// Copyright 2016 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Support for memory sanitizer. See runtime/cgo/sigaction.go.
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// +build linux,amd64 freebsd,amd64 linux,arm64
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package runtime
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import "unsafe"
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// _cgo_sigaction is filled in by runtime/cgo when it is linked into the
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// program, so it is only non-nil when using cgo.
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//go:linkname _cgo_sigaction _cgo_sigaction
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var _cgo_sigaction unsafe.Pointer
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//go:nosplit
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//go:nowritebarrierrec
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func sigaction(sig uint32, new, old *sigactiont) {
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// The runtime package is explicitly blacklisted from sanitizer
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// instrumentation in racewalk.go, but we might be calling into instrumented C
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// functions here — so we need the pointer parameters to be properly marked.
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//
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// Mark the input as having been written before the call and the output as
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// read after.
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if msanenabled && new != nil {
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msanwrite(unsafe.Pointer(new), unsafe.Sizeof(*new))
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}
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if _cgo_sigaction == nil || inForkedChild {
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sysSigaction(sig, new, old)
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} else {
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// We need to call _cgo_sigaction, which means we need a big enough stack
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// for C. To complicate matters, we may be in libpreinit (before the
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// runtime has been initialized) or in an asynchronous signal handler (with
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// the current thread in transition between goroutines, or with the g0
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// system stack already in use).
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var ret int32
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g := getg()
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sp := uintptr(unsafe.Pointer(&sig))
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switch {
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case g == nil:
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// No g: we're on a C stack or a signal stack.
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ret = callCgoSigaction(uintptr(sig), new, old)
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case sp < g.stack.lo || sp >= g.stack.hi:
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// We're no longer on g's stack, so we must be handling a signal. It's
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// possible that we interrupted the thread during a transition between g
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// and g0, so we should stay on the current stack to avoid corrupting g0.
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ret = callCgoSigaction(uintptr(sig), new, old)
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default:
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// We're running on g's stack, so either we're not in a signal handler or
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// the signal handler has set the correct g. If we're on gsignal or g0,
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// systemstack will make the call directly; otherwise, it will switch to
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// g0 to ensure we have enough room to call a libc function.
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//
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// The function literal that we pass to systemstack is not nosplit, but
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// that's ok: we'll be running on a fresh, clean system stack so the stack
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// check will always succeed anyway.
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systemstack(func() {
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ret = callCgoSigaction(uintptr(sig), new, old)
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})
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}
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const EINVAL = 22
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if ret == EINVAL {
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// libc reserves certain signals — normally 32-33 — for pthreads, and
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// returns EINVAL for sigaction calls on those signals. If we get EINVAL,
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// fall back to making the syscall directly.
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sysSigaction(sig, new, old)
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}
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}
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if msanenabled && old != nil {
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msanread(unsafe.Pointer(old), unsafe.Sizeof(*old))
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}
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}
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// callCgoSigaction calls the sigaction function in the runtime/cgo package
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// using the GCC calling convention. It is implemented in assembly.
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//go:noescape
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func callCgoSigaction(sig uintptr, new, old *sigactiont) int32
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