On Wed, Jun 10, 2020 at 4:15 AM Viktor Kojouharov <vkojouha...@gmail.com> wrote:
> Thanks Ian. Adding to that allocation to cover the element size did the > trick. Out of curiosity, the momery allocated by mallocgc is still tracked > by the gc, right? > A brief look at the code seems to indicate that this is the case, but I > don't know how the gc works. > Correct. > > On Monday, June 8, 2020 at 9:41:21 PM UTC+3, Ian Lance Taylor wrote: >> >> On Mon, Jun 8, 2020 at 10:44 AM Viktor Kojouharov <vkojo...@gmail.com> >> wrote: >> > >> > The full code can be seen in this diff: >> > >> > >> https://github.com/urandom/go/commit/d10ccdd907dac690bfcb31df1115ce1508775458 >> > >> > The just of it is, I've added an extra field to a struct (the chan) of >> type unsafe.Pointer. The value is then copied (allegedly) to a target >> pointer in chanrecv using typedmemmove. The types of both pointers are the >> same, as defined by the chan's elemtype >> >> I only took a quick look, but it looks like you have added a pointer >> field to hchan, and presumably the garbage collector needs to know >> about that pointer. If you look at makechan in runtime/chan.go, you >> will see that a channel whose element type does not contain any >> pointers is allocated in such a way that the garbage collector never >> looks at it. That will break with your new pointer, as the collector >> can collect the value to which the new pointer points without changing >> that pointer. >> >> Ian >> >> >> >> > On Monday, June 8, 2020 at 3:12:18 AM UTC+3, keith....@gmail.com >> wrote: >> >> >> >> Showing us some code would really help. It's hard to understand what >> you are doing from this brief description. Also, where does the SIGBUS >> occur? What pc, and what address? >> >> >> >> What types are you passing as the first argument to typedmemmove? >> Where did you get them from? >> >> >> >> This is a fine question for golang-dev, but don't expect a whole lot >> of help - reaching into the runtime to call typedmemmove is very >> unsupported. >> >> >> >> On Sunday, June 7, 2020 at 10:02:21 AM UTC-7, Michael Jones wrote: >> >>> >> >>> Thank you. I now officially know that I don’t understand. Sorry. >> >>> >> >>> On Sun, Jun 7, 2020 at 7:54 AM Viktor Kojouharov <vkojo...@gmail.com> >> wrote: >> >>>> >> >>>> The pointer is being copied via typedmemmove, which itself calls >> memmove, which, according to its documentation, copies bytes from the >> source to the destination. Not sure why that would be impossible, >> considering it does work for some code (the source pointer preserves its >> data) >> >>>> >> >>>> Not sure what you mean by "copied via unsafe". Also, the source >> pointer never goes out of scope. It's part of a struct that is passed to >> the function that calls typedmemmove, and its lifetime is more or less >> static. So while the destination pointers go out of scope, the source one >> never does. >> >>>> >> >>>> >> >>>> On Sunday, June 7, 2020 at 4:45:40 PM UTC+3, Michael Jones wrote: >> >>>>> >> >>>>> Do you mean that you have a problem with the value of the pointer? >> That is "copying the pointer." This seems impossible. >> >>>>> >> >>>>> Attempting to access through a pointer copied via unsafe is >> (generally) inviting doom, and seems highly possible. The instant the last >> pointer to that data goes out of scope the address range occupied by the >> formerly pointed to items is formally inaccessible. Using unsafe to keep a >> shadow copy of the address and then poking around is quite likely to fail, >> and even when it does not, it is quite likely to be meaningless. (random >> data from some other use). >> >>>>> >> >>>>> If I misunderstood, please forgive me. >> >>>>> >> >>>>> On Sun, Jun 7, 2020 at 6:15 AM Viktor Kojouharov < >> vkojo...@gmail.com> wrote: >> >>>>>> >> >>>>>> p.s. should such questions be posted in golang-dev, since it deals >> with runtime internals? >> >>>>>> >> >>>>>> -- >> >>>>>> 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 golan...@googlegroups.com. >> >>>>>> To view this discussion on the web visit >> https://groups.google.com/d/msgid/golang-nuts/71d7fb5c-3ef5-4611-b9ce-299f7b90945eo%40googlegroups.com. >> >> >>>>> >> >>>>> >> >>>>> >> >>>>> -- >> >>>>> Michael T. Jones >> >>>>> michae...@gmail.com >> >>>> >> >>>> -- >> >>>> 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 golan...@googlegroups.com. >> >>>> To view this discussion on the web visit >> https://groups.google.com/d/msgid/golang-nuts/fa18bf7e-8965-4917-9d81-00a8f43289c3o%40googlegroups.com. >> >> >>> >> >>> -- >> >>> Michael T. Jones >> >>> michae...@gmail.com >> > >> > -- >> > 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 golan...@googlegroups.com. >> > To view this discussion on the web visit >> https://groups.google.com/d/msgid/golang-nuts/aa037e65-0e2a-47d6-b35c-8e80fc3a8000o%40googlegroups.com. >> >> > -- > You received this message because you are subscribed to a topic in the > Google Groups "golang-nuts" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/golang-nuts/V2abC-HQvYk/unsubscribe. > To unsubscribe from this group and all its topics, 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/01e4daa4-568d-4d56-9691-66272e908a3do%40googlegroups.com > <https://groups.google.com/d/msgid/golang-nuts/01e4daa4-568d-4d56-9691-66272e908a3do%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. 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