Black Lives Matter. Support the Equal Justice Initiative.

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 sanitizers. See runtime/cgo/sigaction.go.
     6  
     7  //go:build (linux && amd64) || (freebsd && amd64) || (linux && arm64) || (linux && ppc64le)
     8  // +build linux,amd64 freebsd,amd64 linux,arm64 linux,ppc64le
     9  
    10  package runtime
    11  
    12  import "unsafe"
    13  
    14  // _cgo_sigaction is filled in by runtime/cgo when it is linked into the
    15  // program, so it is only non-nil when using cgo.
    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  
    32  	if _cgo_sigaction == nil || inForkedChild {
    33  		sysSigaction(sig, new, old)
    34  	} else {
    35  		// We need to call _cgo_sigaction, which means we need a big enough stack
    36  		// for C.  To complicate matters, we may be in libpreinit (before the
    37  		// runtime has been initialized) or in an asynchronous signal handler (with
    38  		// the current thread in transition between goroutines, or with the g0
    39  		// system stack already in use).
    40  
    41  		var ret int32
    42  
    43  		var g *g
    44  		if mainStarted {
    45  			g = getg()
    46  		}
    47  		sp := uintptr(unsafe.Pointer(&sig))
    48  		switch {
    49  		case g == nil:
    50  			// No g: we're on a C stack or a signal stack.
    51  			ret = callCgoSigaction(uintptr(sig), new, old)
    52  		case sp < g.stack.lo || sp >= g.stack.hi:
    53  			// We're no longer on g's stack, so we must be handling a signal.  It's
    54  			// possible that we interrupted the thread during a transition between g
    55  			// and g0, so we should stay on the current stack to avoid corrupting g0.
    56  			ret = callCgoSigaction(uintptr(sig), new, old)
    57  		default:
    58  			// We're running on g's stack, so either we're not in a signal handler or
    59  			// the signal handler has set the correct g.  If we're on gsignal or g0,
    60  			// systemstack will make the call directly; otherwise, it will switch to
    61  			// g0 to ensure we have enough room to call a libc function.
    62  			//
    63  			// The function literal that we pass to systemstack is not nosplit, but
    64  			// that's ok: we'll be running on a fresh, clean system stack so the stack
    65  			// check will always succeed anyway.
    66  			systemstack(func() {
    67  				ret = callCgoSigaction(uintptr(sig), new, old)
    68  			})
    69  		}
    70  
    71  		const EINVAL = 22
    72  		if ret == EINVAL {
    73  			// libc reserves certain signals — normally 32-33 — for pthreads, and
    74  			// returns EINVAL for sigaction calls on those signals.  If we get EINVAL,
    75  			// fall back to making the syscall directly.
    76  			sysSigaction(sig, new, old)
    77  		}
    78  	}
    79  
    80  	if msanenabled && old != nil {
    81  		msanread(unsafe.Pointer(old), unsafe.Sizeof(*old))
    82  	}
    83  }
    84  
    85  // callCgoSigaction calls the sigaction function in the runtime/cgo package
    86  // using the GCC calling convention. It is implemented in assembly.
    87  //go:noescape
    88  func callCgoSigaction(sig uintptr, new, old *sigactiont) int32
    89  

View as plain text