Merge pull request #15185 from ziglang/macho-tls

macho: add TLS support

5 files changed, 414 insertions, 397 deletions

diff --git a/src/link/Dwarf.zig b/src/link/Dwarf.zig
index 3fb6de7b73..0f2dfbda0e 100644
--- a/src/link/Dwarf.zig
+++ b/src/link/Dwarf.zig
@@ -150,7 +150,7 @@ pub const DeclState = struct {
                 .type = ty,
                 .offset = undefined,
             });
-            log.debug("%{d}: {}", .{ sym_index, ty.fmtDebug() });
+            log.debug("%{d}: {}", .{ sym_index, ty.fmt(self.mod) });
             try self.abbrev_resolver.putNoClobberContext(self.gpa, ty, sym_index, .{
                 .mod = self.mod,
             });
@@ -570,7 +570,7 @@ pub const DeclState = struct {
                 try dbg_info_buffer.append(0);
             },
             else => {
-                log.debug("TODO implement .debug_info for type '{}'", .{ty.fmtDebug()});
+                log.debug("TODO implement .debug_info for type '{}'", .{ty.fmt(self.mod)});
                 try dbg_info_buffer.append(@enumToInt(AbbrevKind.pad1));
             },
         }
@@ -1055,6 +1055,10 @@ pub fn commitDeclState(
                 },
             }
             {
+                log.debug("relocating subprogram high PC value: {x} => {x}", .{
+                    self.getRelocDbgInfoSubprogramHighPC(),
+                    sym_size,
+                });
                 const ptr = dbg_info_buffer.items[self.getRelocDbgInfoSubprogramHighPC()..][0..4];
                 mem.writeInt(u32, ptr, @intCast(u32, sym_size), target_endian);
             }
@@ -1263,7 +1267,12 @@ pub fn commitDeclState(
             } else {
                 const atom = self.getAtom(.di_atom, symbol.atom_index);
                 const value = atom.off + symbol.offset + reloc.addend;
-                log.debug("{x}: [() => {x}] (%{d}, '{}')", .{ reloc.offset, value, target, ty.fmtDebug() });
+                log.debug("{x}: [() => {x}] (%{d}, '{}')", .{
+                    reloc.offset,
+                    value,
+                    target,
+                    ty.fmt(module),
+                });
                 mem.writeInt(
                     u32,
                     dbg_info_buffer.items[reloc.offset..][0..@sizeOf(u32)],
diff --git a/src/link/MachO.zig b/src/link/MachO.zig
index e8fab08912..0ffb72f087 100644
--- a/src/link/MachO.zig
+++ b/src/link/MachO.zig
@@ -5,7 +5,6 @@ const build_options = @import("build_options");
 const builtin = @import("builtin");
 const assert = std.debug.assert;
 const dwarf = std.dwarf;
-const fmt = std.fmt;
 const fs = std.fs;
 const log = std.log.scoped(.link);
 const macho = std.macho;
@@ -138,6 +137,8 @@ got_section_index: ?u8 = null,
 data_const_section_index: ?u8 = null,
 la_symbol_ptr_section_index: ?u8 = null,
 data_section_index: ?u8 = null,
+thread_vars_section_index: ?u8 = null,
+thread_data_section_index: ?u8 = null,
 
 locals: std.ArrayListUnmanaged(macho.nlist_64) = .{},
 globals: std.ArrayListUnmanaged(SymbolWithLoc) = .{},
@@ -153,13 +154,9 @@ stub_helper_preamble_atom_index: ?Atom.Index = null,
 
 strtab: StringTable(.strtab) = .{},
 
-got_entries: std.ArrayListUnmanaged(Entry) = .{},
-got_entries_free_list: std.ArrayListUnmanaged(u32) = .{},
-got_entries_table: std.AutoHashMapUnmanaged(SymbolWithLoc, u32) = .{},
-
-stubs: std.ArrayListUnmanaged(Entry) = .{},
-stubs_free_list: std.ArrayListUnmanaged(u32) = .{},
-stubs_table: std.AutoHashMapUnmanaged(SymbolWithLoc, u32) = .{},
+got_table: SectionTable = .{},
+stubs_table: SectionTable = .{},
+tlv_table: SectionTable = .{},
 
 error_flags: File.ErrorFlags = File.ErrorFlags{},
 
@@ -268,26 +265,120 @@ const DeclMetadata = struct {
     }
 };
 
-const Entry = struct {
-    target: SymbolWithLoc,
-    // Index into the synthetic symbol table (i.e., file == null).
-    sym_index: u32,
+const SectionTable = struct {
+    entries: std.ArrayListUnmanaged(Entry) = .{},
+    free_list: std.ArrayListUnmanaged(u32) = .{},
+    lookup: std.AutoHashMapUnmanaged(SymbolWithLoc, u32) = .{},
+
+    pub fn deinit(st: *ST, allocator: Allocator) void {
+        st.entries.deinit(allocator);
+        st.free_list.deinit(allocator);
+        st.lookup.deinit(allocator);
+    }
+
+    pub fn allocateEntry(st: *ST, allocator: Allocator, target: SymbolWithLoc) !u32 {
+        try st.entries.ensureUnusedCapacity(allocator, 1);
+        const index = blk: {
+            if (st.free_list.popOrNull()) |index| {
+                log.debug("  (reusing entry index {d})", .{index});
+                break :blk index;
+            } else {
+                log.debug("  (allocating entry at index {d})", .{st.entries.items.len});
+                const index = @intCast(u32, st.entries.items.len);
+                _ = st.entries.addOneAssumeCapacity();
+                break :blk index;
+            }
+        };
+        st.entries.items[index] = .{ .target = target, .sym_index = 0 };
+        try st.lookup.putNoClobber(allocator, target, index);
+        return index;
+    }
+
+    pub fn freeEntry(st: *ST, allocator: Allocator, target: SymbolWithLoc) void {
+        const index = st.lookup.get(target) orelse return;
+        st.free_list.append(allocator, index) catch {};
+        st.entries.items[index] = .{
+            .target = .{ .sym_index = 0 },
+            .sym_index = 0,
+        };
+        _ = st.lookup.remove(target);
+    }
 
-    pub fn getSymbol(entry: Entry, macho_file: *MachO) macho.nlist_64 {
-        return macho_file.getSymbol(.{ .sym_index = entry.sym_index, .file = null });
+    pub fn getAtomIndex(st: *const ST, macho_file: *MachO, target: SymbolWithLoc) ?Atom.Index {
+        const index = st.lookup.get(target) orelse return null;
+        return st.entries.items[index].getAtomIndex(macho_file);
     }
 
-    pub fn getSymbolPtr(entry: Entry, macho_file: *MachO) *macho.nlist_64 {
-        return macho_file.getSymbolPtr(.{ .sym_index = entry.sym_index, .file = null });
+    const FormatContext = struct {
+        macho_file: *MachO,
+        st: *const ST,
+    };
+
+    fn fmt(
+        ctx: FormatContext,
+        comptime unused_format_string: []const u8,
+        options: std.fmt.FormatOptions,
+        writer: anytype,
+    ) @TypeOf(writer).Error!void {
+        _ = options;
+        comptime assert(unused_format_string.len == 0);
+        try writer.writeAll("SectionTable:\n");
+        for (ctx.st.entries.items, 0..) |entry, i| {
+            const atom_sym = entry.getSymbol(ctx.macho_file);
+            const target_sym = ctx.macho_file.getSymbol(entry.target);
+            try writer.print("  {d}@{x} => ", .{ i, atom_sym.n_value });
+            if (target_sym.undf()) {
+                try writer.print("import('{s}')", .{
+                    ctx.macho_file.getSymbolName(entry.target),
+                });
+            } else {
+                try writer.print("local(%{d}) in object({?d})", .{
+                    entry.target.sym_index,
+                    entry.target.file,
+                });
+            }
+            try writer.writeByte('\n');
+        }
     }
 
-    pub fn getAtomIndex(entry: Entry, macho_file: *MachO) ?Atom.Index {
-        return macho_file.getAtomIndexForSymbol(.{ .sym_index = entry.sym_index, .file = null });
+    fn format(st: *const ST, comptime unused_format_string: []const u8, options: std.fmt.FormatOptions, writer: anytype) !void {
+        _ = st;
+        _ = unused_format_string;
+        _ = options;
+        _ = writer;
+        @compileError("do not format SectionTable directly; use st.fmtDebug()");
     }
 
-    pub fn getName(entry: Entry, macho_file: *MachO) []const u8 {
-        return macho_file.getSymbolName(.{ .sym_index = entry.sym_index, .file = null });
+    pub fn fmtDebug(st: *const ST, macho_file: *MachO) std.fmt.Formatter(fmt) {
+        return .{ .data = .{
+            .macho_file = macho_file,
+            .st = st,
+        } };
     }
+
+    const ST = @This();
+
+    const Entry = struct {
+        target: SymbolWithLoc,
+        // Index into the synthetic symbol table (i.e., file == null).
+        sym_index: u32,
+
+        pub fn getSymbol(entry: Entry, macho_file: *MachO) macho.nlist_64 {
+            return macho_file.getSymbol(.{ .sym_index = entry.sym_index });
+        }
+
+        pub fn getSymbolPtr(entry: Entry, macho_file: *MachO) *macho.nlist_64 {
+            return macho_file.getSymbolPtr(.{ .sym_index = entry.sym_index });
+        }
+
+        pub fn getAtomIndex(entry: Entry, macho_file: *MachO) ?Atom.Index {
+            return macho_file.getAtomIndexForSymbol(.{ .sym_index = entry.sym_index });
+        }
+
+        pub fn getName(entry: Entry, macho_file: *MachO) []const u8 {
+            return macho_file.getSymbolName(.{ .sym_index = entry.sym_index });
+        }
+    };
 };
 
 const BindingTable = std.AutoArrayHashMapUnmanaged(Atom.Index, std.ArrayListUnmanaged(Atom.Binding));
@@ -397,7 +488,7 @@ pub fn openPath(allocator: Allocator, options: link.Options) !*MachO {
         // Create dSYM bundle.
         log.debug("creating {s}.dSYM bundle", .{sub_path});
 
-        const d_sym_path = try fmt.allocPrint(
+        const d_sym_path = try std.fmt.allocPrint(
             allocator,
             "{s}.dSYM" ++ fs.path.sep_str ++ "Contents" ++ fs.path.sep_str ++ "Resources" ++ fs.path.sep_str ++ "DWARF",
             .{sub_path},
@@ -611,6 +702,9 @@ pub fn flushModule(self: *MachO, comp: *Compilation, prog_node: *std.Progress.No
     if (self.dyld_stub_binder_index == null) {
         self.dyld_stub_binder_index = try self.addUndefined("dyld_stub_binder", .add_got);
     }
+    if (!self.base.options.single_threaded) {
+        _ = try self.addUndefined("__tlv_bootstrap", .none);
+    }
 
     try self.createMhExecuteHeaderSymbol();
 
@@ -619,6 +713,12 @@ pub fn flushModule(self: *MachO, comp: *Compilation, prog_node: *std.Progress.No
     try self.resolveSymbolsInDylibs(&actions);
 
     if (self.unresolved.count() > 0) {
+        for (self.unresolved.keys()) |index| {
+            // TODO: convert into compiler errors.
+            const global = self.globals.items[index];
+            const sym_name = self.getSymbolName(global);
+            log.err("undefined symbol reference '{s}'", .{sym_name});
+        }
         return error.UndefinedSymbolReference;
     }
 
@@ -1237,22 +1337,17 @@ pub fn createAtom(self: *MachO) !Atom.Index {
 
 pub fn createGotAtom(self: *MachO, target: SymbolWithLoc) !Atom.Index {
     const atom_index = try self.createAtom();
-    const atom = self.getAtomPtr(atom_index);
-    atom.size = @sizeOf(u64);
+    self.getAtomPtr(atom_index).size = @sizeOf(u64);
 
-    const sym = atom.getSymbolPtr(self);
+    const sym = self.getAtom(atom_index).getSymbolPtr(self);
     sym.n_type = macho.N_SECT;
     sym.n_sect = self.got_section_index.? + 1;
-    sym.n_value = try self.allocateAtom(atom_index, atom.size, @alignOf(u64));
+    sym.n_value = try self.allocateAtom(atom_index, @sizeOf(u64), @alignOf(u64));
 
     log.debug("allocated GOT atom at 0x{x}", .{sym.n_value});
 
     try Atom.addRelocation(self, atom_index, .{
-        .type = switch (self.base.options.target.cpu.arch) {
-            .aarch64 => @enumToInt(macho.reloc_type_arm64.ARM64_RELOC_UNSIGNED),
-            .x86_64 => @enumToInt(macho.reloc_type_x86_64.X86_64_RELOC_UNSIGNED),
-            else => unreachable,
-        },
+        .type = .unsigned,
         .target = target,
         .offset = 0,
         .addend = 0,
@@ -1269,6 +1364,7 @@ pub fn createGotAtom(self: *MachO, target: SymbolWithLoc) !Atom.Index {
     } else {
         try Atom.addRebase(self, atom_index, 0);
     }
+    try self.writePtrWidthAtom(atom_index);
 
     return atom_index;
 }
@@ -1334,15 +1430,15 @@ fn createStubHelperPreambleAtom(self: *MachO) !void {
             code[9] = 0xff;
             code[10] = 0x25;
 
-            try Atom.addRelocations(self, atom_index, 2, .{ .{
-                .type = @enumToInt(macho.reloc_type_x86_64.X86_64_RELOC_SIGNED),
+            try Atom.addRelocations(self, atom_index, &[_]Relocation{ .{
+                .type = .signed,
                 .target = dyld_private,
                 .offset = 3,
                 .addend = 0,
                 .pcrel = true,
                 .length = 2,
             }, .{
-                .type = @enumToInt(macho.reloc_type_x86_64.X86_64_RELOC_GOT),
+                .type = .got,
                 .target = dyld_stub_binder,
                 .offset = 11,
                 .addend = 0,
@@ -1374,29 +1470,29 @@ fn createStubHelperPreambleAtom(self: *MachO) !void {
             // br x16
             mem.writeIntLittle(u32, code[20..][0..4], aarch64.Instruction.br(.x16).toU32());
 
-            try Atom.addRelocations(self, atom_index, 4, .{ .{
-                .type = @enumToInt(macho.reloc_type_arm64.ARM64_RELOC_PAGE21),
+            try Atom.addRelocations(self, atom_index, &[_]Relocation{ .{
+                .type = .page,
                 .target = dyld_private,
                 .offset = 0,
                 .addend = 0,
                 .pcrel = true,
                 .length = 2,
             }, .{
-                .type = @enumToInt(macho.reloc_type_arm64.ARM64_RELOC_PAGEOFF12),
+                .type = .pageoff,
                 .target = dyld_private,
                 .offset = 4,
                 .addend = 0,
                 .pcrel = false,
                 .length = 2,
             }, .{
-                .type = @enumToInt(macho.reloc_type_arm64.ARM64_RELOC_GOT_LOAD_PAGE21),
+                .type = .got_page,
                 .target = dyld_stub_binder,
                 .offset = 12,
                 .addend = 0,
                 .pcrel = true,
                 .length = 2,
             }, .{
-                .type = @enumToInt(macho.reloc_type_arm64.ARM64_RELOC_GOT_LOAD_PAGEOFF12),
+                .type = .got_pageoff,
                 .target = dyld_stub_binder,
                 .offset = 16,
                 .addend = 0,
@@ -1454,8 +1550,8 @@ fn createStubHelperAtom(self: *MachO) !Atom.Index {
             code[5] = 0xe9;
 
             try Atom.addRelocation(self, atom_index, .{
-                .type = @enumToInt(macho.reloc_type_x86_64.X86_64_RELOC_BRANCH),
-                .target = .{ .sym_index = stub_helper_preamble_atom_sym_index, .file = null },
+                .type = .branch,
+                .target = .{ .sym_index = stub_helper_preamble_atom_sym_index },
                 .offset = 6,
                 .addend = 0,
                 .pcrel = true,
@@ -1477,8 +1573,8 @@ fn createStubHelperAtom(self: *MachO) !Atom.Index {
             // Next 4 bytes 8..12 are just a placeholder populated in `populateLazyBindOffsetsInStubHelper`.
 
             try Atom.addRelocation(self, atom_index, .{
-                .type = @enumToInt(macho.reloc_type_arm64.ARM64_RELOC_BRANCH26),
-                .target = .{ .sym_index = stub_helper_preamble_atom_sym_index, .file = null },
+                .type = .branch,
+                .target = .{ .sym_index = stub_helper_preamble_atom_sym_index },
                 .offset = 4,
                 .addend = 0,
                 .pcrel = true,
@@ -1505,12 +1601,8 @@ fn createLazyPointerAtom(self: *MachO, stub_sym_index: u32, target: SymbolWithLo
     sym.n_sect = self.la_symbol_ptr_section_index.? + 1;
 
     try Atom.addRelocation(self, atom_index, .{
-        .type = switch (self.base.options.target.cpu.arch) {
-            .aarch64 => @enumToInt(macho.reloc_type_arm64.ARM64_RELOC_UNSIGNED),
-            .x86_64 => @enumToInt(macho.reloc_type_x86_64.X86_64_RELOC_UNSIGNED),
-            else => unreachable,
-        },
-        .target = .{ .sym_index = stub_sym_index, .file = null },
+        .type = .unsigned,
+        .target = .{ .sym_index = stub_sym_index },
         .offset = 0,
         .addend = 0,
         .pcrel = false,
@@ -1563,8 +1655,8 @@ fn createStubAtom(self: *MachO, laptr_sym_index: u32) !Atom.Index {
             code[1] = 0x25;
 
             try Atom.addRelocation(self, atom_index, .{
-                .type = @enumToInt(macho.reloc_type_x86_64.X86_64_RELOC_BRANCH),
-                .target = .{ .sym_index = laptr_sym_index, .file = null },
+                .type = .branch,
+                .target = .{ .sym_index = laptr_sym_index },
                 .offset = 2,
                 .addend = 0,
                 .pcrel = true,
@@ -1583,18 +1675,18 @@ fn createStubAtom(self: *MachO, laptr_sym_index: u32) !Atom.Index {
             // br x16
             mem.writeIntLittle(u32, code[8..12], aarch64.Instruction.br(.x16).toU32());
 
-            try Atom.addRelocations(self, atom_index, 2, .{
+            try Atom.addRelocations(self, atom_index, &[_]Relocation{
                 .{
-                    .type = @enumToInt(macho.reloc_type_arm64.ARM64_RELOC_PAGE21),
-                    .target = .{ .sym_index = laptr_sym_index, .file = null },
+                    .type = .page,
+                    .target = .{ .sym_index = laptr_sym_index },
                     .offset = 0,
                     .addend = 0,
                     .pcrel = true,
                     .length = 2,
                 },
                 .{
-                    .type = @enumToInt(macho.reloc_type_arm64.ARM64_RELOC_PAGEOFF12),
-                    .target = .{ .sym_index = laptr_sym_index, .file = null },
+                    .type = .pageoff,
+                    .target = .{ .sym_index = laptr_sym_index },
                     .offset = 4,
                     .addend = 0,
                     .pcrel = false,
@@ -1612,6 +1704,42 @@ fn createStubAtom(self: *MachO, laptr_sym_index: u32) !Atom.Index {
     return atom_index;
 }
 
+fn createThreadLocalDescriptorAtom(self: *MachO, target: SymbolWithLoc) !Atom.Index {
+    const gpa = self.base.allocator;
+    const size = 3 * @sizeOf(u64);
+    const required_alignment: u32 = 1;
+    const atom_index = try self.createAtom();
+    self.getAtomPtr(atom_index).size = size;
+
+    const target_sym_name = self.getSymbolName(target);
+    const name_delimiter = mem.indexOf(u8, target_sym_name, "$").?;
+    const sym_name = try gpa.dupe(u8, target_sym_name[0..name_delimiter]);
+    defer gpa.free(sym_name);
+
+    const sym = self.getAtom(atom_index).getSymbolPtr(self);
+    sym.n_type = macho.N_SECT;
+    sym.n_sect = self.thread_vars_section_index.? + 1;
+    sym.n_strx = try self.strtab.insert(gpa, sym_name);
+    sym.n_value = try self.allocateAtom(atom_index, size, required_alignment);
+
+    log.debug("allocated threadlocal descriptor atom '{s}' at 0x{x}", .{ sym_name, sym.n_value });
+
+    try Atom.addRelocation(self, atom_index, .{
+        .type = .tlv_initializer,
+        .target = target,
+        .offset = 0x10,
+        .addend = 0,
+        .pcrel = false,
+        .length = 3,
+    });
+
+    var code: [size]u8 = undefined;
+    mem.set(u8, &code, 0);
+    try self.writeAtom(atom_index, &code);
+
+    return atom_index;
+}
+
 fn createMhExecuteHeaderSymbol(self: *MachO) !void {
     if (self.base.options.output_mode != .Exe) return;
     if (self.getGlobal("__mh_execute_header")) |global| {
@@ -1760,12 +1888,9 @@ pub fn deinit(self: *MachO) void {
         d_sym.deinit();
     }
 
-    self.got_entries.deinit(gpa);
-    self.got_entries_free_list.deinit(gpa);
-    self.got_entries_table.deinit(gpa);
-    self.stubs.deinit(gpa);
-    self.stubs_free_list.deinit(gpa);
+    self.got_table.deinit(gpa);
     self.stubs_table.deinit(gpa);
+    self.tlv_table.deinit(gpa);
     self.strtab.deinit(gpa);
 
     self.locals.deinit(gpa);
@@ -1898,20 +2023,10 @@ fn freeAtom(self: *MachO, atom_index: Atom.Index) void {
     self.locals_free_list.append(gpa, sym_index) catch {};
 
     // Try freeing GOT atom if this decl had one
-    const got_target = SymbolWithLoc{ .sym_index = sym_index, .file = null };
-    if (self.got_entries_table.get(got_target)) |got_index| {
-        self.got_entries_free_list.append(gpa, @intCast(u32, got_index)) catch {};
-        self.got_entries.items[got_index] = .{
-            .target = .{ .sym_index = 0, .file = null },
-            .sym_index = 0,
-        };
-        _ = self.got_entries_table.remove(got_target);
-
-        if (self.d_sym) |*d_sym| {
-            d_sym.swapRemoveRelocs(sym_index);
-        }
+    self.got_table.freeEntry(gpa, .{ .sym_index = sym_index });
 
-        log.debug("  adding GOT index {d} to free list (target local@{d})", .{ got_index, sym_index });
+    if (self.d_sym) |*d_sym| {
+        d_sym.swapRemoveRelocs(sym_index);
     }
 
     self.locals.items[sym_index].n_type = 0;
@@ -1986,70 +2101,34 @@ fn allocateGlobal(self: *MachO) !u32 {
     return index;
 }
 
-fn allocateGotEntry(self: *MachO, target: SymbolWithLoc) !u32 {
-    const gpa = self.base.allocator;
-    try self.got_entries.ensureUnusedCapacity(gpa, 1);
-
-    const index = blk: {
-        if (self.got_entries_free_list.popOrNull()) |index| {
-            log.debug("  (reusing GOT entry index {d})", .{index});
-            break :blk index;
-        } else {
-            log.debug("  (allocating GOT entry at index {d})", .{self.got_entries.items.len});
-            const index = @intCast(u32, self.got_entries.items.len);
-            _ = self.got_entries.addOneAssumeCapacity();
-            break :blk index;
-        }
-    };
-
-    self.got_entries.items[index] = .{ .target = target, .sym_index = 0 };
-    try self.got_entries_table.putNoClobber(gpa, target, index);
-
-    return index;
-}
-
 fn addGotEntry(self: *MachO, target: SymbolWithLoc) !void {
-    if (self.got_entries_table.contains(target)) return;
-
-    const got_index = try self.allocateGotEntry(target);
+    if (self.got_table.lookup.contains(target)) return;
+    const got_index = try self.got_table.allocateEntry(self.base.allocator, target);
     const got_atom_index = try self.createGotAtom(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);
-}
-
-fn allocateStubEntry(self: *MachO, target: SymbolWithLoc) !u32 {
-    try self.stubs.ensureUnusedCapacity(self.base.allocator, 1);
-
-    const index = blk: {
-        if (self.stubs_free_list.popOrNull()) |index| {
-            log.debug("  (reusing stub entry index {d})", .{index});
-            break :blk index;
-        } else {
-            log.debug("  (allocating stub entry at index {d})", .{self.stubs.items.len});
-            const index = @intCast(u32, self.stubs.items.len);
-            _ = self.stubs.addOneAssumeCapacity();
-            break :blk index;
-        }
-    };
-
-    self.stubs.items[index] = .{ .target = target, .sym_index = 0 };
-    try self.stubs_table.putNoClobber(self.base.allocator, target, index);
-
-    return index;
+    self.got_table.entries.items[got_index].sym_index = got_atom.getSymbolIndex().?;
+    self.markRelocsDirtyByTarget(target);
 }
 
 fn addStubEntry(self: *MachO, target: SymbolWithLoc) !void {
-    if (self.stubs_table.contains(target)) return;
-
-    const stub_index = try self.allocateStubEntry(target);
+    if (self.stubs_table.lookup.contains(target)) return;
+    const stub_index = try self.stubs_table.allocateEntry(self.base.allocator, target);
     const stub_helper_atom_index = try self.createStubHelperAtom();
     const stub_helper_atom = self.getAtom(stub_helper_atom_index);
     const laptr_atom_index = try self.createLazyPointerAtom(stub_helper_atom.getSymbolIndex().?, target);
     const laptr_atom = self.getAtom(laptr_atom_index);
     const stub_atom_index = try self.createStubAtom(laptr_atom.getSymbolIndex().?);
     const stub_atom = self.getAtom(stub_atom_index);
-    self.stubs.items[stub_index].sym_index = stub_atom.getSymbolIndex().?;
+    self.stubs_table.entries.items[stub_index].sym_index = stub_atom.getSymbolIndex().?;
+    self.markRelocsDirtyByTarget(target);
+}
+
+fn addTlvEntry(self: *MachO, target: SymbolWithLoc) !void {
+    if (self.tlv_table.lookup.contains(target)) return;
+    const tlv_index = try self.tlv_table.allocateEntry(self.base.allocator, target);
+    const tlv_atom_index = try self.createThreadLocalDescriptorAtom(target);
+    const tlv_atom = self.getAtom(tlv_atom_index);
+    self.tlv_table.entries.items[tlv_index].sym_index = tlv_atom.getSymbolIndex().?;
     self.markRelocsDirtyByTarget(target);
 }
 
@@ -2070,8 +2149,6 @@ pub fn updateFunc(self: *MachO, module: *Module, func: *Module.Fn, air: Air, liv
     self.freeUnnamedConsts(decl_index);
     Atom.freeRelocations(self, atom_index);
 
-    const atom = self.getAtom(atom_index);
-
     var code_buffer = std.ArrayList(u8).init(self.base.allocator);
     defer code_buffer.deinit();
 
@@ -2100,7 +2177,13 @@ pub fn updateFunc(self: *MachO, module: *Module, func: *Module.Fn, air: Air, liv
     const addr = try self.updateDeclCode(decl_index, code);
 
     if (decl_state) |*ds| {
-        try self.d_sym.?.dwarf.commitDeclState(module, decl_index, addr, atom.size, ds);
+        try self.d_sym.?.dwarf.commitDeclState(
+            module,
+            decl_index,
+            addr,
+            self.getAtom(atom_index).size,
+            ds,
+        );
     }
 
     // Since we updated the vaddr and the size, each corresponding export symbol also
@@ -2196,8 +2279,8 @@ pub fn updateDecl(self: *MachO, module: *Module, decl_index: Module.Decl.Index)
     }
 
     const atom_index = try self.getOrCreateAtomForDecl(decl_index);
+    const sym_index = self.getAtom(atom_index).getSymbolIndex().?;
     Atom.freeRelocations(self, atom_index);
-    const atom = self.getAtom(atom_index);
 
     var code_buffer = std.ArrayList(u8).init(self.base.allocator);
     defer code_buffer.deinit();
@@ -2216,14 +2299,14 @@ pub fn updateDecl(self: *MachO, module: *Module, decl_index: Module.Decl.Index)
         }, &code_buffer, .{
             .dwarf = ds,
         }, .{
-            .parent_atom_index = atom.getSymbolIndex().?,
+            .parent_atom_index = sym_index,
         })
     else
         try codegen.generateSymbol(&self.base, decl.srcLoc(), .{
             .ty = decl.ty,
             .val = decl_val,
         }, &code_buffer, .none, .{
-            .parent_atom_index = atom.getSymbolIndex().?,
+            .parent_atom_index = sym_index,
         });
 
     var code = switch (res) {
@@ -2237,7 +2320,13 @@ pub fn updateDecl(self: *MachO, module: *Module, decl_index: Module.Decl.Index)
     const addr = try self.updateDeclCode(decl_index, code);
 
     if (decl_state) |*ds| {
-        try self.d_sym.?.dwarf.commitDeclState(module, decl_index, addr, atom.size, ds);
+        try self.d_sym.?.dwarf.commitDeclState(
+            module,
+            decl_index,
+            addr,
+            self.getAtom(atom_index).size,
+            ds,
+        );
     }
 
     // Since we updated the vaddr and the size, each corresponding export symbol also
@@ -2322,7 +2411,6 @@ fn updateLazySymbolAtom(
     symbol.n_value = vaddr;
 
     try self.addGotEntry(.{ .sym_index = local_sym_index });
-    self.markRelocsDirtyByTarget(atom.getSymbolWithLoc());
     try self.writeAtom(atom_index, code);
 }
 
@@ -2356,6 +2444,7 @@ fn getDeclOutputSection(self: *MachO, decl_index: Module.Decl.Index) u8 {
     const val = decl.val;
     const zig_ty = ty.zigTypeTag();
     const mode = self.base.options.optimize_mode;
+    const single_threaded = self.base.options.single_threaded;
     const sect_id: u8 = blk: {
         // TODO finish and audit this function
         if (val.isUndefDeep()) {
@@ -2366,7 +2455,10 @@ fn getDeclOutputSection(self: *MachO, decl_index: Module.Decl.Index) u8 {
             }
         }
 
-        if (val.castTag(.variable)) |_| {
+        if (val.castTag(.variable)) |variable| {
+            if (variable.data.is_threadlocal and !single_threaded) {
+                break :blk self.thread_data_section_index.?;
+            }
             break :blk self.data_section_index.?;
         }
 
@@ -2391,16 +2483,28 @@ fn updateDeclCode(self: *MachO, decl_index: Module.Decl.Index, code: []u8) !u64
 
     const required_alignment = decl.getAlignment(self.base.options.target);
 
-    const sym_name = try decl.getFullyQualifiedName(mod);
-    defer self.base.allocator.free(sym_name);
+    const decl_name = try decl.getFullyQualifiedName(mod);
+    defer gpa.free(decl_name);
 
     const decl_metadata = self.decls.get(decl_index).?;
     const atom_index = decl_metadata.atom;
     const atom = self.getAtom(atom_index);
     const sym_index = atom.getSymbolIndex().?;
     const sect_id = decl_metadata.section;
+    const header = &self.sections.items(.header)[sect_id];
+    const segment = self.getSegment(sect_id);
+    const is_threadlocal = if (!self.base.options.single_threaded)
+        header.flags == macho.S_THREAD_LOCAL_REGULAR or header.flags == macho.S_THREAD_LOCAL_ZEROFILL
+    else
+        false;
     const code_len = code.len;
 
+    const sym_name = if (is_threadlocal)
+        try std.fmt.allocPrint(gpa, "{s}$tlv$init", .{decl_name})
+    else
+        decl_name;
+    defer if (is_threadlocal) gpa.free(sym_name);
+
     if (atom.size != 0) {
         const sym = atom.getSymbolPtr(self);
         sym.n_strx = try self.strtab.insert(gpa, sym_name);
@@ -2418,25 +2522,29 @@ fn updateDeclCode(self: *MachO, decl_index: Module.Decl.Index, code: []u8) !u64
 
             if (vaddr != sym.n_value) {
                 sym.n_value = vaddr;
+                // TODO: I think we should update the offset to the initializer here too.
+                const target: SymbolWithLoc = if (is_threadlocal) blk: {
+                    const tlv_atom_index = self.tlv_table.getAtomIndex(self, .{
+                        .sym_index = sym_index,
+                    }).?;
+                    const tlv_atom = self.getAtom(tlv_atom_index);
+                    break :blk tlv_atom.getSymbolWithLoc();
+                } else .{ .sym_index = sym_index };
+                self.markRelocsDirtyByTarget(target);
                 log.debug("  (updating GOT entry)", .{});
-                const got_target = SymbolWithLoc{ .sym_index = sym_index, .file = null };
-                const got_atom_index = self.getGotAtomIndexForSymbol(got_target).?;
-                self.markRelocsDirtyByTarget(got_target);
+                const got_atom_index = self.got_table.getAtomIndex(self, target).?;
                 try self.writePtrWidthAtom(got_atom_index);
             }
         } else if (code_len < atom.size) {
             self.shrinkAtom(atom_index, code_len);
         } else if (atom.next_index == null) {
-            const header = &self.sections.items(.header)[sect_id];
-            const segment = self.getSegment(sect_id);
             const needed_size = (sym.n_value + code_len) - segment.vmaddr;
             header.size = needed_size;
         }
         self.getAtomPtr(atom_index).size = code_len;
     } else {
-        const name_str_index = try self.strtab.insert(gpa, sym_name);
         const sym = atom.getSymbolPtr(self);
-        sym.n_strx = name_str_index;
+        sym.n_strx = try self.strtab.insert(gpa, sym_name);
         sym.n_type = macho.N_SECT;
         sym.n_sect = sect_id + 1;
         sym.n_desc = 0;
@@ -2450,10 +2558,17 @@ fn updateDeclCode(self: *MachO, decl_index: Module.Decl.Index, code: []u8) !u64
         self.getAtomPtr(atom_index).size = code_len;
         sym.n_value = vaddr;
 
-        try self.addGotEntry(.{ .sym_index = sym_index });
+        if (is_threadlocal) {
+            try self.addTlvEntry(.{ .sym_index = sym_index });
+        }
+        const target: SymbolWithLoc = if (is_threadlocal) blk: {
+            const tlv_atom_index = self.tlv_table.getAtomIndex(self, .{ .sym_index = sym_index }).?;
+            const tlv_atom = self.getAtom(tlv_atom_index);
+            break :blk tlv_atom.getSymbolWithLoc();
+        } else .{ .sym_index = sym_index };
+        try self.addGotEntry(target);
     }
 
-    self.markRelocsDirtyByTarget(atom.getSymbolWithLoc());
     try self.writeAtom(atom_index, code);
 
     return atom.getSymbol(self).n_value;
@@ -2647,11 +2762,7 @@ pub fn getDeclVAddr(self: *MachO, decl_index: Module.Decl.Index, reloc_info: Fil
     const sym_index = self.getAtom(this_atom_index).getSymbolIndex().?;
     const atom_index = self.getAtomIndexForSymbol(.{ .sym_index = reloc_info.parent_atom_index, .file = null }).?;
     try Atom.addRelocation(self, atom_index, .{
-        .type = switch (self.base.options.target.cpu.arch) {
-            .aarch64 => @enumToInt(macho.reloc_type_arm64.ARM64_RELOC_UNSIGNED),
-            .x86_64 => @enumToInt(macho.reloc_type_x86_64.X86_64_RELOC_UNSIGNED),
-            else => unreachable,
-        },
+        .type = .unsigned,
         .target = .{ .sym_index = sym_index, .file = null },
         .offset = @intCast(u32, reloc_info.offset),
         .addend = reloc_info.addend,
@@ -2790,6 +2901,28 @@ fn populateMissingMetadata(self: *MachO) !void {
         self.segment_table_dirty = true;
     }
 
+    if (!self.base.options.single_threaded) {
+        if (self.thread_vars_section_index == null) {
+            self.thread_vars_section_index = try self.allocateSection("__DATA2", "__thread_vars", .{
+                .size = @sizeOf(u64) * 3,
+                .alignment = @sizeOf(u64),
+                .flags = macho.S_THREAD_LOCAL_VARIABLES,
+                .prot = macho.PROT.READ | macho.PROT.WRITE,
+            });
+            self.segment_table_dirty = true;
+        }
+
+        if (self.thread_data_section_index == null) {
+            self.thread_data_section_index = try self.allocateSection("__DATA3", "__thread_data", .{
+                .size = @sizeOf(u64),
+                .alignment = @alignOf(u64),
+                .flags = macho.S_THREAD_LOCAL_REGULAR,
+                .prot = macho.PROT.READ | macho.PROT.WRITE,
+            });
+            self.segment_table_dirty = true;
+        }
+    }
+
     if (self.linkedit_segment_cmd_index == null) {
         self.linkedit_segment_cmd_index = @intCast(u8, self.segments.items.len);
 
@@ -3077,28 +3210,6 @@ fn allocateAtom(self: *MachO, atom_index: Atom.Index, new_atom_size: u64, alignm
     return vaddr;
 }
 
-fn getSectionPrecedence(header: macho.section_64) u4 {
-    if (header.isCode()) {
-        if (mem.eql(u8, "__text", header.sectName())) return 0x0;
-        if (header.type() == macho.S_SYMBOL_STUBS) return 0x1;
-        return 0x2;
-    }
-    switch (header.type()) {
-        macho.S_NON_LAZY_SYMBOL_POINTERS,
-        macho.S_LAZY_SYMBOL_POINTERS,
-        => return 0x0,
-        macho.S_MOD_INIT_FUNC_POINTERS => return 0x1,
-        macho.S_MOD_TERM_FUNC_POINTERS => return 0x2,
-        macho.S_ZEROFILL => return 0xf,
-        macho.S_THREAD_LOCAL_REGULAR => return 0xd,
-        macho.S_THREAD_LOCAL_ZEROFILL => return 0xe,
-        else => if (mem.eql(u8, "__eh_frame", header.sectName()))
-            return 0xf
-        else
-            return 0x3,
-    }
-}
-
 pub fn getGlobalSymbol(self: *MachO, name: []const u8, lib_name: ?[]const u8) !u32 {
     _ = lib_name;
     const gpa = self.base.allocator;
@@ -3474,8 +3585,8 @@ const SymtabCtx = struct {
 
 fn writeDysymtab(self: *MachO, ctx: SymtabCtx) !void {
     const gpa = self.base.allocator;
-    const nstubs = @intCast(u32, self.stubs_table.count());
-    const ngot_entries = @intCast(u32, self.got_entries_table.count());
+    const nstubs = @intCast(u32, self.stubs_table.lookup.count());
+    const ngot_entries = @intCast(u32, self.got_table.lookup.count());
     const nindirectsyms = nstubs * 2 + ngot_entries;
     const iextdefsym = ctx.nlocalsym;
     const iundefsym = iextdefsym + ctx.nextdefsym;
@@ -3497,7 +3608,7 @@ fn writeDysymtab(self: *MachO, ctx: SymtabCtx) !void {
     if (self.stubs_section_index) |sect_id| {
         const stubs = &self.sections.items(.header)[sect_id];
         stubs.reserved1 = 0;
-        for (self.stubs.items) |entry| {
+        for (self.stubs_table.entries.items) |entry| {
             if (entry.sym_index == 0) continue;
             const target_sym = self.getSymbol(entry.target);
             assert(target_sym.undf());
@@ -3508,7 +3619,7 @@ fn writeDysymtab(self: *MachO, ctx: SymtabCtx) !void {
     if (self.got_section_index) |sect_id| {
         const got = &self.sections.items(.header)[sect_id];
         got.reserved1 = nstubs;
-        for (self.got_entries.items) |entry| {
+        for (self.got_table.entries.items) |entry| {
             if (entry.sym_index == 0) continue;
             const target_sym = self.getSymbol(entry.target);
             if (target_sym.undf()) {
@@ -3522,7 +3633,7 @@ fn writeDysymtab(self: *MachO, ctx: SymtabCtx) !void {
     if (self.la_symbol_ptr_section_index) |sect_id| {
         const la_symbol_ptr = &self.sections.items(.header)[sect_id];
         la_symbol_ptr.reserved1 = nstubs + ngot_entries;
-        for (self.stubs.items) |entry| {
+        for (self.stubs_table.entries.items) |entry| {
             if (entry.sym_index == 0) continue;
             const target_sym = self.getSymbol(entry.target);
             assert(target_sym.undf());
@@ -3593,6 +3704,10 @@ fn writeHeader(self: *MachO, ncmds: u32, sizeofcmds: u32) !void {
     var header: macho.mach_header_64 = .{};
     header.flags = macho.MH_NOUNDEFS | macho.MH_DYLDLINK | macho.MH_PIE | macho.MH_TWOLEVEL;
 
+    if (!self.base.options.single_threaded) {
+        header.flags |= macho.MH_HAS_TLV_DESCRIPTORS;
+    }
+
     switch (self.base.options.target.cpu.arch) {
         .aarch64 => {
             header.cputype = macho.CPU_TYPE_ARM64;
@@ -3617,12 +3732,6 @@ fn writeHeader(self: *MachO, ncmds: u32, sizeofcmds: u32) !void {
         else => unreachable,
     }
 
-    if (self.getSectionByName("__DATA", "__thread_vars")) |sect_id| {
-        if (self.sections.items(.header)[sect_id].size > 0) {
-            header.flags |= macho.MH_HAS_TLV_DESCRIPTORS;
-        }
-    }
-
     header.ncmds = ncmds;
     header.sizeofcmds = sizeofcmds;
 
@@ -3802,8 +3911,7 @@ pub fn getSymbol(self: *const MachO, sym_with_loc: SymbolWithLoc) macho.nlist_64
 
 /// Returns name of the symbol described by `sym_with_loc` descriptor.
 pub fn getSymbolName(self: *const MachO, sym_with_loc: SymbolWithLoc) []const u8 {
-    assert(sym_with_loc.file == null);
-    const sym = self.locals.items[sym_with_loc.sym_index];
+    const sym = self.getSymbol(sym_with_loc);
     return self.strtab.get(sym.n_strx).?;
 }
 
@@ -3867,20 +3975,6 @@ pub fn getAtomIndexForSymbol(self: *MachO, sym_with_loc: SymbolWithLoc) ?Atom.In
     return self.atom_by_index_table.get(sym_with_loc.sym_index);
 }
 
-/// Returns GOT atom that references `sym_with_loc` if one exists.
-/// Returns null otherwise.
-pub fn getGotAtomIndexForSymbol(self: *MachO, sym_with_loc: SymbolWithLoc) ?Atom.Index {
-    const got_index = self.got_entries_table.get(sym_with_loc) orelse return null;
-    return self.got_entries.items[got_index].getAtomIndex(self);
-}
-
-/// Returns stubs atom that references `sym_with_loc` if one exists.
-/// Returns null otherwise.
-pub fn getStubsAtomIndexForSymbol(self: *MachO, sym_with_loc: SymbolWithLoc) ?Atom.Index {
-    const stubs_index = self.stubs_table.get(sym_with_loc) orelse return null;
-    return self.stubs.items[stubs_index].getAtomIndex(self);
-}
-
 /// Returns symbol location corresponding to the set entrypoint.
 /// Asserts output mode is executable.
 pub fn getEntryPoint(self: MachO) error{MissingMainEntrypoint}!SymbolWithLoc {
@@ -4227,37 +4321,13 @@ pub fn logSymtab(self: *MachO) void {
     }
 
     log.debug("GOT entries:", .{});
-    for (self.got_entries.items, 0..) |entry, i| {
-        const atom_sym = entry.getSymbol(self);
-        const target_sym = self.getSymbol(entry.target);
-        if (target_sym.undf()) {
-            log.debug("  {d}@{x} => import('{s}')", .{
-                i,
-                atom_sym.n_value,
-                self.getSymbolName(entry.target),
-            });
-        } else {
-            log.debug("  {d}@{x} => local(%{d}) in object({?d}) {s}", .{
-                i,
-                atom_sym.n_value,
-                entry.target.sym_index,
-                entry.target.file,
-                logSymAttributes(target_sym, &buf),
-            });
-        }
-    }
+    log.debug("{}", .{self.got_table.fmtDebug(self)});
 
     log.debug("stubs entries:", .{});
-    for (self.stubs.items, 0..) |entry, i| {
-        const target_sym = self.getSymbol(entry.target);
-        const atom_sym = entry.getSymbol(self);
-        assert(target_sym.undf());
-        log.debug("  {d}@{x} => import('{s}')", .{
-            i,
-            atom_sym.n_value,
-            self.getSymbolName(entry.target),
-        });
-    }
+    log.debug("{}", .{self.stubs_table.fmtDebug(self)});
+
+    log.debug("threadlocal entries:", .{});
+    log.debug("{}", .{self.tlv_table.fmtDebug(self)});
 }
 
 pub fn logAtoms(self: *MachO) void {
diff --git a/src/link/MachO/Atom.zig b/src/link/MachO/Atom.zig
index bd1a21a04f..5b17dc689d 100644
--- a/src/link/MachO/Atom.zig
+++ b/src/link/MachO/Atom.zig
@@ -14,7 +14,7 @@ const trace = @import("../../tracy.zig").trace;
 const Allocator = mem.Allocator;
 const Arch = std.Target.Cpu.Arch;
 const MachO = @import("../MachO.zig");
-const Relocation = @import("Relocation.zig");
+pub const Relocation = @import("Relocation.zig");
 const SymbolWithLoc = MachO.SymbolWithLoc;
 
 /// Each decl always gets a local symbol with the fully qualified name.
@@ -113,25 +113,19 @@ pub fn freeListEligible(self: Atom, macho_file: *MachO) bool {
 }
 
 pub fn addRelocation(macho_file: *MachO, atom_index: Index, reloc: Relocation) !void {
-    return addRelocations(macho_file, atom_index, 1, .{reloc});
+    return addRelocations(macho_file, atom_index, &[_]Relocation{reloc});
 }
 
-pub fn addRelocations(
-    macho_file: *MachO,
-    atom_index: Index,
-    comptime count: comptime_int,
-    relocs: [count]Relocation,
-) !void {
+pub fn addRelocations(macho_file: *MachO, atom_index: Index, relocs: []Relocation) !void {
     const gpa = macho_file.base.allocator;
-    const target = macho_file.base.options.target;
     const gop = try macho_file.relocs.getOrPut(gpa, atom_index);
     if (!gop.found_existing) {
         gop.value_ptr.* = .{};
     }
-    try gop.value_ptr.ensureUnusedCapacity(gpa, count);
+    try gop.value_ptr.ensureUnusedCapacity(gpa, relocs.len);
     for (relocs) |reloc| {
         log.debug("  (adding reloc of type {s} to target %{d})", .{
-            reloc.fmtType(target),
+            @tagName(reloc.type),
             reloc.target.sym_index,
         });
         gop.value_ptr.appendAssumeCapacity(reloc);
diff --git a/src/link/MachO/DebugSymbols.zig b/src/link/MachO/DebugSymbols.zig
index 1f41fc1cb8..98abf2b1cc 100644
--- a/src/link/MachO/DebugSymbols.zig
+++ b/src/link/MachO/DebugSymbols.zig
@@ -226,26 +226,20 @@ pub fn flushModule(self: *DebugSymbols, macho_file: *MachO) !void {
 
     for (self.relocs.items) |*reloc| {
         const sym = switch (reloc.type) {
-            .direct_load => macho_file.getSymbol(.{ .sym_index = reloc.target, .file = null }),
+            .direct_load => macho_file.getSymbol(.{ .sym_index = reloc.target }),
             .got_load => blk: {
-                const got_index = macho_file.got_entries_table.get(.{
-                    .sym_index = reloc.target,
-                    .file = null,
-                }).?;
-                const got_entry = macho_file.got_entries.items[got_index];
+                const got_index = macho_file.got_table.lookup.get(.{ .sym_index = reloc.target }).?;
+                const got_entry = macho_file.got_table.entries.items[got_index];
                 break :blk got_entry.getSymbol(macho_file);
             },
         };
         if (sym.n_value == reloc.prev_vaddr) continue;
 
         const sym_name = switch (reloc.type) {
-            .direct_load => macho_file.getSymbolName(.{ .sym_index = reloc.target, .file = null }),
+            .direct_load => macho_file.getSymbolName(.{ .sym_index = reloc.target }),
             .got_load => blk: {
-                const got_index = macho_file.got_entries_table.get(.{
-                    .sym_index = reloc.target,
-                    .file = null,
-                }).?;
-                const got_entry = macho_file.got_entries.items[got_index];
+                const got_index = macho_file.got_table.lookup.get(.{ .sym_index = reloc.target }).?;
+                const got_entry = macho_file.got_table.entries.items[got_index];
                 break :blk got_entry.getName(macho_file);
             },
         };
diff --git a/src/link/MachO/Relocation.zig b/src/link/MachO/Relocation.zig
index 32f24f243d..81340b1120 100644
--- a/src/link/MachO/Relocation.zig
+++ b/src/link/MachO/Relocation.zig
@@ -1,19 +1,7 @@
-const Relocation = @This();
+//! Relocation used by the self-hosted backends to instruct the linker where and how to
+//! fixup the values when flushing the contents to file and/or memory.
 
-const std = @import("std");
-const aarch64 = @import("../../arch/aarch64/bits.zig");
-const assert = std.debug.assert;
-const log = std.log.scoped(.link);
-const macho = std.macho;
-const math = std.math;
-const mem = std.mem;
-const meta = std.meta;
-
-const Atom = @import("Atom.zig");
-const MachO = @import("../MachO.zig");
-const SymbolWithLoc = MachO.SymbolWithLoc;
-
-type: u4,
+type: Type,
 target: SymbolWithLoc,
 offset: u32,
 addend: i64,
@@ -21,39 +9,55 @@ pcrel: bool,
 length: u2,
 dirty: bool = true,
 
+pub const Type = enum {
+    // x86, x86_64
+    /// RIP-relative displacement to a GOT pointer
+    got,
+    /// RIP-relative displacement
+    signed,
+    /// RIP-relative displacement to GOT pointer to TLV thunk
+    tlv,
+
+    // aarch64
+    /// PC-relative distance to target page in GOT section
+    got_page,
+    /// Offset to a GOT pointer relative to the start of a page in GOT section
+    got_pageoff,
+    /// PC-relative distance to target page in a section
+    page,
+    /// Offset to a pointer relative to the start of a page in a section
+    pageoff,
+
+    // common
+    /// PC/RIP-relative displacement B/BL/CALL
+    branch,
+    /// Absolute pointer value
+    unsigned,
+    /// Relative offset to TLV initializer
+    tlv_initializer,
+};
+
 /// Returns true if and only if the reloc is dirty AND the target address is available.
 pub fn isResolvable(self: Relocation, macho_file: *MachO) bool {
     _ = self.getTargetAtomIndex(macho_file) orelse return false;
     return self.dirty;
 }
 
-pub fn fmtType(self: Relocation, target: std.Target) []const u8 {
-    switch (target.cpu.arch) {
-        .aarch64 => return @tagName(@intToEnum(macho.reloc_type_arm64, self.type)),
-        .x86_64 => return @tagName(@intToEnum(macho.reloc_type_x86_64, self.type)),
-        else => unreachable,
-    }
-}
-
 pub fn getTargetAtomIndex(self: Relocation, macho_file: *MachO) ?Atom.Index {
-    switch (macho_file.base.options.target.cpu.arch) {
-        .aarch64 => switch (@intToEnum(macho.reloc_type_arm64, self.type)) {
-            .ARM64_RELOC_GOT_LOAD_PAGE21,
-            .ARM64_RELOC_GOT_LOAD_PAGEOFF12,
-            .ARM64_RELOC_POINTER_TO_GOT,
-            => return macho_file.getGotAtomIndexForSymbol(self.target),
-            else => {},
+    return switch (self.type) {
+        .got, .got_page, .got_pageoff => macho_file.got_table.getAtomIndex(macho_file, self.target),
+        .tlv => {
+            const thunk_atom_index = macho_file.tlv_table.getAtomIndex(macho_file, self.target) orelse
+                return null;
+            const thunk_atom = macho_file.getAtom(thunk_atom_index);
+            return macho_file.got_table.getAtomIndex(macho_file, thunk_atom.getSymbolWithLoc());
         },
-        .x86_64 => switch (@intToEnum(macho.reloc_type_x86_64, self.type)) {
-            .X86_64_RELOC_GOT,
-            .X86_64_RELOC_GOT_LOAD,
-            => return macho_file.getGotAtomIndexForSymbol(self.target),
-            else => {},
-        },
-        else => unreachable,
-    }
-    if (macho_file.getStubsAtomIndexForSymbol(self.target)) |stubs_atom| return stubs_atom;
-    return macho_file.getAtomIndexForSymbol(self.target);
+        .branch => if (macho_file.stubs_table.getAtomIndex(macho_file, self.target)) |index|
+            index
+        else
+            macho_file.getAtomIndexForSymbol(self.target),
+        else => macho_file.getAtomIndexForSymbol(self.target),
+    };
 }
 
 pub fn resolve(self: Relocation, macho_file: *MachO, atom_index: Atom.Index, code: []u8) void {
@@ -64,13 +68,22 @@ pub fn resolve(self: Relocation, macho_file: *MachO, atom_index: Atom.Index, cod
 
     const target_atom_index = self.getTargetAtomIndex(macho_file).?; // Oops, you didn't check if the relocation can be resolved with isResolvable().
     const target_atom = macho_file.getAtom(target_atom_index);
-    const target_addr = @intCast(i64, target_atom.getSymbol(macho_file).n_value) + self.addend;
+
+    const target_addr: i64 = switch (self.type) {
+        .tlv_initializer => blk: {
+            assert(self.addend == 0); // Addend here makes no sense.
+            const header = macho_file.sections.items(.header)[macho_file.thread_data_section_index.?];
+            const target_sym = target_atom.getSymbol(macho_file);
+            break :blk @intCast(i64, target_sym.n_value - header.addr);
+        },
+        else => @intCast(i64, target_atom.getSymbol(macho_file).n_value) + self.addend,
+    };
 
     log.debug("  ({x}: [() => 0x{x} ({s})) ({s})", .{
         source_addr,
         target_addr,
         macho_file.getSymbolName(self.target),
-        self.fmtType(macho_file.base.options.target),
+        @tagName(self.type),
     });
 
     switch (arch) {
@@ -81,18 +94,9 @@ pub fn resolve(self: Relocation, macho_file: *MachO, atom_index: Atom.Index, cod
 }
 
 fn resolveAarch64(self: Relocation, source_addr: u64, target_addr: i64, code: []u8) void {
-    const rel_type = @intToEnum(macho.reloc_type_arm64, self.type);
-    if (rel_type == .ARM64_RELOC_UNSIGNED) {
-        return switch (self.length) {
-            2 => mem.writeIntLittle(u32, code[self.offset..][0..4], @truncate(u32, @bitCast(u64, target_addr))),
-            3 => mem.writeIntLittle(u64, code[self.offset..][0..8], @bitCast(u64, target_addr)),
-            else => unreachable,
-        };
-    }
-
-    var buffer = code[self.offset..][0..4];
-    switch (rel_type) {
-        .ARM64_RELOC_BRANCH26 => {
+    var buffer = code[self.offset..];
+    switch (self.type) {
+        .branch => {
             const displacement = math.cast(
                 i28,
                 @intCast(i64, target_addr) - @intCast(i64, source_addr),
@@ -101,15 +105,12 @@ fn resolveAarch64(self: Relocation, source_addr: u64, target_addr: i64, code: []
                 .unconditional_branch_immediate = mem.bytesToValue(meta.TagPayload(
                     aarch64.Instruction,
                     aarch64.Instruction.unconditional_branch_immediate,
-                ), buffer),
+                ), buffer[0..4]),
             };
             inst.unconditional_branch_immediate.imm26 = @truncate(u26, @bitCast(u28, displacement >> 2));
-            mem.writeIntLittle(u32, buffer, inst.toU32());
+            mem.writeIntLittle(u32, buffer[0..4], inst.toU32());
         },
-        .ARM64_RELOC_PAGE21,
-        .ARM64_RELOC_GOT_LOAD_PAGE21,
-        .ARM64_RELOC_TLVP_LOAD_PAGE21,
-        => {
+        .page, .got_page => {
             const source_page = @intCast(i32, source_addr >> 12);
             const target_page = @intCast(i32, target_addr >> 12);
             const pages = @bitCast(u21, @intCast(i21, target_page - source_page));
@@ -117,31 +118,29 @@ fn resolveAarch64(self: Relocation, source_addr: u64, target_addr: i64, code: []
                 .pc_relative_address = mem.bytesToValue(meta.TagPayload(
                     aarch64.Instruction,
                     aarch64.Instruction.pc_relative_address,
-                ), buffer),
+                ), buffer[0..4]),
             };
             inst.pc_relative_address.immhi = @truncate(u19, pages >> 2);
             inst.pc_relative_address.immlo = @truncate(u2, pages);
-            mem.writeIntLittle(u32, buffer, inst.toU32());
+            mem.writeIntLittle(u32, buffer[0..4], inst.toU32());
         },
-        .ARM64_RELOC_PAGEOFF12,
-        .ARM64_RELOC_GOT_LOAD_PAGEOFF12,
-        => {
+        .pageoff, .got_pageoff => {
             const narrowed = @truncate(u12, @intCast(u64, target_addr));
-            if (isArithmeticOp(buffer)) {
+            if (isArithmeticOp(buffer[0..4])) {
                 var inst = aarch64.Instruction{
                     .add_subtract_immediate = mem.bytesToValue(meta.TagPayload(
                         aarch64.Instruction,
                         aarch64.Instruction.add_subtract_immediate,
-                    ), buffer),
+                    ), buffer[0..4]),
                 };
                 inst.add_subtract_immediate.imm12 = narrowed;
-                mem.writeIntLittle(u32, buffer, inst.toU32());
+                mem.writeIntLittle(u32, buffer[0..4], inst.toU32());
             } else {
                 var inst = aarch64.Instruction{
                     .load_store_register = mem.bytesToValue(meta.TagPayload(
                         aarch64.Instruction,
                         aarch64.Instruction.load_store_register,
-                    ), buffer),
+                    ), buffer[0..4]),
                 };
                 const offset: u12 = blk: {
                     if (inst.load_store_register.size == 0) {
@@ -157,89 +156,25 @@ fn resolveAarch64(self: Relocation, source_addr: u64, target_addr: i64, code: []
                     }
                 };
                 inst.load_store_register.offset = offset;
-                mem.writeIntLittle(u32, buffer, inst.toU32());
+                mem.writeIntLittle(u32, buffer[0..4], inst.toU32());
             }
         },
-        .ARM64_RELOC_TLVP_LOAD_PAGEOFF12 => {
-            const RegInfo = struct {
-                rd: u5,
-                rn: u5,
-                size: u2,
-            };
-            const reg_info: RegInfo = blk: {
-                if (isArithmeticOp(buffer)) {
-                    const inst = mem.bytesToValue(meta.TagPayload(
-                        aarch64.Instruction,
-                        aarch64.Instruction.add_subtract_immediate,
-                    ), buffer);
-                    break :blk .{
-                        .rd = inst.rd,
-                        .rn = inst.rn,
-                        .size = inst.sf,
-                    };
-                } else {
-                    const inst = mem.bytesToValue(meta.TagPayload(
-                        aarch64.Instruction,
-                        aarch64.Instruction.load_store_register,
-                    ), buffer);
-                    break :blk .{
-                        .rd = inst.rt,
-                        .rn = inst.rn,
-                        .size = inst.size,
-                    };
-                }
-            };
-            const narrowed = @truncate(u12, @intCast(u64, target_addr));
-            var inst = aarch64.Instruction{
-                .add_subtract_immediate = .{
-                    .rd = reg_info.rd,
-                    .rn = reg_info.rn,
-                    .imm12 = narrowed,
-                    .sh = 0,
-                    .s = 0,
-                    .op = 0,
-                    .sf = @truncate(u1, reg_info.size),
-                },
-            };
-            mem.writeIntLittle(u32, buffer, inst.toU32());
-        },
-        .ARM64_RELOC_POINTER_TO_GOT => {
-            const result = @intCast(i32, @intCast(i64, target_addr) - @intCast(i64, source_addr));
-            mem.writeIntLittle(i32, buffer, result);
+        .tlv_initializer, .unsigned => switch (self.length) {
+            2 => mem.writeIntLittle(u32, buffer[0..4], @truncate(u32, @bitCast(u64, target_addr))),
+            3 => mem.writeIntLittle(u64, buffer[0..8], @bitCast(u64, target_addr)),
+            else => unreachable,
         },
-        .ARM64_RELOC_SUBTRACTOR => unreachable,
-        .ARM64_RELOC_ADDEND => unreachable,
-        .ARM64_RELOC_UNSIGNED => unreachable,
+        .got, .signed, .tlv => unreachable, // Invalid target architecture.
     }
 }
 
 fn resolveX8664(self: Relocation, source_addr: u64, target_addr: i64, code: []u8) void {
-    const rel_type = @intToEnum(macho.reloc_type_x86_64, self.type);
-    switch (rel_type) {
-        .X86_64_RELOC_BRANCH,
-        .X86_64_RELOC_GOT,
-        .X86_64_RELOC_GOT_LOAD,
-        .X86_64_RELOC_TLV,
-        => {
+    switch (self.type) {
+        .branch, .got, .tlv, .signed => {
             const displacement = @intCast(i32, @intCast(i64, target_addr) - @intCast(i64, source_addr) - 4);
             mem.writeIntLittle(u32, code[self.offset..][0..4], @bitCast(u32, displacement));
         },
-        .X86_64_RELOC_SIGNED,
-        .X86_64_RELOC_SIGNED_1,
-        .X86_64_RELOC_SIGNED_2,
-        .X86_64_RELOC_SIGNED_4,
-        => {
-            const correction: u3 = switch (rel_type) {
-                .X86_64_RELOC_SIGNED => 0,
-                .X86_64_RELOC_SIGNED_1 => 1,
-                .X86_64_RELOC_SIGNED_2 => 2,
-                .X86_64_RELOC_SIGNED_4 => 4,
-                else => unreachable,
-            };
-            const displacement = @intCast(i32, target_addr - @intCast(i64, source_addr + correction + 4));
-            mem.writeIntLittle(u32, code[self.offset..][0..4], @bitCast(u32, displacement));
-        },
-        .X86_64_RELOC_UNSIGNED => {
+        .tlv_initializer, .unsigned => {
             switch (self.length) {
                 2 => {
                     mem.writeIntLittle(u32, code[self.offset..][0..4], @truncate(u32, @bitCast(u64, target_addr)));
@@ -250,7 +185,7 @@ fn resolveX8664(self: Relocation, source_addr: u64, target_addr: i64, code: []u8
                 else => unreachable,
             }
         },
-        .X86_64_RELOC_SUBTRACTOR => unreachable,
+        .got_page, .got_pageoff, .page, .pageoff => unreachable, // Invalid target architecture.
     }
 }
 
@@ -258,3 +193,18 @@ inline fn isArithmeticOp(inst: *const [4]u8) bool {
     const group_decode = @truncate(u5, inst[3]);
     return ((group_decode >> 2) == 4);
 }
+
+const Relocation = @This();
+
+const std = @import("std");
+const aarch64 = @import("../../arch/aarch64/bits.zig");
+const assert = std.debug.assert;
+const log = std.log.scoped(.link);
+const macho = std.macho;
+const math = std.math;
+const mem = std.mem;
+const meta = std.meta;
+
+const Atom = @import("Atom.zig");
+const MachO = @import("../MachO.zig");
+const SymbolWithLoc = MachO.SymbolWithLoc;