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  //
    16  //go:linkname _cgo_sigaction _cgo_sigaction
    17  var _cgo_sigaction unsafe.Pointer
    18  
    19  //go:nosplit
    20  //go:nowritebarrierrec
    21  func sigaction(sig uint32, new, old *sigactiont) {
    22  	// racewalk.go avoids adding sanitizing instrumentation to package runtime,
    23  	// but we might be calling into instrumented C functions here,
    24  	// so we need the pointer parameters to be properly marked.
    25  	//
    26  	// Mark the input as having been written before the call
    27  	// and the output as read after.
    28  	if msanenabled && new != nil {
    29  		msanwrite(unsafe.Pointer(new), unsafe.Sizeof(*new))
    30  	}
    31  	if asanenabled && new != nil {
    32  		asanwrite(unsafe.Pointer(new), unsafe.Sizeof(*new))
    33  	}
    34  	if _cgo_sigaction == nil || inForkedChild {
    35  		sysSigaction(sig, new, old)
    36  	} else {
    37  		// We need to call _cgo_sigaction, which means we need a big enough stack
    38  		// for C.  To complicate matters, we may be in libpreinit (before the
    39  		// runtime has been initialized) or in an asynchronous signal handler (with
    40  		// the current thread in transition between goroutines, or with the g0
    41  		// system stack already in use).
    42  
    43  		var ret int32
    44  
    45  		var g *g
    46  		if mainStarted {
    47  			g = getg()
    48  		}
    49  		sp := uintptr(unsafe.Pointer(&sig))
    50  		switch {
    51  		case g == nil:
    52  			// No g: we're on a C stack or a signal stack.
    53  			ret = callCgoSigaction(uintptr(sig), new, old)
    54  		case sp < g.stack.lo || sp >= g.stack.hi:
    55  			// We're no longer on g's stack, so we must be handling a signal.  It's
    56  			// possible that we interrupted the thread during a transition between g
    57  			// and g0, so we should stay on the current stack to avoid corrupting g0.
    58  			ret = callCgoSigaction(uintptr(sig), new, old)
    59  		default:
    60  			// We're running on g's stack, so either we're not in a signal handler or
    61  			// the signal handler has set the correct g.  If we're on gsignal or g0,
    62  			// systemstack will make the call directly; otherwise, it will switch to
    63  			// g0 to ensure we have enough room to call a libc function.
    64  			//
    65  			// The function literal that we pass to systemstack is not nosplit, but
    66  			// that's ok: we'll be running on a fresh, clean system stack so the stack
    67  			// check will always succeed anyway.
    68  			systemstack(func() {
    69  				ret = callCgoSigaction(uintptr(sig), new, old)
    70  			})
    71  		}
    72  
    73  		const EINVAL = 22
    74  		if ret == EINVAL {
    75  			// libc reserves certain signals — normally 32-33 — for pthreads, and
    76  			// returns EINVAL for sigaction calls on those signals.  If we get EINVAL,
    77  			// fall back to making the syscall directly.
    78  			sysSigaction(sig, new, old)
    79  		}
    80  	}
    81  
    82  	if msanenabled && old != nil {
    83  		msanread(unsafe.Pointer(old), unsafe.Sizeof(*old))
    84  	}
    85  	if asanenabled && old != nil {
    86  		asanread(unsafe.Pointer(old), unsafe.Sizeof(*old))
    87  	}
    88  }
    89  
    90  // callCgoSigaction calls the sigaction function in the runtime/cgo package
    91  // using the GCC calling convention. It is implemented in assembly.
    92  //
    93  //go:noescape
    94  func callCgoSigaction(sig uintptr, new, old *sigactiont) int32
    95
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