Source file src/runtime/cgo_sigaction.go

Documentation: runtime

     1  // Copyright 2016 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  
     5  // Support for memory sanitizer. See runtime/cgo/sigaction.go.
     6  
     7  // +build linux,amd64 freebsd,amd64 linux,arm64
     8  
     9  package runtime
    10  
    11  import "unsafe"
    12  
    13  // _cgo_sigaction is filled in by runtime/cgo when it is linked into the
    14  // program, so it is only non-nil when using cgo.
    15  //go:linkname _cgo_sigaction _cgo_sigaction
    16  var _cgo_sigaction unsafe.Pointer
    17  
    18  //go:nosplit
    19  //go:nowritebarrierrec
    20  func sigaction(sig uint32, new, old *sigactiont) {
    21  	// The runtime package is explicitly blacklisted from sanitizer
    22  	// instrumentation in racewalk.go, but we might be calling into instrumented C
    23  	// functions here — so we need the pointer parameters to be properly marked.
    24  	//
    25  	// Mark the input as having been written before the call and the output as
    26  	// read after.
    27  	if msanenabled && new != nil {
    28  		msanwrite(unsafe.Pointer(new), unsafe.Sizeof(*new))
    29  	}
    30  
    31  	if _cgo_sigaction == nil || inForkedChild {
    32  		sysSigaction(sig, new, old)
    33  	} else {
    34  		// We need to call _cgo_sigaction, which means we need a big enough stack
    35  		// for C.  To complicate matters, we may be in libpreinit (before the
    36  		// runtime has been initialized) or in an asynchronous signal handler (with
    37  		// the current thread in transition between goroutines, or with the g0
    38  		// system stack already in use).
    39  
    40  		var ret int32
    41  
    42  		var g *g
    43  		if mainStarted {
    44  			g = getg()
    45  		}
    46  		sp := uintptr(unsafe.Pointer(&sig))
    47  		switch {
    48  		case g == nil:
    49  			// No g: we're on a C stack or a signal stack.
    50  			ret = callCgoSigaction(uintptr(sig), new, old)
    51  		case sp < g.stack.lo || sp >= g.stack.hi:
    52  			// We're no longer on g's stack, so we must be handling a signal.  It's
    53  			// possible that we interrupted the thread during a transition between g
    54  			// and g0, so we should stay on the current stack to avoid corrupting g0.
    55  			ret = callCgoSigaction(uintptr(sig), new, old)
    56  		default:
    57  			// We're running on g's stack, so either we're not in a signal handler or
    58  			// the signal handler has set the correct g.  If we're on gsignal or g0,
    59  			// systemstack will make the call directly; otherwise, it will switch to
    60  			// g0 to ensure we have enough room to call a libc function.
    61  			//
    62  			// The function literal that we pass to systemstack is not nosplit, but
    63  			// that's ok: we'll be running on a fresh, clean system stack so the stack
    64  			// check will always succeed anyway.
    65  			systemstack(func() {
    66  				ret = callCgoSigaction(uintptr(sig), new, old)
    67  			})
    68  		}
    69  
    70  		const EINVAL = 22
    71  		if ret == EINVAL {
    72  			// libc reserves certain signals — normally 32-33 — for pthreads, and
    73  			// returns EINVAL for sigaction calls on those signals.  If we get EINVAL,
    74  			// fall back to making the syscall directly.
    75  			sysSigaction(sig, new, old)
    76  		}
    77  	}
    78  
    79  	if msanenabled && old != nil {
    80  		msanread(unsafe.Pointer(old), unsafe.Sizeof(*old))
    81  	}
    82  }
    83  
    84  // callCgoSigaction calls the sigaction function in the runtime/cgo package
    85  // using the GCC calling convention. It is implemented in assembly.
    86  //go:noescape
    87  func callCgoSigaction(sig uintptr, new, old *sigactiont) int32
    88  

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