+    sub_path: []const u8,
+) !Result {
     const file = try dir.createFile(sub_path, .{ .truncate = false, .read = true, .mode = executable_mode });
     defer file.close();
 
@@ -21,12 +44,18 @@ pub fn updateExecutableFilePath(allocator: *Allocator, module: ir.Module, dir: f
 }
 
 /// Atomically overwrites the old file, if present.
-pub fn writeExecutableFilePath(allocator: *Allocator, module: ir.Module, dir: fs.Dir, sub_path: []const u8) !void {
+pub fn writeExecutableFilePath(
+    allocator: *Allocator,
+    module: ir.Module,
+    dir: fs.Dir,
+    sub_path: []const u8,
+) !Result {
     const af = try dir.atomicFile(sub_path, .{ .mode = executable_mode });
     defer af.deinit();
 
-    try writeExecutableFile(allocator, module, af.file);
+    const result = try writeExecutableFile(allocator, module, af.file);
     try af.finish();
+    return result;
 }
 
 /// Attempts incremental linking, if the file already exists.
@@ -34,8 +63,8 @@ pub fn writeExecutableFilePath(allocator: *Allocator, module: ir.Module, dir: fs
 /// Returns an error if `file` is not already open with +read +write +seek abilities.
 /// A malicious file is detected as incremental link failure and does not cause Illegal Behavior.
 /// This operation is not atomic.
-pub fn updateExecutableFile(allocator: *Allocator, module: ir.Module, file: fs.File) !void {
-    updateExecutableFileInner(allocator, module, file) catch |err| switch (err) {
+pub fn updateExecutableFile(allocator: *Allocator, module: ir.Module, file: fs.File) !Result {
+    return updateExecutableFileInner(allocator, module, file) catch |err| switch (err) {
         error.IncrFailed => {
             return writeExecutableFile(allocator, module, file);
         },
@@ -66,20 +95,17 @@ const Update = struct {
     text_section_index: ?u16,
     symtab_section_index: ?u16,
 
-    /// Key: index into strtab. Value: index into symbols.
-    symbol_table: std.AutoHashMap(usize, usize),
     /// The same order as in the file
     symbols: std.ArrayList(elf.Elf64_Sym),
-    /// Sorted by address, index into symbols
-    symbols_by_addr: std.ArrayList(usize),
+
+    errors: std.ArrayList(ErrorMsg),
 
     fn deinit(self: *Update) void {
         self.sections.deinit();
         self.program_headers.deinit();
         self.shstrtab.deinit();
-        self.symbol_table.deinit();
         self.symbols.deinit();
-        self.symbols_by_addr.deinit();
+        self.errors.deinit();
     }
 
     // `expand_num / expand_den` is the factor of padding when allocation
@@ -162,6 +188,7 @@ const Update = struct {
     fn makeString(self: *Update, bytes: []const u8) !u32 {
         const result = self.shstrtab.items.len;
         try self.shstrtab.appendSlice(bytes);
+        try self.shstrtab.append(0);
         return @intCast(u32, result);
     }
 
@@ -187,6 +214,7 @@ const Update = struct {
             const file_size = 256 * 1024;
             const p_align = 0x1000;
             const off = self.findFreeSpace(file_size, p_align);
+            //std.debug.warn("found PT_LOAD free space 0x{x} to 0x{x}\n", .{ off, off + file_size });
             try self.program_headers.append(.{
                 .p_type = elf.PT_LOAD,
                 .p_offset = off,
@@ -194,10 +222,10 @@ const Update = struct {
                 .p_vaddr = default_entry_addr,
                 .p_paddr = default_entry_addr,
                 .p_memsz = 0,
-                .p_align = 0x1000,
+                .p_align = p_align,
                 .p_flags = elf.PF_X | elf.PF_R,
             });
-            self.entry_addr = default_entry_addr;
+            self.entry_addr = null;
             phdr_load_re_dirty = true;
             phdr_table_dirty = true;
         }
@@ -220,6 +248,7 @@ const Update = struct {
         if (self.shstrtab_index == null) {
             self.shstrtab_index = @intCast(u16, self.sections.items.len);
             const off = self.findFreeSpace(self.shstrtab.items.len, 1);
+            //std.debug.warn("found shstrtab free space 0x{x} to 0x{x}\n", .{ off, off + self.shstrtab.items.len });
             try self.sections.append(.{
                 .sh_name = try self.makeString(".shstrtab"),
                 .sh_type = elf.SHT_STRTAB,
@@ -259,6 +288,7 @@ const Update = struct {
             const each_size: u64 = if (small_ptr) @sizeOf(elf.Elf32_Sym) else @sizeOf(elf.Elf64_Sym);
             const file_size = self.module.exports.len * each_size;
             const off = self.findFreeSpace(file_size, min_align);
+            //std.debug.warn("found symtab free space 0x{x} to 0x{x}\n", .{ off, off + file_size });
 
             try self.sections.append(.{
                 .sh_name = try self.makeString(".symtab"),
@@ -307,6 +337,7 @@ const Update = struct {
             const needed_size = self.program_headers.items.len * phsize;
 
             if (needed_size > allocated_size) {
+                self.phdr_table_offset = null; // free the space
                 self.phdr_table_offset = self.findFreeSpace(needed_size, phalign);
             }
 
@@ -361,6 +392,7 @@ const Update = struct {
             const needed_size = self.sections.items.len * phsize;
 
             if (needed_size > allocated_size) {
+                self.shdr_table_offset = null; // free the space
                 self.shdr_table_offset = self.findFreeSpace(needed_size, phalign);
             }
 
@@ -414,11 +446,30 @@ const Update = struct {
                 },
             }
         }
-        if (shstrtab_dirty) {
-            try self.file.pwriteAll(self.shstrtab.items, self.sections.items[self.shstrtab_index.?].sh_offset);
-        }
         try self.writeCodeAndSymbols();
-        try self.writeElfHeader();
+
+        const shstrtab_sect = &self.sections.items[self.shstrtab_index.?];
+        if (shstrtab_dirty or self.shstrtab.items.len != shstrtab_sect.sh_size) {
+            const allocated_size = self.allocatedSize(shstrtab_sect.sh_offset);
+            const needed_size = self.shstrtab.items.len;
+
+            if (needed_size > allocated_size) {
+                shstrtab_sect.sh_size = 0; // free the space
+                shstrtab_sect.sh_offset = self.findFreeSpace(needed_size, 1);
+                shstrtab_sect.sh_size = needed_size;
+            }
+            try self.file.pwriteAll(self.shstrtab.items, shstrtab_sect.sh_offset);
+        }
+        if (self.entry_addr == null) {
+            const msg = try std.fmt.allocPrint(self.errors.allocator, "no entry point found", .{});
+            errdefer self.errors.allocator.free(msg);
+            try self.errors.append(.{
+                .byte_offset = 0,
+                .msg = msg,
+            });
+        } else {
+            try self.writeElfHeader();
+        }
         // TODO find end pos and truncate
     }
 
@@ -540,13 +591,122 @@ const Update = struct {
     }
 
     fn writeCodeAndSymbols(self: *Update) !void {
-        @panic("TODO writeCodeAndSymbols");
+        // index 0 is always a null symbol
+        try self.symbols.resize(1);
+        self.symbols.items[0] = .{
+            .st_name = 0,
+            .st_info = 0,
+            .st_other = 0,
+            .st_shndx = 0,
+            .st_value = 0,
+            .st_size = 0,
+        };
+
+        const phdr = &self.program_headers.items[self.phdr_load_re_index.?];
+        var vaddr: u64 = phdr.p_vaddr;
+
+        var code = std.ArrayList(u8).init(self.sections.allocator);
+        defer code.deinit();
+
+        for (self.module.exports) |exp| {
+            code.shrink(0);
+            var symbol = try codegen.generateSymbol(exp.typed_value, self.module.*, &code);
+            defer symbol.deinit(code.allocator);
+            if (symbol.errors.len != 0) {
+                for (symbol.errors) |err| {
+                    const msg = try mem.dupe(self.errors.allocator, u8, err.msg);
+                    errdefer self.errors.allocator.free(msg);
+                    try self.errors.append(.{
+                        .byte_offset = err.byte_offset,
+                        .msg = msg,
+                    });
+                }
+                continue;
+            }
+
+            if (mem.eql(u8, exp.name, "_start")) {
+                self.entry_addr = vaddr;
+            }
+            (try self.symbols.addOne()).* = .{
+                .st_name = try self.makeString(exp.name),
+                .st_info = (elf.STB_LOCAL << 4) | elf.STT_FUNC,
+                .st_other = 0,
+                .st_shndx = self.text_section_index.?,
+                .st_value = vaddr,
+                .st_size = code.items.len,
+            };
+            vaddr += code.items.len;
+        }
+
+        return self.writeSymbols();
+    }
+
+    fn writeSymbols(self: *Update) !void {
+        const ptr_width: enum { p32, p64 } = switch (self.module.target.cpu.arch.ptrBitWidth()) {
+            32 => .p32,
+            64 => .p64,
+            else => return error.UnsupportedArchitecture,
+        };
+        const small_ptr = ptr_width == .p32;
+        const syms_sect = &self.sections.items[self.symtab_section_index.?];
+        const sym_align: u16 = if (small_ptr) @alignOf(elf.Elf32_Sym) else @alignOf(elf.Elf64_Sym);
+        const sym_size: u64 = if (small_ptr) @sizeOf(elf.Elf32_Sym) else @sizeOf(elf.Elf64_Sym);
+
+        const allocated_size = self.allocatedSize(syms_sect.sh_offset);
+        const needed_size = self.symbols.items.len * sym_size;
+        if (needed_size > allocated_size) {
+            syms_sect.sh_size = 0; // free the space
+            syms_sect.sh_offset = self.findFreeSpace(needed_size, sym_align);
+            syms_sect.sh_size = needed_size;
+        }
+        const allocator = self.symbols.allocator;
+        const foreign_endian = self.module.target.cpu.arch.endian() != std.Target.current.cpu.arch.endian();
+        switch (ptr_width) {
+            .p32 => {
+                const buf = try allocator.alloc(elf.Elf32_Sym, self.symbols.items.len);
+                defer allocator.free(buf);
+
+                for (buf) |*sym, i| {
+                    sym.* = .{
+                        .st_name = self.symbols.items[i].st_name,
+                        .st_value = @intCast(u32, self.symbols.items[i].st_value),
+                        .st_size = @intCast(u32, self.symbols.items[i].st_size),
+                        .st_info = self.symbols.items[i].st_info,
+                        .st_other = self.symbols.items[i].st_other,
+                        .st_shndx = self.symbols.items[i].st_shndx,
+                    };
+                    if (foreign_endian) {
+                        bswapAllFields(elf.Elf32_Sym, sym);
+                    }
+                }
+                try self.file.pwriteAll(mem.sliceAsBytes(buf), syms_sect.sh_offset);
+            },
+            .p64 => {
+                const buf = try allocator.alloc(elf.Elf64_Sym, self.symbols.items.len);
+                defer allocator.free(buf);
+
+                for (buf) |*sym, i| {
+                    sym.* = .{
+                        .st_name = self.symbols.items[i].st_name,
+                        .st_value = self.symbols.items[i].st_value,
+                        .st_size = self.symbols.items[i].st_size,
+                        .st_info = self.symbols.items[i].st_info,
+                        .st_other = self.symbols.items[i].st_other,
+                        .st_shndx = self.symbols.items[i].st_shndx,
+                    };
+                    if (foreign_endian) {
+                        bswapAllFields(elf.Elf64_Sym, sym);
+                    }
+                }
+                try self.file.pwriteAll(mem.sliceAsBytes(buf), syms_sect.sh_offset);
+            },
+        }
     }
 };
 
 /// Truncates the existing file contents and overwrites the contents.
 /// Returns an error if `file` is not already open with +read +write +seek abilities.
-pub fn writeExecutableFile(allocator: *Allocator, module: ir.Module, file: fs.File) !void {
+pub fn writeExecutableFile(allocator: *Allocator, module: ir.Module, file: fs.File) !Result {
     var update = Update{
         .file = file,
         .module = &module,
@@ -561,17 +721,20 @@ pub fn writeExecutableFile(allocator: *Allocator, module: ir.Module, file: fs.Fi
         .text_section_index = null,
         .symtab_section_index = null,
 
-        .symbol_table = std.AutoHashMap(usize, usize).init(allocator),
         .symbols = std.ArrayList(elf.Elf64_Sym).init(allocator),
-        .symbols_by_addr = std.ArrayList(usize).init(allocator),
+
+        .errors = std.ArrayList(ErrorMsg).init(allocator),
     };
     defer update.deinit();
 
-    return update.perform();
+    try update.perform();
+    return Result{
+        .errors = update.errors.toOwnedSlice(),
+    };
 }
 
 /// Returns error.IncrFailed if incremental update could not be performed.
-fn updateExecutableFileInner(allocator: *Allocator, module: ir.Module, file: fs.File) !void {
+fn updateExecutableFileInner(allocator: *Allocator, module: ir.Module, file: fs.File) !Result {
     //var ehdr_buf: [@sizeOf(elf.Elf64_Ehdr)]u8 = undefined;
 
     // TODO implement incremental linking
src-self-hosted/value.zig
@@ -264,6 +264,56 @@ pub const Value = extern union {
         }
     }
 
+    /// Asserts the value is an integer and it fits in a u64
+    pub fn toUnsignedInt(self: Value) u64 {
+        switch (self.tag()) {
+            .ty,
+            .u8_type,
+            .i8_type,
+            .isize_type,
+            .usize_type,
+            .c_short_type,
+            .c_ushort_type,
+            .c_int_type,
+            .c_uint_type,
+            .c_long_type,
+            .c_ulong_type,
+            .c_longlong_type,
+            .c_ulonglong_type,
+            .c_longdouble_type,
+            .f16_type,
+            .f32_type,
+            .f64_type,
+            .f128_type,
+            .c_void_type,
+            .bool_type,
+            .void_type,
+            .type_type,
+            .anyerror_type,
+            .comptime_int_type,
+            .comptime_float_type,
+            .noreturn_type,
+            .fn_naked_noreturn_no_args_type,
+            .single_const_pointer_to_comptime_int_type,
+            .const_slice_u8_type,
+            .void_value,
+            .noreturn_value,
+            .bool_true,
+            .bool_false,
+            .function,
+            .ref,
+            .ref_val,
+            .bytes,
+            => unreachable,
+
+            .zero => return 0,
+
+            .int_u64 => return self.cast(Payload.Int_u64).?.int,
+            .int_i64 => return @intCast(u64, self.cast(Payload.Int_u64).?.int),
+            .int_big => return self.cast(Payload.IntBig).?.big_int.to(u64) catch unreachable,
+        }
+    }
+
     /// Asserts the value is an integer, and the destination type is ComptimeInt or Int.
     pub fn intFitsInType(self: Value, ty: Type, target: Target) bool {
         switch (self.tag()) {