/
start.zig
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/
start.zig
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// This file is included in the compilation unit when exporting an executable.
const root = @import("root");
const std = @import("std.zig");
const builtin = std.builtin;
const assert = std.debug.assert;
const uefi = std.os.uefi;
var starting_stack_ptr: [*]usize = undefined;
const is_wasm = switch (builtin.arch) {
.wasm32, .wasm64 => true,
else => false,
};
const is_mips = switch (builtin.arch) {
.mips, .mipsel, .mips64, .mips64el => true,
else => false,
};
const start_sym_name = if (is_mips) "__start" else "_start";
comptime {
if (builtin.output_mode == .Lib and builtin.link_mode == .Dynamic) {
if (builtin.os == .windows and !@hasDecl(root, "_DllMainCRTStartup")) {
@export("_DllMainCRTStartup", _DllMainCRTStartup, .Strong);
}
} else if (builtin.output_mode == .Exe or @hasDecl(root, "main")) {
if (builtin.link_libc and @hasDecl(root, "main")) {
if (@typeInfo(@TypeOf(root.main)).Fn.calling_convention != .C) {
@export("main", main, .Weak);
}
} else if (builtin.os == .windows) {
if (!@hasDecl(root, "WinMain") and !@hasDecl(root, "WinMainCRTStartup")) {
@export("WinMainCRTStartup", WinMainCRTStartup, .Strong);
}
} else if (builtin.os == .uefi) {
if (!@hasDecl(root, "EfiMain")) @export("EfiMain", EfiMain, .Strong);
} else if (is_wasm and builtin.os == .freestanding) {
if (!@hasDecl(root, start_sym_name)) @export(start_sym_name, wasm_freestanding_start, .Strong);
} else if (builtin.os != .other and builtin.os != .freestanding) {
if (!@hasDecl(root, start_sym_name)) @export(start_sym_name, _start, .Strong);
}
}
}
stdcallcc fn _DllMainCRTStartup(
hinstDLL: std.os.windows.HINSTANCE,
fdwReason: std.os.windows.DWORD,
lpReserved: std.os.windows.LPVOID,
) std.os.windows.BOOL {
if (@hasDecl(root, "DllMain")) {
return root.DllMain(hinstDLL, fdwReason, lpReserved);
}
return std.os.windows.TRUE;
}
extern fn wasm_freestanding_start() void {
// This is marked inline because for some reason LLVM in release mode fails to inline it,
// and we want fewer call frames in stack traces.
_ = @call(.{ .modifier = .always_inline }, callMain, .{});
}
extern fn EfiMain(handle: uefi.Handle, system_table: *uefi.tables.SystemTable) usize {
const bad_efi_main_ret = "expected return type of main to be 'void', 'noreturn', or 'usize'";
uefi.handle = handle;
uefi.system_table = system_table;
switch (@typeInfo(@TypeOf(root.main).ReturnType)) {
.NoReturn => {
root.main();
},
.Void => {
root.main();
return 0;
},
.Int => |info| {
if (info.bits != @typeInfo(usize).Int.bits) {
@compileError(bad_efi_main_ret);
}
return root.main();
},
else => @compileError(bad_efi_main_ret),
}
}
nakedcc fn _start() noreturn {
if (builtin.os == builtin.Os.wasi) {
// This is marked inline because for some reason LLVM in release mode fails to inline it,
// and we want fewer call frames in stack traces.
std.os.wasi.proc_exit(@call(.{ .modifier = .always_inline }, callMain, .{}));
}
switch (builtin.arch) {
.x86_64 => {
starting_stack_ptr = asm (""
: [argc] "={rsp}" (-> [*]usize)
);
},
.i386 => {
starting_stack_ptr = asm (""
: [argc] "={esp}" (-> [*]usize)
);
},
.aarch64, .aarch64_be, .arm => {
starting_stack_ptr = asm ("mov %[argc], sp"
: [argc] "=r" (-> [*]usize)
);
},
.riscv64 => {
starting_stack_ptr = asm ("mv %[argc], sp"
: [argc] "=r" (-> [*]usize)
);
},
.mipsel => {
// Need noat here because LLVM is free to pick any register
starting_stack_ptr = asm (
\\ .set noat
\\ move %[argc], $sp
: [argc] "=r" (-> [*]usize)
);
},
else => @compileError("unsupported arch"),
}
// If LLVM inlines stack variables into _start, they will overwrite
// the command line argument data.
@call(.{ .modifier = .never_inline }, posixCallMainAndExit, .{});
}
stdcallcc fn WinMainCRTStartup() noreturn {
@setAlignStack(16);
if (!builtin.single_threaded) {
_ = @import("start_windows_tls.zig");
}
std.debug.maybeEnableSegfaultHandler();
std.os.windows.kernel32.ExitProcess(initEventLoopAndCallMain());
}
// TODO https://github.com/ziglang/zig/issues/265
fn posixCallMainAndExit() noreturn {
if (builtin.os == builtin.Os.freebsd) {
@setAlignStack(16);
}
const argc = starting_stack_ptr[0];
const argv = @ptrCast([*][*:0]u8, starting_stack_ptr + 1);
const envp_optional = @ptrCast([*:null]?[*:0]u8, argv + argc + 1);
var envp_count: usize = 0;
while (envp_optional[envp_count]) |_| : (envp_count += 1) {}
const envp = @ptrCast([*][*:0]u8, envp_optional)[0..envp_count];
if (builtin.os == .linux) {
// Find the beginning of the auxiliary vector
const auxv = @ptrCast([*]std.elf.Auxv, envp.ptr + envp_count + 1);
std.os.linux.elf_aux_maybe = auxv;
// Initialize the TLS area
const gnu_stack_phdr = std.os.linux.tls.initTLS() orelse @panic("ELF missing stack size");
if (std.os.linux.tls.tls_image) |tls_img| {
const tls_addr = std.os.linux.tls.allocateTLS(tls_img.alloc_size);
const tp = std.os.linux.tls.copyTLS(tls_addr);
std.os.linux.tls.setThreadPointer(tp);
}
// TODO This is disabled because what should we do when linking libc and this code
// does not execute? And also it's causing a test failure in stack traces in release modes.
//// Linux ignores the stack size from the ELF file, and instead always does 8 MiB. A further
//// problem is that it uses PROT_GROWSDOWN which prevents stores to addresses too far down
//// the stack and requires "probing". So here we allocate our own stack.
//const wanted_stack_size = gnu_stack_phdr.p_memsz;
//assert(wanted_stack_size % std.mem.page_size == 0);
//// Allocate an extra page as the guard page.
//const total_size = wanted_stack_size + std.mem.page_size;
//const new_stack = std.os.mmap(
// null,
// total_size,
// std.os.PROT_READ | std.os.PROT_WRITE,
// std.os.MAP_PRIVATE | std.os.MAP_ANONYMOUS,
// -1,
// 0,
//) catch @panic("out of memory");
//std.os.mprotect(new_stack[0..std.mem.page_size], std.os.PROT_NONE) catch {};
//std.os.exit(@call(.{.stack = new_stack}, callMainWithArgs, .{argc, argv, envp}));
}
std.os.exit(@call(.{ .modifier = .always_inline }, callMainWithArgs, .{ argc, argv, envp }));
}
fn callMainWithArgs(argc: usize, argv: [*][*:0]u8, envp: [][*:0]u8) u8 {
std.os.argv = argv[0..argc];
std.os.environ = envp;
std.debug.maybeEnableSegfaultHandler();
return initEventLoopAndCallMain();
}
extern fn main(c_argc: i32, c_argv: [*][*:0]u8, c_envp: [*:null]?[*:0]u8) i32 {
var env_count: usize = 0;
while (c_envp[env_count] != null) : (env_count += 1) {}
const envp = @ptrCast([*][*:0]u8, c_envp)[0..env_count];
return @call(.{ .modifier = .always_inline }, callMainWithArgs, .{ @intCast(usize, c_argc), c_argv, envp });
}
// General error message for a malformed return type
const bad_main_ret = "expected return type of main to be 'void', '!void', 'noreturn', 'u8', or '!u8'";
// This is marked inline because for some reason LLVM in release mode fails to inline it,
// and we want fewer call frames in stack traces.
inline fn initEventLoopAndCallMain() u8 {
if (std.event.Loop.instance) |loop| {
if (!@hasDecl(root, "event_loop")) {
loop.init() catch |err| {
std.debug.warn("error: {}\n", .{@errorName(err)});
if (@errorReturnTrace()) |trace| {
std.debug.dumpStackTrace(trace.*);
}
return 1;
};
defer loop.deinit();
var result: u8 = undefined;
var frame: @Frame(callMainAsync) = undefined;
_ = @asyncCall(&frame, &result, callMainAsync, loop);
loop.run();
return result;
}
}
// This is marked inline because for some reason LLVM in release mode fails to inline it,
// and we want fewer call frames in stack traces.
return @call(.{ .modifier = .always_inline }, callMain, .{});
}
async fn callMainAsync(loop: *std.event.Loop) u8 {
// This prevents the event loop from terminating at least until main() has returned.
loop.beginOneEvent();
defer loop.finishOneEvent();
return callMain();
}
// This is not marked inline because it is called with @asyncCall when
// there is an event loop.
pub fn callMain() u8 {
switch (@typeInfo(@TypeOf(root.main).ReturnType)) {
.NoReturn => {
root.main();
},
.Void => {
root.main();
return 0;
},
.Int => |info| {
if (info.bits != 8) {
@compileError(bad_main_ret);
}
return root.main();
},
.ErrorUnion => {
const result = root.main() catch |err| {
std.debug.warn("error: {}\n", .{@errorName(err)});
if (@errorReturnTrace()) |trace| {
std.debug.dumpStackTrace(trace.*);
}
return 1;
};
switch (@typeInfo(@TypeOf(result))) {
.Void => return 0,
.Int => |info| {
if (info.bits != 8) {
@compileError(bad_main_ret);
}
return result;
},
else => @compileError(bad_main_ret),
}
},
else => @compileError(bad_main_ret),
}
}