[PATCH] Workaround a FreeBSD ptrace() bug with clearing thread events.

[Maciej W. Rozycki]

On Fri, 2 Mar 2018, John Baldwin wrote:

> >  Is the one-way compatibility enforced though, by a system library runtime 
> > or the kernel somehow, by refusing to run a binary built for a kernel that 
> > is newer than one currently in charge of the system?  Otherwise the rule 
> > would be quite fragile and error prone, asking for extra care to be taken 
> > by the user.
> 
> It is enforced in some ways but not others.  Kernel modules do depend on a
> version number in such a way that attempting to load a newer kernel module
> on an older kernel will fail.  However, the general policy of only supporting
> one-way compatibility is well-known among the FreeBSD userbase (for example,
> the instructions for upgrading a system from source require booting into a
> new kernel before installing the matching userland binaries).

 That all sounds right, however does not really address my concern where a 
user *unknowingly* tries a program binary that has been compiled for a 
newer kernel version and then faces all kinds of issues.  This is bound to 
happen sooner or later for someone, the Murphy's law guarantees it.

  Maciej