Thanks. I did misunderstand the 'exception'. 在2021年4月18日星期日 UTC+8 下午5:19:22<axel.wa...@googlemail.com> 写道：
> Not "raise an exception", "make an exception". Go doesn't have exceptions, > so the word "exception" here means "not do something you'd otherwise do" - > namely "complain about the conversion of a uintptr to an unsafe.Pointer" :) > > The exact rules for converting to and from unsafe.Pointer are here: > https://golang.org/pkg/unsafe/#Pointer > Rule 5 is the relevant one - so, yes, this is safe. > > On Sun, Apr 18, 2021 at 1:46 AM Name No <zylth...@gmail.com> wrote: > >> >> reflect.Value.UnsafeAddr has the commence attached like that: >> >> //go:nocheckptr >> // This prevents inlining Value.UnsafeAddr when -d=checkptr is enabled, >> // which ensures cmd/compile can recognize unsafe.Pointer(v.UnsafeAddr()) >> // and make an exception. >> >> Seems it is saying unsafe.Pointer(reflect.Value.UnsafeAddr()) is >> dangerous that go:nocheckptr can disable UnsafeAddr from inline, so >> cmd/compile can detect it is a function call and raise an exception. >> >> But indeed, the following code will not raise any exception at ptr := >> unsafe.Pointer(rf.UnsafeAddr()). >> It indicates that unsafe.Pointer(rf.UnsafeAddr()) is safe. >> >> Anybody can help to explain this? >> >> go run -race -gcflags=all=-d=checkptr c.go >> package main >> >> import ( >> "reflect" >> "unsafe" >> "fmt" >> ) >> >> func main() { >> var s = struct{ foo int }{100} >> >> rs := reflect.ValueOf(&s).Elem() >> rf := rs.Field(0) >> >> ptr := unsafe.Pointer(rf.UnsafeAddr()) >> >> x := rf.UnsafeAddr() >> ptr = unsafe.Pointer(x) >> fmt.Println(ptr) >> } >> >> -- >> You received this message because you are subscribed to the Google Groups >> "golang-nuts" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to golang-nuts...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/golang-nuts/14da5c55-9137-46bc-90e1-b51b8ef6553bn%40googlegroups.com >> >> <https://groups.google.com/d/msgid/golang-nuts/14da5c55-9137-46bc-90e1-b51b8ef6553bn%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/c80a7ef6-eb49-41be-b40d-32f26c5e9b3an%40googlegroups.com.
