1// Copyright 2020 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package runtime
6
7import (
8	"internal/abi"
9	"internal/goarch"
10	"unsafe"
11)
12
13// libc function wrappers. Must run on system stack.
14
15//go:nosplit
16//go:cgo_unsafe_args
17func g0_pthread_key_create(k *pthreadkey, destructor uintptr) int32 {
18	ret := asmcgocall(unsafe.Pointer(abi.FuncPCABI0(pthread_key_create_trampoline)), unsafe.Pointer(&k))
19	KeepAlive(k)
20	return ret
21}
22func pthread_key_create_trampoline()
23
24//go:nosplit
25//go:cgo_unsafe_args
26func g0_pthread_setspecific(k pthreadkey, value uintptr) int32 {
27	return asmcgocall(unsafe.Pointer(abi.FuncPCABI0(pthread_setspecific_trampoline)), unsafe.Pointer(&k))
28}
29func pthread_setspecific_trampoline()
30
31//go:cgo_import_dynamic libc_pthread_key_create pthread_key_create "/usr/lib/libSystem.B.dylib"
32//go:cgo_import_dynamic libc_pthread_setspecific pthread_setspecific "/usr/lib/libSystem.B.dylib"
33
34// tlsinit allocates a thread-local storage slot for g.
35//
36// It finds the first available slot using pthread_key_create and uses
37// it as the offset value for runtime.tlsg.
38//
39// This runs at startup on g0 stack, but before g is set, so it must
40// not split stack (transitively). g is expected to be nil, so things
41// (e.g. asmcgocall) will skip saving or reading g.
42//
43//go:nosplit
44func tlsinit(tlsg *uintptr, tlsbase *[_PTHREAD_KEYS_MAX]uintptr) {
45	var k pthreadkey
46	err := g0_pthread_key_create(&k, 0)
47	if err != 0 {
48		abort()
49	}
50
51	const magic = 0xc476c475c47957
52	err = g0_pthread_setspecific(k, magic)
53	if err != 0 {
54		abort()
55	}
56
57	for i, x := range tlsbase {
58		if x == magic {
59			*tlsg = uintptr(i * goarch.PtrSize)
60			g0_pthread_setspecific(k, 0)
61			return
62		}
63	}
64	abort()
65}
66