svn commit: r337127 - head/sys/riscv/riscv

[Konstantin Belousov]

On Thu, Aug 02, 2018 at 08:16:59AM -0700, John Baldwin wrote:
> On 8/2/18 5:13 AM, Ruslan Bukin wrote:
> > Author: br
> > Date: Thu Aug  2 12:13:52 2018
> > New Revision: 337127
> > URL: https://svnweb.freebsd.org/changeset/base/337127
> > 
> > Log:
> >   Don't overwrite tp in set_mcontext().
> >   
> >   This makes libthr/swapcontext_test:swapcontext1 happy.
> >   
> >   Sponsored by:	DARPA, AFRL
> 
> This seems a bit odd.  Is get_mcontext() not setting gp_tp correctly, or is
> makecontext() not preserving it perhaps?
> 
> In general I feel like we should be saving/restoring 'tp' in the trapframe
> on kernel entry/exit like other GPRs instead of in the pcb and then
> including it in 'struct reg'.  This makes it possible for debuggers to
> handle TLS variables more sanely (and in general we need to fix the various
> struct reg in FreeBSD architectures to include TLS registers when possible,
> such as adding fs_base and gs_base on x86).  It would be nice if RISC-V
> started off on the correct foot here.

I wanted to do this on x86, but I gave up due to the ABI issues.
When FSGSBASE instructions are supported on amd64, we save base
on context switch and restore on return to usermode.