runtime: wrap darwin libc calls to keep profiler happy

The profiler reports "ExternalCode" when a profiler interrupt happens
while in libc code. Instead, keep track of the most recent Go frame
for the profiler to use.

There is a test for this using time.Now (runtime.TestTimePprof),
which will work once time.Now is moved to using libc (my next CL).

Change-Id: I940ea83edada482a482e2ab103d3a65589979464
Reviewed-on: https://go-review.googlesource.com/114798
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/sys_darwin.go

@@ -6,48 +6,74 @@ package runtime
 
 import "unsafe"
 
+// Call fn with arg as its argument. Return what fn returns.
+// fn is the raw pc value of the entry point of the desired function.
+// Switches to the system stack, if not already there.
+// Preserves the calling point as the location where a profiler traceback will begin.
+//go:nosplit
+func libcCall(fn, arg unsafe.Pointer) int32 {
+	// Leave caller's PC/SP/G around for traceback.
+	gp := getg()
+	var mp *m
+	if gp != nil {
+		mp = gp.m
+	}
+	if mp != nil {
+		mp.libcallg.set(gp)
+		mp.libcallpc = getcallerpc()
+		// sp must be the last, because once async cpu profiler finds
+		// all three values to be non-zero, it will use them
+		mp.libcallsp = getcallersp()
+	}
+	res := asmcgocall(fn, arg)
+	if mp != nil {
+		mp.libcallsp = 0
+	}
+	return res
+}
+
 // The *_trampoline functions convert from the Go calling convention to the C calling convention
 // and then call the underlying libc function.  They are defined in sys_darwin_$ARCH.s.
 
 //go:nosplit
 //go:cgo_unsafe_args
 func pthread_attr_init(attr *pthreadattr) int32 {
-	return asmcgocall(unsafe.Pointer(funcPC(pthread_attr_init_trampoline)), unsafe.Pointer(&attr))
+	return libcCall(unsafe.Pointer(funcPC(pthread_attr_init_trampoline)), unsafe.Pointer(&attr))
 }
 func pthread_attr_init_trampoline()
 
 //go:nosplit
 //go:cgo_unsafe_args
 func pthread_attr_setstacksize(attr *pthreadattr, size uintptr) int32 {
-	return asmcgocall(unsafe.Pointer(funcPC(pthread_attr_setstacksize_trampoline)), unsafe.Pointer(&attr))
+	return libcCall(unsafe.Pointer(funcPC(pthread_attr_setstacksize_trampoline)), unsafe.Pointer(&attr))
 }
 func pthread_attr_setstacksize_trampoline()
 
 //go:nosplit
 //go:cgo_unsafe_args
 func pthread_attr_setdetachstate(attr *pthreadattr, state int) int32 {
-	return asmcgocall(unsafe.Pointer(funcPC(pthread_attr_setdetachstate_trampoline)), unsafe.Pointer(&attr))
+	return libcCall(unsafe.Pointer(funcPC(pthread_attr_setdetachstate_trampoline)), unsafe.Pointer(&attr))
 }
 func pthread_attr_setdetachstate_trampoline()
 
 //go:nosplit
 //go:cgo_unsafe_args
 func pthread_create(attr *pthreadattr, start uintptr, arg unsafe.Pointer) int32 {
-	return asmcgocall(unsafe.Pointer(funcPC(pthread_create_trampoline)), unsafe.Pointer(&attr))
+	return libcCall(unsafe.Pointer(funcPC(pthread_create_trampoline)), unsafe.Pointer(&attr))
 }
 func pthread_create_trampoline()
 
 //go:nosplit
 //go:cgo_unsafe_args
 func raise(sig uint32) {
-	asmcgocall(unsafe.Pointer(funcPC(raise_trampoline)), unsafe.Pointer(&sig))
+	libcCall(unsafe.Pointer(funcPC(raise_trampoline)), unsafe.Pointer(&sig))
 }
 func raise_trampoline()
 
 //go:nosplit
 //go:cgo_unsafe_args
 func pthread_self() (t pthread) {
-	asmcgocall(unsafe.Pointer(funcPC(pthread_self_trampoline)), unsafe.Pointer(&t))
+	libcCall(unsafe.Pointer(funcPC(pthread_self_trampoline)), unsafe.Pointer(&t))
 	return
 }
 func pthread_self_trampoline()
@@ -61,7 +87,7 @@ func mmap(addr unsafe.Pointer, n uintptr, prot, flags, fd int32, off uint32) (un
 		ret1            unsafe.Pointer
 		ret2            int
 	}{addr, n, prot, flags, fd, off, nil, 0}
-	asmcgocall(unsafe.Pointer(funcPC(mmap_trampoline)), unsafe.Pointer(&args))
+	libcCall(unsafe.Pointer(funcPC(mmap_trampoline)), unsafe.Pointer(&args))
 	return args.ret1, args.ret2
 }
 func mmap_trampoline()
@@ -69,56 +95,56 @@ func mmap_trampoline()
 //go:nosplit
 //go:cgo_unsafe_args
 func munmap(addr unsafe.Pointer, n uintptr) {
-	asmcgocall(unsafe.Pointer(funcPC(munmap_trampoline)), unsafe.Pointer(&addr))
+	libcCall(unsafe.Pointer(funcPC(munmap_trampoline)), unsafe.Pointer(&addr))
 }
 func munmap_trampoline()
 
 //go:nosplit
 //go:cgo_unsafe_args
 func madvise(addr unsafe.Pointer, n uintptr, flags int32) {
-	asmcgocall(unsafe.Pointer(funcPC(madvise_trampoline)), unsafe.Pointer(&addr))
+	libcCall(unsafe.Pointer(funcPC(madvise_trampoline)), unsafe.Pointer(&addr))
 }
 func madvise_trampoline()
 
 //go:nosplit
 //go:cgo_unsafe_args
 func read(fd int32, p unsafe.Pointer, n int32) int32 {
-	return asmcgocall(unsafe.Pointer(funcPC(read_trampoline)), unsafe.Pointer(&fd))
+	return libcCall(unsafe.Pointer(funcPC(read_trampoline)), unsafe.Pointer(&fd))
 }
 func read_trampoline()
 
 //go:nosplit
 //go:cgo_unsafe_args
 func closefd(fd int32) int32 {
-	return asmcgocall(unsafe.Pointer(funcPC(close_trampoline)), unsafe.Pointer(&fd))
+	return libcCall(unsafe.Pointer(funcPC(close_trampoline)), unsafe.Pointer(&fd))
 }
 func close_trampoline()
 
 //go:nosplit
 //go:cgo_unsafe_args
 func exit(code int32) {
-	asmcgocall(unsafe.Pointer(funcPC(exit_trampoline)), unsafe.Pointer(&code))
+	libcCall(unsafe.Pointer(funcPC(exit_trampoline)), unsafe.Pointer(&code))
 }
 func exit_trampoline()
 
 //go:nosplit
 //go:cgo_unsafe_args
 func usleep(usec uint32) {
-	asmcgocall(unsafe.Pointer(funcPC(usleep_trampoline)), unsafe.Pointer(&usec))
+	libcCall(unsafe.Pointer(funcPC(usleep_trampoline)), unsafe.Pointer(&usec))
 }
 func usleep_trampoline()
 
 //go:nosplit
 //go:cgo_unsafe_args
 func write(fd uintptr, p unsafe.Pointer, n int32) int32 {
-	return asmcgocall(unsafe.Pointer(funcPC(write_trampoline)), unsafe.Pointer(&fd))
+	return libcCall(unsafe.Pointer(funcPC(write_trampoline)), unsafe.Pointer(&fd))
 }
 func write_trampoline()
 
 //go:nosplit
 //go:cgo_unsafe_args
 func open(name *byte, mode, perm int32) (ret int32) {
-	return asmcgocall(unsafe.Pointer(funcPC(open_trampoline)), unsafe.Pointer(&name))
+	return libcCall(unsafe.Pointer(funcPC(open_trampoline)), unsafe.Pointer(&name))
 }
 func open_trampoline()
 
@@ -129,7 +155,7 @@ func nanotime() int64 {
 		t            int64  // raw timer
 		numer, denom uint32 // conversion factors. nanoseconds = t * numer / denom.
 	}
-	asmcgocall(unsafe.Pointer(funcPC(nanotime_trampoline)), unsafe.Pointer(&r))
+	libcCall(unsafe.Pointer(funcPC(nanotime_trampoline)), unsafe.Pointer(&r))
 	// Note: Apple seems unconcerned about overflow here. See
 	// https://developer.apple.com/library/content/qa/qa1398/_index.html
 	// Note also, numer == denom == 1 is common.