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 <[email protected]> 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 [email protected]. > 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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAEkBMfF4HKpwSf-ET-gFqQxGx7oZjy0NY4i%3D-xs1xRVYvuEuoA%40mail.gmail.com.
