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