cgo_sigaction.go

     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 sanitizers. See runtime/cgo/sigaction.go.
     6  
     7  //go:build (linux && amd64) || (freebsd && amd64) || (linux && arm64) || (linux && ppc64le)
     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  	// racewalk.go avoids adding sanitizing instrumentation to package runtime,
    22  	// but we might be calling into instrumented C functions here,
    23  	// so we need the pointer parameters to be properly marked.
    24  	//
    25  	// Mark the input as having been written before the call
    26  	// and the output as read after.
    27  	if msanenabled && new != nil {
    28  		msanwrite(unsafe.Pointer(new), unsafe.Sizeof(*new))
    29  	}
    30  	if asanenabled && new != nil {
    31  		asanwrite(unsafe.Pointer(new), unsafe.Sizeof(*new))
    32  	}
    33  	if _cgo_sigaction == nil || inForkedChild {
    34  		sysSigaction(sig, new, old)
    35  	} else {
    36  		// We need to call _cgo_sigaction, which means we need a big enough stack
    37  		// for C.  To complicate matters, we may be in libpreinit (before the
    38  		// runtime has been initialized) or in an asynchronous signal handler (with
    39  		// the current thread in transition between goroutines, or with the g0
    40  		// system stack already in use).
    41  
    42  		var ret int32
    43  
    44  		var g *g
    45  		if mainStarted {
    46  			g = getg()
    47  		}
    48  		sp := uintptr(unsafe.Pointer(&sig))
    49  		switch {
    50  		case g == nil:
    51  			// No g: we're on a C stack or a signal stack.
    52  			ret = callCgoSigaction(uintptr(sig), new, old)
    53  		case sp < g.stack.lo || sp >= g.stack.hi:
    54  			// We're no longer on g's stack, so we must be handling a signal.  It's
    55  			// possible that we interrupted the thread during a transition between g
    56  			// and g0, so we should stay on the current stack to avoid corrupting g0.
    57  			ret = callCgoSigaction(uintptr(sig), new, old)
    58  		default:
    59  			// We're running on g's stack, so either we're not in a signal handler or
    60  			// the signal handler has set the correct g.  If we're on gsignal or g0,
    61  			// systemstack will make the call directly; otherwise, it will switch to
    62  			// g0 to ensure we have enough room to call a libc function.
    63  			//
    64  			// The function literal that we pass to systemstack is not nosplit, but
    65  			// that's ok: we'll be running on a fresh, clean system stack so the stack
    66  			// check will always succeed anyway.
    67  			systemstack(func() {
    68  				ret = callCgoSigaction(uintptr(sig), new, old)
    69  			})
    70  		}
    71  
    72  		const EINVAL = 22
    73  		if ret == EINVAL {
    74  			// libc reserves certain signals — normally 32-33 — for pthreads, and
    75  			// returns EINVAL for sigaction calls on those signals.  If we get EINVAL,
    76  			// fall back to making the syscall directly.
    77  			sysSigaction(sig, new, old)
    78  		}
    79  	}
    80  
    81  	if msanenabled && old != nil {
    82  		msanread(unsafe.Pointer(old), unsafe.Sizeof(*old))
    83  	}
    84  	if asanenabled && old != nil {
    85  		asanread(unsafe.Pointer(old), unsafe.Sizeof(*old))
    86  	}
    87  }
    88  
    89  // callCgoSigaction calls the sigaction function in the runtime/cgo package
    90  // using the GCC calling convention. It is implemented in assembly.
    91  //go:noescape
    92  func callCgoSigaction(sig uintptr, new, old *sigactiont) int32
    93
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