x86_64: implement error name

6 files changed, 529 insertions, 36 deletions

diff --git a/src/arch/x86_64/CodeGen.zig b/src/arch/x86_64/CodeGen.zig
index 45d8547082..684724f68e 100644
--- a/src/arch/x86_64/CodeGen.zig
+++ b/src/arch/x86_64/CodeGen.zig
@@ -1923,7 +1923,7 @@ fn genSetStackTruncatedOverflowCompare(
     );
 
     try self.genSetStack(ty, stack_offset, .{ .register = scratch_reg }, .{});
-    try self.genSetStack(Type.initTag(.u1), stack_offset - overflow_bit_offset, .{
+    try self.genSetStack(Type.u1, stack_offset - overflow_bit_offset, .{
         .register = overflow_reg.to8(),
     }, .{});
 }
@@ -5280,8 +5280,7 @@ fn airCall(self: *Self, inst: Air.Inst.Index, modifier: std.builtin.CallModifier
 
             if (self.bin_file.cast(link.File.Elf)) |elf_file| {
                 const atom_index = try elf_file.getOrCreateAtomForDecl(func.owner_decl);
-                const atom = elf_file.getAtom(atom_index);
-                const got_addr = atom.getOffsetTableAddress(elf_file);
+                const got_addr = elf_file.getAtom(atom_index).getOffsetTableAddress(elf_file);
                 try self.asmMemory(.call, Memory.sib(.qword, .{
                     .base = .ds,
                     .disp = @intCast(i32, got_addr),
@@ -5289,22 +5288,18 @@ fn airCall(self: *Self, inst: Air.Inst.Index, modifier: std.builtin.CallModifier
             } else if (self.bin_file.cast(link.File.Coff)) |coff_file| {
                 const atom_index = try coff_file.getOrCreateAtomForDecl(func.owner_decl);
                 const sym_index = coff_file.getAtom(atom_index).getSymbolIndex().?;
-                try self.genSetReg(Type.initTag(.usize), .rax, .{
-                    .linker_load = .{
-                        .type = .got,
-                        .sym_index = sym_index,
-                    },
-                });
+                try self.genSetReg(Type.usize, .rax, .{ .linker_load = .{
+                    .type = .got,
+                    .sym_index = sym_index,
+                } });
                 try self.asmRegister(.call, .rax);
             } else if (self.bin_file.cast(link.File.MachO)) |macho_file| {
                 const atom_index = try macho_file.getOrCreateAtomForDecl(func.owner_decl);
                 const sym_index = macho_file.getAtom(atom_index).getSymbolIndex().?;
-                try self.genSetReg(Type.initTag(.usize), .rax, .{
-                    .linker_load = .{
-                        .type = .got,
-                        .sym_index = sym_index,
-                    },
-                });
+                try self.genSetReg(Type.usize, .rax, .{ .linker_load = .{
+                    .type = .got,
+                    .sym_index = sym_index,
+                } });
                 try self.asmRegister(.call, .rax);
             } else if (self.bin_file.cast(link.File.Plan9)) |p9| {
                 const decl_block_index = try p9.seeDecl(func.owner_decl);
@@ -5325,7 +5320,7 @@ fn airCall(self: *Self, inst: Air.Inst.Index, modifier: std.builtin.CallModifier
             const lib_name = mem.sliceTo(extern_fn.lib_name, 0);
             if (self.bin_file.cast(link.File.Coff)) |coff_file| {
                 const sym_index = try coff_file.getGlobalSymbol(decl_name, lib_name);
-                try self.genSetReg(Type.initTag(.usize), .rax, .{
+                try self.genSetReg(Type.usize, .rax, .{
                     .linker_load = .{
                         .type = .import,
                         .sym_index = sym_index,
@@ -5353,7 +5348,7 @@ fn airCall(self: *Self, inst: Air.Inst.Index, modifier: std.builtin.CallModifier
     } else {
         assert(ty.zigTypeTag() == .Pointer);
         const mcv = try self.resolveInst(callee);
-        try self.genSetReg(Type.initTag(.usize), .rax, mcv);
+        try self.genSetReg(Type.usize, .rax, mcv);
         try self.asmRegister(.call, .rax);
     }
 
@@ -7299,7 +7294,7 @@ fn airArrayToSlice(self: *Self, inst: Air.Inst.Index) !void {
     const result: MCValue = if (self.liveness.isUnused(inst)) .dead else blk: {
         const stack_offset = @intCast(i32, try self.allocMem(inst, 16, 16));
         try self.genSetStack(ptr_ty, stack_offset, ptr, .{});
-        try self.genSetStack(Type.initTag(.u64), stack_offset - 8, .{ .immediate = array_len }, .{});
+        try self.genSetStack(Type.u64, stack_offset - 8, .{ .immediate = array_len }, .{});
         break :blk .{ .stack_offset = stack_offset };
     };
     return self.finishAir(inst, result, .{ ty_op.operand, .none, .none });
@@ -7809,10 +7804,92 @@ fn airTagName(self: *Self, inst: Air.Inst.Index) !void {
 
 fn airErrorName(self: *Self, inst: Air.Inst.Index) !void {
     const un_op = self.air.instructions.items(.data)[inst].un_op;
-    const operand = try self.resolveInst(un_op);
-    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else {
-        _ = operand;
-        return self.fail("TODO implement airErrorName for x86_64", .{});
+    const result: MCValue = if (self.liveness.isUnused(inst)) .dead else result: {
+        const err_ty = self.air.typeOf(un_op);
+        const err_mcv = try self.resolveInst(un_op);
+        const err_reg = try self.copyToTmpRegister(err_ty, err_mcv);
+        const err_lock = self.register_manager.lockRegAssumeUnused(err_reg);
+        defer self.register_manager.unlockReg(err_lock);
+
+        const addr_reg = try self.register_manager.allocReg(null, gp);
+        const addr_lock = self.register_manager.lockRegAssumeUnused(addr_reg);
+        defer self.register_manager.unlockReg(addr_lock);
+
+        if (self.bin_file.cast(link.File.Elf)) |elf_file| {
+            const atom_index = try elf_file.getOrCreateAtomForLazySymbol(
+                .{ .kind = .const_data, .ty = Type.anyerror },
+                4, // dword alignment
+            );
+            const got_addr = elf_file.getAtom(atom_index).getOffsetTableAddress(elf_file);
+            try self.asmRegisterMemory(.mov, addr_reg.to64(), Memory.sib(.qword, .{
+                .base = .ds,
+                .disp = @intCast(i32, got_addr),
+            }));
+        } else if (self.bin_file.cast(link.File.Coff)) |coff_file| {
+            const atom_index = try coff_file.getOrCreateAtomForLazySymbol(
+                .{ .kind = .const_data, .ty = Type.anyerror },
+                4, // dword alignment
+            );
+            const sym_index = coff_file.getAtom(atom_index).getSymbolIndex().?;
+            try self.genSetReg(Type.usize, addr_reg, .{ .linker_load = .{
+                .type = .got,
+                .sym_index = sym_index,
+            } });
+        } else if (self.bin_file.cast(link.File.MachO)) |macho_file| {
+            const atom_index = try macho_file.getOrCreateAtomForLazySymbol(
+                .{ .kind = .const_data, .ty = Type.anyerror },
+                4, // dword alignment
+            );
+            const sym_index = macho_file.getAtom(atom_index).getSymbolIndex().?;
+            try self.genSetReg(Type.usize, addr_reg, .{ .linker_load = .{
+                .type = .got,
+                .sym_index = sym_index,
+            } });
+        } else {
+            return self.fail("TODO implement airErrorName for x86_64 {s}", .{@tagName(self.bin_file.tag)});
+        }
+
+        const start_reg = try self.register_manager.allocReg(null, gp);
+        const start_lock = self.register_manager.lockRegAssumeUnused(start_reg);
+        defer self.register_manager.unlockReg(start_lock);
+
+        const end_reg = try self.register_manager.allocReg(null, gp);
+        const end_lock = self.register_manager.lockRegAssumeUnused(end_reg);
+        defer self.register_manager.unlockReg(end_lock);
+
+        try self.truncateRegister(err_ty, err_reg.to32());
+
+        try self.asmRegisterMemory(.mov, start_reg.to32(), Memory.sib(.dword, .{
+            .base = addr_reg.to64(),
+            .scale_index = .{ .scale = 4, .index = err_reg.to64() },
+            .disp = 0,
+        }));
+        try self.asmRegisterMemory(.mov, end_reg.to32(), Memory.sib(.dword, .{
+            .base = addr_reg.to64(),
+            .scale_index = .{ .scale = 4, .index = err_reg.to64() },
+            .disp = 4,
+        }));
+        try self.asmRegisterRegister(.sub, end_reg.to32(), start_reg.to32());
+        try self.asmRegisterMemory(.lea, start_reg.to64(), Memory.sib(.byte, .{
+            .base = addr_reg.to64(),
+            .scale_index = .{ .scale = 1, .index = start_reg.to64() },
+            .disp = 0,
+        }));
+        try self.asmRegisterMemory(.lea, end_reg.to32(), Memory.sib(.byte, .{
+            .base = end_reg.to64(),
+            .disp = -1,
+        }));
+
+        const dst_mcv = try self.allocRegOrMem(inst, false);
+        try self.asmMemoryRegister(.mov, Memory.sib(.qword, .{
+            .base = .rbp,
+            .disp = 0 - dst_mcv.stack_offset,
+        }), start_reg.to64());
+        try self.asmMemoryRegister(.mov, Memory.sib(.qword, .{
+            .base = .rbp,
+            .disp = 8 - dst_mcv.stack_offset,
+        }), end_reg.to64());
+        break :result dst_mcv;
     };
     return self.finishAir(inst, result, .{ un_op, .none, .none });
 }
@@ -8046,7 +8123,7 @@ fn limitImmediateType(self: *Self, operand: Air.Inst.Ref, comptime T: type) !MCV
             // This immediate is unsigned.
             const U = std.meta.Int(.unsigned, ti.bits - @boolToInt(ti.signedness == .signed));
             if (imm >= math.maxInt(U)) {
-                return MCValue{ .register = try self.copyToTmpRegister(Type.initTag(.usize), mcv) };
+                return MCValue{ .register = try self.copyToTmpRegister(Type.usize, mcv) };
             }
         },
         else => {},
@@ -8321,8 +8398,8 @@ fn truncateRegister(self: *Self, ty: Type, reg: Register) !void {
         .unsigned => {
             const shift = @intCast(u6, max_reg_bit_width - int_info.bits);
             const mask = (~@as(u64, 0)) >> shift;
-            if (int_info.bits < 32) {
-                try self.genBinOpMir(.@"and", Type.usize, .{ .register = reg }, .{ .immediate = mask });
+            if (int_info.bits <= 32) {
+                try self.genBinOpMir(.@"and", Type.u32, .{ .register = reg }, .{ .immediate = mask });
             } else {
                 const tmp_reg = try self.copyToTmpRegister(Type.usize, .{ .immediate = mask });
                 try self.genBinOpMir(.@"and", Type.usize, .{ .register = reg }, .{ .register = tmp_reg });
diff --git a/src/codegen.zig b/src/codegen.zig
index a99ff18dfd..67ada2fedd 100644
--- a/src/codegen.zig
+++ b/src/codegen.zig
@@ -99,6 +99,47 @@ fn writeFloat(comptime F: type, f: F, target: Target, endian: std.builtin.Endian
     mem.writeInt(Int, code[0..@sizeOf(Int)], int, endian);
 }
 
+pub fn generateLazySymbol(
+    bin_file: *link.File,
+    src_loc: Module.SrcLoc,
+    lazy_sym: link.File.LazySymbol,
+    code: *std.ArrayList(u8),
+    debug_output: DebugInfoOutput,
+    reloc_info: RelocInfo,
+) CodeGenError!Result {
+    _ = debug_output;
+    _ = reloc_info;
+
+    const tracy = trace(@src());
+    defer tracy.end();
+
+    const target = bin_file.options.target;
+    const endian = target.cpu.arch.endian();
+
+    const mod = bin_file.options.module.?;
+    log.debug("generateLazySymbol: kind = {s}, ty = {}", .{
+        @tagName(lazy_sym.kind),
+        lazy_sym.ty.fmt(mod),
+    });
+
+    if (lazy_sym.kind == .const_data and lazy_sym.ty.isAnyError()) {
+        const err_names = mod.error_name_list.items;
+        try code.resize(err_names.len * 4);
+        for (err_names, 0..) |err_name, index| {
+            mem.writeInt(u32, code.items[index * 4 ..][0..4], @intCast(u32, code.items.len), endian);
+            try code.ensureUnusedCapacity(err_name.len + 1);
+            code.appendSliceAssumeCapacity(err_name);
+            code.appendAssumeCapacity(0);
+        }
+        return Result.ok;
+    } else return .{ .fail = try ErrorMsg.create(
+        bin_file.allocator,
+        src_loc,
+        "TODO implement generateLazySymbol for {s} {}",
+        .{ @tagName(lazy_sym.kind), lazy_sym.ty.fmt(mod) },
+    ) };
+}
+
 pub fn generateSymbol(
     bin_file: *link.File,
     src_loc: Module.SrcLoc,
@@ -118,9 +159,10 @@ pub fn generateSymbol(
     const target = bin_file.options.target;
     const endian = target.cpu.arch.endian();
 
+    const mod = bin_file.options.module.?;
     log.debug("generateSymbol: ty = {}, val = {}", .{
-        typed_value.ty.fmtDebug(),
-        typed_value.val.fmtDebug(),
+        typed_value.ty.fmt(mod),
+        typed_value.val.fmtValue(typed_value.ty, mod),
     });
 
     if (typed_value.val.isUndefDeep()) {
@@ -170,7 +212,6 @@ pub fn generateSymbol(
             },
             .str_lit => {
                 const str_lit = typed_value.val.castTag(.str_lit).?.data;
-                const mod = bin_file.options.module.?;
                 const bytes = mod.string_literal_bytes.items[str_lit.index..][0..str_lit.len];
                 try code.ensureUnusedCapacity(bytes.len + 1);
                 code.appendSliceAssumeCapacity(bytes);
@@ -300,7 +341,6 @@ pub fn generateSymbol(
                 switch (container_ptr.tag()) {
                     .decl_ref => {
                         const decl_index = container_ptr.castTag(.decl_ref).?.data;
-                        const mod = bin_file.options.module.?;
                         const decl = mod.declPtr(decl_index);
                         const addend = blk: {
                             switch (decl.ty.zigTypeTag()) {
@@ -493,7 +533,6 @@ pub fn generateSymbol(
                 const field_vals = typed_value.val.castTag(.aggregate).?.data;
                 const abi_size = math.cast(usize, typed_value.ty.abiSize(target)) orelse return error.Overflow;
                 const current_pos = code.items.len;
-                const mod = bin_file.options.module.?;
                 try code.resize(current_pos + abi_size);
                 var bits: u16 = 0;
 
@@ -570,7 +609,6 @@ pub fn generateSymbol(
             }
 
             const union_ty = typed_value.ty.cast(Type.Payload.Union).?.data;
-            const mod = bin_file.options.module.?;
             const field_index = typed_value.ty.unionTagFieldIndex(union_obj.tag, mod).?;
             assert(union_ty.haveFieldTypes());
             const field_ty = union_ty.fields.values()[field_index].ty;
@@ -776,7 +814,6 @@ pub fn generateSymbol(
             },
             .str_lit => {
                 const str_lit = typed_value.val.castTag(.str_lit).?.data;
-                const mod = bin_file.options.module.?;
                 const bytes = mod.string_literal_bytes.items[str_lit.index..][0..str_lit.len];
                 try code.ensureUnusedCapacity(str_lit.len);
                 code.appendSliceAssumeCapacity(bytes);
diff --git a/src/link.zig b/src/link.zig
index 05519ba6b5..7ca94f4f6d 100644
--- a/src/link.zig
+++ b/src/link.zig
@@ -687,6 +687,7 @@ pub const File = struct {
         FrameworkNotFound,
         FunctionSignatureMismatch,
         GlobalTypeMismatch,
+        HotSwapUnavailableOnHostOperatingSystem,
         InvalidCharacter,
         InvalidEntryKind,
         InvalidFeatureSet,
@@ -1104,6 +1105,26 @@ pub const File = struct {
         missing_libc: bool = false,
     };
 
+    pub const LazySymbol = struct {
+        kind: enum { code, const_data },
+        ty: Type,
+
+        pub const Context = struct {
+            mod: *Module,
+
+            pub fn hash(ctx: @This(), sym: LazySymbol) u32 {
+                var hasher = std.hash.Wyhash.init(0);
+                std.hash.autoHash(&hasher, sym.kind);
+                sym.ty.hashWithHasher(&hasher, ctx.mod);
+                return @truncate(u32, hasher.final());
+            }
+
+            pub fn eql(ctx: @This(), lhs: LazySymbol, rhs: LazySymbol, _: usize) bool {
+                return lhs.kind == rhs.kind and lhs.ty.eql(rhs.ty, ctx.mod);
+            }
+        };
+    };
+
     pub const C = @import("link/C.zig");
     pub const Coff = @import("link/Coff.zig");
     pub const Plan9 = @import("link/Plan9.zig");
diff --git a/src/link/Coff.zig b/src/link/Coff.zig
index f3068f01a9..800f96e90c 100644
--- a/src/link/Coff.zig
+++ b/src/link/Coff.zig
@@ -49,6 +49,9 @@ imports_count_dirty: bool = true,
 /// Virtual address of the entry point procedure relative to image base.
 entry_addr: ?u32 = null,
 
+/// Table of tracked LazySymbols.
+lazy_syms: LazySymbolTable = .{},
+
 /// Table of tracked Decls.
 decls: std.AutoArrayHashMapUnmanaged(Module.Decl.Index, DeclMetadata) = .{},
 
@@ -142,6 +145,18 @@ const Section = struct {
     free_list: std.ArrayListUnmanaged(Atom.Index) = .{},
 };
 
+const LazySymbolTable = std.ArrayHashMapUnmanaged(
+    link.File.LazySymbol,
+    LazySymbolMetadata,
+    link.File.LazySymbol.Context,
+    true,
+);
+
+const LazySymbolMetadata = struct {
+    atom: Atom.Index,
+    section: u16,
+};
+
 const DeclMetadata = struct {
     atom: Atom.Index,
     section: u16,
@@ -1168,6 +1183,100 @@ pub fn updateDecl(self: *Coff, module: *Module, decl_index: Module.Decl.Index) !
     return self.updateDeclExports(module, decl_index, module.getDeclExports(decl_index));
 }
 
+fn updateLazySymbol(
+    self: *Coff,
+    lazy_sym: link.File.LazySymbol,
+    lazy_metadata: LazySymbolMetadata,
+) !void {
+    const gpa = self.base.allocator;
+    const mod = self.base.options.module.?;
+
+    var code_buffer = std.ArrayList(u8).init(gpa);
+    defer code_buffer.deinit();
+
+    const name = try std.fmt.allocPrint(gpa, "__lazy_{s}_{}", .{
+        @tagName(lazy_sym.kind),
+        lazy_sym.ty.fmt(mod),
+    });
+    defer gpa.free(name);
+
+    const atom_index = lazy_metadata.atom;
+    const atom = self.getAtomPtr(atom_index);
+    const local_sym_index = atom.getSymbolIndex().?;
+
+    const src = if (lazy_sym.ty.getOwnerDeclOrNull()) |owner_decl|
+        mod.declPtr(owner_decl).srcLoc()
+    else
+        Module.SrcLoc{
+            .file_scope = undefined,
+            .parent_decl_node = undefined,
+            .lazy = .unneeded,
+        };
+    const res = try codegen.generateLazySymbol(
+        &self.base,
+        src,
+        lazy_sym,
+        &code_buffer,
+        .none,
+        .{ .parent_atom_index = local_sym_index },
+    );
+    const code = switch (res) {
+        .ok => code_buffer.items,
+        .fail => |em| {
+            log.err("{s}", .{em.msg});
+            return error.CodegenFail;
+        },
+    };
+
+    const required_alignment = atom.alignment;
+    const code_len = @intCast(u32, code.len);
+    const symbol = atom.getSymbolPtr(self);
+    try self.setSymbolName(symbol, name);
+    symbol.section_number = @intToEnum(coff.SectionNumber, lazy_metadata.section + 1);
+    symbol.type = .{ .complex_type = .NULL, .base_type = .NULL };
+
+    const vaddr = try self.allocateAtom(atom_index, code_len, required_alignment);
+    errdefer self.freeAtom(atom_index);
+
+    log.debug("allocated atom for {s} at 0x{x}", .{ name, vaddr });
+    log.debug("  (required alignment 0x{x})", .{required_alignment});
+
+    atom.size = code_len;
+    symbol.value = vaddr;
+
+    const got_target = SymbolWithLoc{ .sym_index = local_sym_index, .file = null };
+    const got_index = try self.allocateGotEntry(got_target);
+    const got_atom_index = try self.createGotAtom(got_target);
+    const got_atom = self.getAtom(got_atom_index);
+    self.got_entries.items[got_index].sym_index = got_atom.getSymbolIndex().?;
+    try self.writePtrWidthAtom(got_atom_index);
+
+    self.markRelocsDirtyByTarget(atom.getSymbolWithLoc());
+    try self.writeAtom(atom_index, code);
+}
+
+pub fn getOrCreateAtomForLazySymbol(
+    self: *Coff,
+    lazy_sym: link.File.LazySymbol,
+    alignment: u32,
+) !Atom.Index {
+    const gop = try self.lazy_syms.getOrPutContext(self.base.allocator, lazy_sym, .{
+        .mod = self.base.options.module.?,
+    });
+    errdefer _ = self.lazy_syms.pop();
+    if (!gop.found_existing) {
+        gop.value_ptr.* = .{
+            .atom = try self.createAtom(),
+            .section = switch (lazy_sym.kind) {
+                .code => self.text_section_index.?,
+                .const_data => self.rdata_section_index.?,
+            },
+        };
+        self.getAtomPtr(gop.value_ptr.atom).alignment = alignment;
+    }
+    return gop.value_ptr.atom;
+}
+
 pub fn getOrCreateAtomForDecl(self: *Coff, decl_index: Module.Decl.Index) !Atom.Index {
     const gop = try self.decls.getOrPut(self.base.allocator, decl_index);
     if (!gop.found_existing) {
@@ -1498,6 +1607,19 @@ pub fn flushModule(self: *Coff, comp: *Compilation, prog_node: *std.Progress.Nod
     sub_prog_node.activate();
     defer sub_prog_node.end();
 
+    {
+        var lazy_it = self.lazy_syms.iterator();
+        while (lazy_it.next()) |lazy_entry| {
+            self.updateLazySymbol(
+                lazy_entry.key_ptr.*,
+                lazy_entry.value_ptr.*,
+            ) catch |err| switch (err) {
+                error.CodegenFail => return error.FlushFailure,
+                else => |e| return e,
+            };
+        }
+    }
+
     const gpa = self.base.allocator;
 
     while (self.unresolved.popOrNull()) |entry| {
diff --git a/src/link/Elf.zig b/src/link/Elf.zig
index 95104ec2e8..3b7c2efa0e 100644
--- a/src/link/Elf.zig
+++ b/src/link/Elf.zig
@@ -63,6 +63,12 @@ const Section = struct {
     free_list: std.ArrayListUnmanaged(Atom.Index) = .{},
 };
 
+const LazySymbolMetadata = struct {
+    atom: Atom.Index,
+    shdr: u16,
+    alignment: u32,
+};
+
 const DeclMetadata = struct {
     atom: Atom.Index,
     shdr: u16,
@@ -157,6 +163,9 @@ debug_line_header_dirty: bool = false,
 
 error_flags: File.ErrorFlags = File.ErrorFlags{},
 
+/// Table of tracked LazySymbols.
+lazy_syms: LazySymbolTable = .{},
+
 /// Table of tracked Decls.
 decls: std.AutoHashMapUnmanaged(Module.Decl.Index, DeclMetadata) = .{},
 
@@ -194,6 +203,7 @@ relocs: RelocTable = .{},
 
 const RelocTable = std.AutoHashMapUnmanaged(Atom.Index, std.ArrayListUnmanaged(Atom.Reloc));
 const UnnamedConstTable = std.AutoHashMapUnmanaged(Module.Decl.Index, std.ArrayListUnmanaged(Atom.Index));
+const LazySymbolTable = std.ArrayHashMapUnmanaged(File.LazySymbol, LazySymbolMetadata, File.LazySymbol.Context, true);
 
 /// When allocating, the ideal_capacity is calculated by
 /// actual_capacity + (actual_capacity / ideal_factor)
@@ -1011,6 +1021,19 @@ pub fn flushModule(self: *Elf, comp: *Compilation, prog_node: *std.Progress.Node
     sub_prog_node.activate();
     defer sub_prog_node.end();
 
+    {
+        var lazy_it = self.lazy_syms.iterator();
+        while (lazy_it.next()) |lazy_entry| {
+            self.updateLazySymbol(
+                lazy_entry.key_ptr.*,
+                lazy_entry.value_ptr.*,
+            ) catch |err| switch (err) {
+                error.CodegenFail => return error.FlushFailure,
+                else => |e| return e,
+            };
+        }
+    }
+
     // TODO This linker code currently assumes there is only 1 compilation unit and it
     // corresponds to the Zig source code.
     const module = self.base.options.module orelse return error.LinkingWithoutZigSourceUnimplemented;
@@ -2344,6 +2367,24 @@ pub fn freeDecl(self: *Elf, decl_index: Module.Decl.Index) void {
     }
 }
 
+pub fn getOrCreateAtomForLazySymbol(self: *Elf, lazy_sym: File.LazySymbol, alignment: u32) !Atom.Index {
+    const gop = try self.lazy_syms.getOrPutContext(self.base.allocator, lazy_sym, .{
+        .mod = self.base.options.module.?,
+    });
+    errdefer _ = self.lazy_syms.pop();
+    if (!gop.found_existing) {
+        gop.value_ptr.* = .{
+            .atom = try self.createAtom(),
+            .shdr = switch (lazy_sym.kind) {
+                .code => self.text_section_index.?,
+                .const_data => self.rodata_section_index.?,
+            },
+            .alignment = alignment,
+        };
+    }
+    return gop.value_ptr.atom;
+}
+
 pub fn getOrCreateAtomForDecl(self: *Elf, decl_index: Module.Decl.Index) !Atom.Index {
     const gop = try self.decls.getOrPut(self.base.allocator, decl_index);
     if (!gop.found_existing) {
@@ -2610,6 +2651,79 @@ pub fn updateDecl(self: *Elf, module: *Module, decl_index: Module.Decl.Index) !v
     return self.updateDeclExports(module, decl_index, module.getDeclExports(decl_index));
 }
 
+fn updateLazySymbol(self: *Elf, lazy_sym: File.LazySymbol, lazy_metadata: LazySymbolMetadata) !void {
+    const gpa = self.base.allocator;
+    const mod = self.base.options.module.?;
+
+    var code_buffer = std.ArrayList(u8).init(gpa);
+    defer code_buffer.deinit();
+
+    const name_str_index = blk: {
+        const name = try std.fmt.allocPrint(gpa, "__lazy_{s}_{}", .{
+            @tagName(lazy_sym.kind),
+            lazy_sym.ty.fmt(mod),
+        });
+        defer gpa.free(name);
+        break :blk try self.shstrtab.insert(gpa, name);
+    };
+    const name = self.shstrtab.get(name_str_index).?;
+
+    const atom_index = lazy_metadata.atom;
+    const atom = self.getAtom(atom_index);
+    const local_sym_index = atom.getSymbolIndex().?;
+
+    const src = if (lazy_sym.ty.getOwnerDeclOrNull()) |owner_decl|
+        mod.declPtr(owner_decl).srcLoc()
+    else
+        Module.SrcLoc{
+            .file_scope = undefined,
+            .parent_decl_node = undefined,
+            .lazy = .unneeded,
+        };
+    const res = try codegen.generateLazySymbol(
+        &self.base,
+        src,
+        lazy_sym,
+        &code_buffer,
+        .none,
+        .{ .parent_atom_index = local_sym_index },
+    );
+    const code = switch (res) {
+        .ok => code_buffer.items,
+        .fail => |em| {
+            log.err("{s}", .{em.msg});
+            return error.CodegenFail;
+        },
+    };
+
+    const shdr_index = lazy_metadata.shdr;
+    const phdr_index = self.sections.items(.phdr_index)[shdr_index];
+    const local_sym = atom.getSymbolPtr(self);
+    local_sym.* = .{
+        .st_name = name_str_index,
+        .st_info = (elf.STB_LOCAL << 4) | elf.STT_OBJECT,
+        .st_other = 0,
+        .st_shndx = shdr_index,
+        .st_value = 0,
+        .st_size = 0,
+    };
+    const required_alignment = lazy_metadata.alignment;
+    const vaddr = try self.allocateAtom(atom_index, code.len, required_alignment);
+    errdefer self.freeAtom(atom_index);
+    log.debug("allocated text block for {s} at 0x{x}", .{ name, vaddr });
+
+    self.offset_table.items[atom.offset_table_index] = vaddr;
+    local_sym.st_value = vaddr;
+    local_sym.st_size = code.len;
+
+    try self.writeSymbol(local_sym_index);
+    try self.writeOffsetTableEntry(atom.offset_table_index);
+
+    const section_offset = vaddr - self.program_headers.items[phdr_index].p_vaddr;
+    const file_offset = self.sections.items(.shdr)[shdr_index].sh_offset + section_offset;
+    try self.base.file.?.pwriteAll(code, file_offset);
+}
+
 pub fn lowerUnnamedConst(self: *Elf, typed_value: TypedValue, decl_index: Module.Decl.Index) !u32 {
     const gpa = self.base.allocator;
 
diff --git a/src/link/MachO.zig b/src/link/MachO.zig
index 4c3301a3b4..7840f5d89d 100644
--- a/src/link/MachO.zig
+++ b/src/link/MachO.zig
@@ -218,6 +218,9 @@ bindings: BindingTable = .{},
 /// this will be a table indexed by index into the list of Atoms.
 lazy_bindings: BindingTable = .{},
 
+/// Table of tracked LazySymbols.
+lazy_syms: LazySymbolTable = .{},
+
 /// Table of tracked Decls.
 decls: std.AutoArrayHashMapUnmanaged(Module.Decl.Index, DeclMetadata) = .{},
 
@@ -229,6 +232,18 @@ const is_hot_update_compatible = switch (builtin.target.os.tag) {
     else => false,
 };
 
+const LazySymbolTable = std.ArrayHashMapUnmanaged(
+    link.File.LazySymbol,
+    LazySymbolMetadata,
+    link.File.LazySymbol.Context,
+    true,
+);
+
+const LazySymbolMetadata = struct {
+    atom: Atom.Index,
+    section: u8,
+};
+
 const DeclMetadata = struct {
     atom: Atom.Index,
     section: u8,
@@ -497,6 +512,19 @@ pub fn flushModule(self: *MachO, comp: *Compilation, prog_node: *std.Progress.No
     sub_prog_node.activate();
     defer sub_prog_node.end();
 
+    {
+        var lazy_it = self.lazy_syms.iterator();
+        while (lazy_it.next()) |lazy_entry| {
+            self.updateLazySymbol(
+                lazy_entry.key_ptr.*,
+                lazy_entry.value_ptr.*,
+            ) catch |err| switch (err) {
+                error.CodegenFail => return error.FlushFailure,
+                else => |e| return e,
+            };
+        }
+    }
+
     const module = self.base.options.module orelse return error.LinkingWithoutZigSourceUnimplemented;
 
     if (self.d_sym) |*d_sym| {
@@ -2163,13 +2191,13 @@ pub fn lowerUnnamedConst(self: *MachO, typed_value: TypedValue, decl_index: Modu
 
     const name_str_index = blk: {
         const index = unnamed_consts.items.len;
-        const name = try std.fmt.allocPrint(gpa, "__unnamed_{s}_{d}", .{ decl_name, index });
+        const name = try std.fmt.allocPrint(gpa, "___unnamed_{s}_{d}", .{ decl_name, index });
         defer gpa.free(name);
         break :blk try self.strtab.insert(gpa, name);
     };
-    const name = self.strtab.get(name_str_index);
+    const name = self.strtab.get(name_str_index).?;
 
-    log.debug("allocating symbol indexes for {?s}", .{name});
+    log.debug("allocating symbol indexes for {s}", .{name});
 
     const atom_index = try self.createAtom();
 
@@ -2202,7 +2230,7 @@ pub fn lowerUnnamedConst(self: *MachO, typed_value: TypedValue, decl_index: Modu
 
     try unnamed_consts.append(gpa, atom_index);
 
-    log.debug("allocated atom for {?s} at 0x{x}", .{ name, symbol.n_value });
+    log.debug("allocated atom for {s} at 0x{x}", .{ name, symbol.n_value });
     log.debug("  (required alignment 0x{x})", .{required_alignment});
 
     try self.writeAtom(atom_index, code);
@@ -2282,6 +2310,100 @@ pub fn updateDecl(self: *MachO, module: *Module, decl_index: Module.Decl.Index)
     try self.updateDeclExports(module, decl_index, module.getDeclExports(decl_index));
 }
 
+fn updateLazySymbol(self: *MachO, lazy_sym: File.LazySymbol, lazy_metadata: LazySymbolMetadata) !void {
+    const gpa = self.base.allocator;
+    const mod = self.base.options.module.?;
+
+    var code_buffer = std.ArrayList(u8).init(gpa);
+    defer code_buffer.deinit();
+
+    const name_str_index = blk: {
+        const name = try std.fmt.allocPrint(gpa, "___lazy_{s}_{}", .{
+            @tagName(lazy_sym.kind),
+            lazy_sym.ty.fmt(mod),
+        });
+        defer gpa.free(name);
+        break :blk try self.strtab.insert(gpa, name);
+    };
+    const name = self.strtab.get(name_str_index).?;
+
+    const atom_index = lazy_metadata.atom;
+    const atom = self.getAtomPtr(atom_index);
+    const local_sym_index = atom.getSymbolIndex().?;
+
+    const src = if (lazy_sym.ty.getOwnerDeclOrNull()) |owner_decl|
+        mod.declPtr(owner_decl).srcLoc()
+    else
+        Module.SrcLoc{
+            .file_scope = undefined,
+            .parent_decl_node = undefined,
+            .lazy = .unneeded,
+        };
+    const res = try codegen.generateLazySymbol(
+        &self.base,
+        src,
+        lazy_sym,
+        &code_buffer,
+        .none,
+        .{ .parent_atom_index = local_sym_index },
+    );
+    const code = switch (res) {
+        .ok => code_buffer.items,
+        .fail => |em| {
+            log.err("{s}", .{em.msg});
+            return error.CodegenFail;
+        },
+    };
+
+    const required_alignment = atom.alignment;
+    const symbol = atom.getSymbolPtr(self);
+    symbol.n_strx = name_str_index;
+    symbol.n_type = macho.N_SECT;
+    symbol.n_sect = lazy_metadata.section + 1;
+    symbol.n_desc = 0;
+
+    const vaddr = try self.allocateAtom(atom_index, code.len, required_alignment);
+    errdefer self.freeAtom(atom_index);
+
+    log.debug("allocated atom for {s} at 0x{x}", .{ name, vaddr });
+    log.debug("  (required alignment 0x{x}", .{required_alignment});
+
+    atom.size = code.len;
+    symbol.n_value = vaddr;
+
+    const got_target = SymbolWithLoc{ .sym_index = local_sym_index, .file = null };
+    const got_index = try self.allocateGotEntry(got_target);
+    const got_atom_index = try self.createGotAtom(got_target);
+    const got_atom = self.getAtom(got_atom_index);
+    self.got_entries.items[got_index].sym_index = got_atom.getSymbolIndex().?;
+    try self.writePtrWidthAtom(got_atom_index);
+
+    self.markRelocsDirtyByTarget(atom.getSymbolWithLoc());
+    try self.writeAtom(atom_index, code);
+}
+
+pub fn getOrCreateAtomForLazySymbol(
+    self: *MachO,
+    lazy_sym: File.LazySymbol,
+    alignment: u32,
+) !Atom.Index {
+    const gop = try self.lazy_syms.getOrPutContext(self.base.allocator, lazy_sym, .{
+        .mod = self.base.options.module.?,
+    });
+    errdefer _ = self.lazy_syms.pop();
+    if (!gop.found_existing) {
+        gop.value_ptr.* = .{
+            .atom = try self.createAtom(),
+            .section = switch (lazy_sym.kind) {
+                .code => self.text_section_index.?,
+                .const_data => self.data_const_section_index.?,
+            },
+        };
+        self.getAtomPtr(gop.value_ptr.atom).alignment = alignment;
+    }
+    return gop.value_ptr.atom;
+}
+
 pub fn getOrCreateAtomForDecl(self: *MachO, decl_index: Module.Decl.Index) !Atom.Index {
     const gop = try self.decls.getOrPut(self.base.allocator, decl_index);
     if (!gop.found_existing) {