From 72dec90bfdb60a0ca2ac1b743db472d2e689414e Mon Sep 17 00:00:00 2001 From: Cherry Zhang Date: Sat, 24 Oct 2020 13:14:36 -0400 Subject: runtime: set up TLS without cgo on darwin/arm64 Currently, on darwin/arm64 we set up TLS using cgo. TLS is not set for pure Go programs. As we use libc for syscalls on darwin, we need to save the G register before the libc call. Otherwise it is not signal-safe, as a signal may land during the execution of a libc function, where the G register may be clobbered. This CL initializes TLS in Go, by calling the pthread functions directly without cgo. This makes it possible to save the G register to TLS in pure Go programs (done in a later CL). Inspired by Elias's CL 209197. Write the logic in Go instead of assembly. Updates #38485, #35853. Change-Id: I257ba2a411ad387b2f4d50d10129d37fec7a226e Reviewed-on: https://go-review.googlesource.com/c/go/+/265118 Trust: Cherry Zhang Trust: Elias Naur Run-TryBot: Cherry Zhang TryBot-Result: Go Bot Reviewed-by: Ian Lance Taylor --- src/runtime/sys_darwin_arm64.go | 62 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 62 insertions(+) create mode 100644 src/runtime/sys_darwin_arm64.go (limited to 'src/runtime/sys_darwin_arm64.go') diff --git a/src/runtime/sys_darwin_arm64.go b/src/runtime/sys_darwin_arm64.go new file mode 100644 index 0000000000..9c14f33a1c --- /dev/null +++ b/src/runtime/sys_darwin_arm64.go @@ -0,0 +1,62 @@ +// Copyright 2020 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package runtime + +import ( + "runtime/internal/sys" + "unsafe" +) + +// libc function wrappers. Must run on system stack. + +//go:nosplit +//go:cgo_unsafe_args +func g0_pthread_key_create(k *pthreadkey, destructor uintptr) int32 { + return asmcgocall(unsafe.Pointer(funcPC(pthread_key_create_trampoline)), unsafe.Pointer(&k)) +} +func pthread_key_create_trampoline() + +//go:nosplit +//go:cgo_unsafe_args +func g0_pthread_setspecific(k pthreadkey, value uintptr) int32 { + return asmcgocall(unsafe.Pointer(funcPC(pthread_setspecific_trampoline)), unsafe.Pointer(&k)) +} +func pthread_setspecific_trampoline() + +//go:cgo_import_dynamic libc_pthread_key_create pthread_key_create "/usr/lib/libSystem.B.dylib" +//go:cgo_import_dynamic libc_pthread_setspecific pthread_setspecific "/usr/lib/libSystem.B.dylib" + +// tlsinit allocates a thread-local storage slot for g. +// +// It finds the first available slot using pthread_key_create and uses +// it as the offset value for runtime.tlsg. +// +// This runs at startup on g0 stack, but before g is set, so it must +// not split stack (transitively). g is expected to be nil, so things +// (e.g. asmcgocall) will skip saving or reading g. +// +//go:nosplit +func tlsinit(tlsg *uintptr, tlsbase *[_PTHREAD_KEYS_MAX]uintptr) { + var k pthreadkey + err := g0_pthread_key_create(&k, 0) + if err != 0 { + abort() + } + + const magic = 0xc476c475c47957 + err = g0_pthread_setspecific(k, magic) + if err != 0 { + abort() + } + + for i, x := range tlsbase { + if x == magic { + *tlsg = uintptr(i * sys.PtrSize) + g0_pthread_setspecific(k, 0) + return + } + } + abort() +} -- cgit v1.3