1const std = @import("std");
 2const builtin = @import("builtin");
 3const windows = std.os.windows;
 4
 5export var _tls_index: u32 = std.os.windows.TLS_OUT_OF_INDEXES;
 6export var _tls_start: ?*anyopaque linksection(".tls") = null;
 7export var _tls_end: ?*anyopaque linksection(".tls$ZZZ") = null;
 8export var __xl_a: windows.PIMAGE_TLS_CALLBACK linksection(".CRT$XLA") = null;
 9export var __xl_z: windows.PIMAGE_TLS_CALLBACK linksection(".CRT$XLZ") = null;
10
11comptime {
12    if (builtin.cpu.arch == .x86 and !builtin.abi.isGnu() and builtin.zig_backend != .stage2_c) {
13        // The __tls_array is the offset of the ThreadLocalStoragePointer field
14        // in the TEB block whose base address held in the %fs segment.
15        asm (
16            \\ .global __tls_array
17            \\ __tls_array = 0x2C
18        );
19    }
20}
21
22// TODO this is how I would like it to be expressed
23//export const _tls_used linksection(".rdata$T") = std.os.windows.IMAGE_TLS_DIRECTORY {
24//    .StartAddressOfRawData = @intFromPtr(&_tls_start),
25//    .EndAddressOfRawData = @intFromPtr(&_tls_end),
26//    .AddressOfIndex = @intFromPtr(&_tls_index),
27//    .AddressOfCallBacks = @intFromPtr(__xl_a),
28//    .SizeOfZeroFill = 0,
29//    .Characteristics = 0,
30//};
31// This is the workaround because we can't do @intFromPtr at comptime like that.
32pub const IMAGE_TLS_DIRECTORY = extern struct {
33    StartAddressOfRawData: *?*anyopaque,
34    EndAddressOfRawData: *?*anyopaque,
35    AddressOfIndex: *u32,
36    AddressOfCallBacks: [*:null]windows.PIMAGE_TLS_CALLBACK,
37    SizeOfZeroFill: u32,
38    Characteristics: u32,
39};
40export const _tls_used linksection(".rdata$T") = IMAGE_TLS_DIRECTORY{
41    .StartAddressOfRawData = &_tls_start,
42    .EndAddressOfRawData = &_tls_end,
43    .AddressOfIndex = &_tls_index,
44    // __xl_a is just a global variable containing a null pointer; the actual callbacks sit in
45    // between __xl_a and __xl_z. So we need to skip over __xl_a here. If there are no callbacks,
46    // this just means we point to __xl_z (the null terminator).
47    .AddressOfCallBacks = @as([*:null]windows.PIMAGE_TLS_CALLBACK, @ptrCast(&__xl_a)) + 1,
48    .SizeOfZeroFill = 0,
49    .Characteristics = 0,
50};