On amd64, arm64 and i386, we have the possibility to switch between TLS
areas in userspace. The nice thing about this is that it makes it easier
to do light-weight threading, if we ever feel like doing that. On armv6,
let's go into the same direction by making it possible to safely use the
TPIDRURW register, which is intended for this purpose.
Clean up the ARMv6 code to remove md_tp entirely. Simply add a dedicated
field to the PCB to hold the value of TPIDRURW across context switches,
like we do for any other register. As userspace currently uses the
read-only TPIDRURO register, simply ensure that we keep both values in
sync where possible. The system calls for modifying the read-only
register will simply write the intended value into both registers, so
that it lazily ends up in the PCB during the next context switch.
Reviewed by: https://reviews.freebsd.org/D7951
Approved by: andrew
Reviewed by: imp
Differential Revision: https://reviews.freebsd.org/D7951
Previous code supported only "continuous" code without any kind of
branch instructions. To change that, new function was implemented
which parses current instruction and returns an addres where
the jump might happen (alternative addr).
mdthread structure was extended to support two breakpoints
(one directly below current instruction and the second placed
at the alternative location).
One of them must trigger regardless the instruction has or has not been
executed due to condition field.
Upon cleanup, both software breakpoints are removed.
This implementation parses only the most common instructions
that are present in the code (like 99.99% of all), but there
is a chance there are some left, not covered by the parsing routine.
Parsing is done only for 32-bit instruction, no Thumb nor Thumb-2
support is provided.
Reviewed by: kib
Submitted by: Wojciech Macek <wma@semihalf.com>
Obtained from: Semihalf
Sponsored by: Juniper Networks Inc.
Differential Revision: https://reviews.freebsd.org/D4021
1. Align to a 64-bit address so 64-bit data will be correctly aligned.
2. Add a comment explaining why.
3. Remove an unneeded value from the struct.
This fixes an issue where the struct may not be correctly aligned on the
stack in the syscall function. This may lead to accesing a 64-bit value
at a non 64-bit. This will raise an exception and panic the kernel.
We have been lucky where on arm and armv6 both clang and gcc correctly
align the data, even without us asking to, however, on armeb with clang to
not be the case. This tells the compiler we really do need this to be
aligned.
Reported and tested by: jmg (on armeb with clang)
MFC after: 1 Week [1, 2]
mostly paves the way for the new pmap code, and shouldn't result in any
noticible behavior differences.
Submitted by: Svatopluk Kraus <onwahe@gmail.com>,
Michal Meloun <meloun@miracle.cz
critical_enter() and critical_exit() are now solely a mechanism for
deferring kernel preemptions. They no longer have any affect on
interrupts. This means that standalone critical sections are now very
cheap as they are simply unlocked integer increments and decrements for the
common case.
Spin mutexes now use a separate KPI implemented in MD code: spinlock_enter()
and spinlock_exit(). This KPI is responsible for providing whatever MD
guarantees are needed to ensure that a thread holding a spin lock won't
be preempted by any other code that will try to lock the same lock. For
now all archs continue to block interrupts in a "spinlock section" as they
did formerly in all critical sections. Note that I've also taken this
opportunity to push a few things into MD code rather than MI. For example,
critical_fork_exit() no longer exists. Instead, MD code ensures that new
threads have the correct state when they are created. Also, we no longer
try to fixup the idlethreads for APs in MI code. Instead, each arch sets
the initial curthread and adjusts the state of the idle thread it borrows
in order to perform the initial context switch.
This change is largely a big NOP, but the cleaner separation it provides
will allow for more efficient alternative locking schemes in other parts
of the kernel (bare critical sections rather than per-CPU spin mutexes
for per-CPU data for example).
Reviewed by: grehan, cognet, arch@, others
Tested on: i386, alpha, sparc64, powerpc, arm, possibly more
It only supports sa1110 (on simics) right now, but xscale support should come
soon.
Some of the initial work has been provided by :
Stephane Potvin <sepotvin at videotron.ca>
Most of this comes from NetBSD.
