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