Re: erlang -> asmjit -> mremap questions/bugs

[Thomas Klausner <wiz%NetBSD.org@localhost>]

On Wed, Mar 01, 2023 at 05:48:08PM +0300, Valeriy E. Ushakov wrote:
> On Wed, Mar 01, 2023 at 15:29:27 +0100, Thomas Klausner wrote:
> 
> > It seems the problem is that mmap() in the mremap(2) man page example
> > (which was used to implement the asmjit version) is not using
> > MAP_SHARED.
> > 
> > - I'd like to add MAP_SHARED in the mmap() call in the mremap(2) man
> >   page example. Is that fine?
> 
> Not really.  There are no other processes involved in the example, so
> MAP_SHARED makes no sense.
> 
> 
> > - Reading mmap(2) it seems that one of MAP_SHARED or MAP_PRIVATE is
> >   required, but there is no error if none is provided. Should we change
> >   mmap() to return an error in that case?
> 
> sys/kern/vfs_vnops.c:
> 
>     /*
>      * Old programs may not select a specific sharing type, so
>      * default to an appropriate one.
>      */

So this looks like it would default to MAP_PRIVATE.

> > - Why does MAP_PRIVATE (instead of MAP_SHARED) not work?
> 
> Are there multiple processes involved in the erlang case?

I don't think so - it's a VM running a program. Multiple threads
perhaps. I'll ask.
 Thomas