On Sat, Mar 13, 2021 at 10:26 PM rmfr wrote:
>
> Maybe the reason for such a strict rule on using cgo is just to take
> precautions if our GC moves object in the future? And at that time, the
> syscall implementation must be rewritten to add some codes to pinning the
> objects used by each syscall from being moved. Am I correct?
Yes, exactly. There are special rules for syscall, and the Go project
promises that syscall will keep working, including pinning pointers,
and internal pointers, that are passed to syscalls.
Ian
> On Sunday, March 14, 2021 at 2:11:18 PM UTC+8 rmfr wrote:
>>
>> I am watching the implementation of syscall `writev` from
>> [here](https://github.com/golang/sys/blob/bd2e13477e9c63125302cd9da2d61879c6aa1721/unix/zsyscall_linux.go#L1641),
>> and comparing it with the
>> [proposal](https://github.com/golang/proposal/blob/master/design/12416-cgo-pointers.md)
>> of cgo. I found the rule applies on cgo and syscall is inconsistent.
>>
>> If the object could be moved during GC, then the code to implement `writev`
>> is incorrect. Because GC could happen during the syscall and the byte slices
>> kernel is using has been moved! :-(
>>
>> If the object may not be moved during GC, then the code to implement syscall
>> `writev` is correct. But from the perspective of go runtime, cgo is just a
>> kind of special "syscall", then the rule applies to cgo now is far too
>> strict -- you simply couldn't call a C API like `writev` which takes array
>> of byte slices as input arg (because the rule applies on cgo now only allow
>> one input arg contains at most one go pointer).
>>
>> Maybe I have missed something, please correct me. Thanks a lot for your
>> patient and kindness :-)
>
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