Re: RFC: userspace exception fixups

[Rich Felker]

On Thu, Nov 01, 2018 at 12:10:35PM -0700, Linus Torvalds wrote:
> On Thu, Nov 1, 2018 at 11:52 AM Rich Felker <dalias@xxxxxxxx> wrote:
> >
> > There's no need to chain if the handler is specific to the context
> > where the fault happens. You just replace the handler with the one
> > relevant to the code you're about to run before you run it.
> 
> That's much too expensive to do as a system call.

See my other emails in this thread. You would register the *address*
(in TLS) of a function pointer object pointing to the handler, rather
than the function address of the handler. Then switching handler is
just a single store in userspace, no syscalls involved.

Rich