riscv: fix AMO, LR and SC instructions

(1) Atomic Memory Operation (AMO)

This patch changes how RISC-V AMO instructions are implemented. For each
AMO, instead of issuing a locking load and an unlocking store request to
downstream memory system, this patch issues a single memory request that
contains a corresponding AtomicOpFunctor to the memory system. Once the
memory system receives the request, the atomic operation is executed in
one single step.

This patch also changes how AMO instructions handle acquire and release
flags in AMOs (e.g., amoadd.aq and amoadd.rl). If an AMO is associated
with an acquire flag, a memory fence is inserted after the AMO completes
as a micro-op. If an AMO is associated with a release flag, another
memory fence is inserted before the AMO executes. If both flags are
specified, the AMO is broken down into a sequence of 3 micro-ops:
mem fence -> atomic RMW -> mem fence. This change makes this AMO
implementation comply to the release consistency model.

(2) Load-Reserved (LR) and Store-Conditional (SC)

Addresses locked by LR instructions are tracked in a stack data
structure. LR instruction pushes its target address to the stack, and SC
instruction pops the top address from the stack. As specified by RISC-V
ISA, a SC fails if its target address does not match with the most recent
LR.

Previously, there was a single stack for all hardware thread contexts.
A shared stack between thread contexts can lead to a infinite sequence
of failed SCs if LRs from other threads keep pushing new addresses to
this stack.

This patch gives each context its private stack to address the problem.

This patch also adds extra memory fence micro-ops to lr/sc to guarantee
a correct execution order of memory instructions with respect to release
consistency model.

Change-Id: I1e95900367c89dd866ba872a5203f63359ac51ae
Reviewed-on: https://gem5-review.googlesource.com/c/8189
Reviewed-by: Alec Roelke <ar4jc@virginia.edu>
Maintainer: Alec Roelke <ar4jc@virginia.edu>

arch-riscv: Add support for trap value register

RISC-V has a set of CSRs that contain information about a trap that was
taken into each privilegel level, such as illegal instruction bytes or
faulting address. This patch adds that register, modifies existing
faults to make use of it, and adds a new fault for future use with
handling page faults and bad addresses.

Change-Id: I3004bd7b907e7dc75e5f1a8452a1d74796a7a551
Reviewed-on: https://gem5-review.googlesource.com/11135
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Alec Roelke <alec.roelke@gmail.com>

arch-riscv: Update CSR implementations

This patch updates the CSRs to match the RISC-V privileged specification
version 1.10. As interrupts, faults, and privilege levels are not yet
supported, there are no meaninful side effects that are implemented.
Performance counters are also not yet implemented, as they do not have
specifications. Currently they act as cycle counters.

Note that this implementation trusts software to use the registers
properly. Access protection, readability, and writeability of registers
based on privilege will come in a future patch.

Change-Id: I1de89bdbe369b5027911b2e6bc0425d3acaa708a
Reviewed-on: https://gem5-review.googlesource.com/7441
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Alec Roelke <ar4jc@virginia.edu>

arch: Fix all override related warnings.

Clang has started(?) reporting override related warnings, something gcc
apparently did before, but was disabled in the SConstruct. Rather than
disable the warnings in for clang as well, this change fixes the
warnings. A future change will re-enable the warnings for gcc.

Change-Id: I3cc79e45749b2ae0f9bebb1acadc56a3d3a942da
Reviewed-on: https://gem5-review.googlesource.com/9343
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>

arch: Add a virtual asBytes function to the StaticInst class.

This function takes a pointer to a buffer and the current size of the
buffer as a pass by reference argument. If the size of the buffer is
sufficient, the function stores a binary representation of itself
(generally the ISA defined instruction encoding) in the buffer, and
sets the size argument to how much space it used. This could be used
by ISAs which have two instruction sizes (ARM and thumb, for example).
If the buffer size isn't sufficient, then the size parameter should be
set to what size is required, and then the function should return
without modifying the buffer.

The buffer itself should be aligned to the same standard as memory
returned by new, specifically "The pointer returned shall be suitably
aligned so that it can be converted to a pointer of any complete object
type and then used to access the object or array in the storage
allocated...". This will avoid having to memcpy buffers to avoid
unaligned accesses.

To standardize the representation of the data, it should be stored in
the buffer as little endian. Since most hosts (including ARM and x86
hosts) will be little endian, this will almost always be a no-op.

Change-Id: I2f31aa0b4f9c0126b44f47a881c2901243279bd6
Reviewed-on: https://gem5-review.googlesource.com/7562
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>

riscv: Add overrides to various StaticInst methods.

This makes riscv compile with the version of clang(++) I have on my
workstation.

Change-Id: I0478616810fbc8a715fd61323b7e0f73676c8328
Reviewed-on: https://gem5-review.googlesource.com/7643
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>

arch-riscv: Don't crash when printing unknown CSRs

This patch fixes a potential crash if an unnamed CSR is accessed and
debug flags are enabled that print disassembly. Unknown CSRs will be
identified as "??" followed by the address that was used.

Change-Id: If5ac57f1422bd59c72a1a06206fa9d9dc05d21ef
Reviewed-on: https://gem5-review.googlesource.com/7321
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Alec Roelke <ar4jc@virginia.edu>

arch-riscv: Move compressed ops out of ISA

This patch moves static portions of the compressed instruction
definitions out of the ISA generated code.

Change-Id: I61daae8b8c03a9e0f012790a132aa4d34a6ec296
Reviewed-on: https://gem5-review.googlesource.com/6026
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Alec Roelke <ar4jc@virginia.edu>

arch-riscv: Add missing license paragraphs

Some of the files in earlier patches rearranging instruction definitions
were missing copyright and license information. This patch adds them.

Change-Id: I2ac4910a415de6032fc0b7d4422904c682e0ad87
Reviewed-on: https://gem5-review.googlesource.com/6183
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

arch-riscv: Remove static parts of AMOs out of ISA

This patch removes the static parts of the RISC-V atomic memory
instructions out of the ISA generated code and into arch/riscv/insts. It
also makes the LR and SC instructions subclasses of MemInst from
arch/riscv/insts/mem.hh.

Change-Id: I6591f3d171045c4f1b457eb1264bbb7bd62b3e51
Reviewed-on: https://gem5-review.googlesource.com/6025
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Alec Roelke <ar4jc@virginia.edu>

arch-riscv: Move parts of mem insts out of ISA

This patch moves static portions of the memory instructions out of the
ISA generated code and puts them into arch/riscv/insts. It also
simplifies the definitions of load and store instructions by giving
them a common base class.

Change-Id: Ic6930cbfc6bb02e4b3477521e57b093eac0c8803
Reviewed-on: https://gem5-review.googlesource.com/6024
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Alec Roelke <ar4jc@virginia.edu>

arch-riscv: Move unknown out of ISA description

This patch removes the Unknown instruction type out of the ISA generated
code and puts it into arch/riscv/insts. Since there isn't any dynamic
behavior to it, all that's left behind is a template for creating a new
Unknown instruction.

Change-Id: If7c3258a24ecadd3e00ab74586e1740e14f028db
Reviewed-on: https://gem5-review.googlesource.com/6023
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Alec Roelke <ar4jc@virginia.edu>

arch-riscv: Move standard ops out of ISA

This patch removes static portions of the standard instruction types
from the generated ISA code and puts them into arch/riscv/insts. Some
dynamically-generated content is left behind for each individual
instruction's implementation. Also, BranchOp is removed due to its
similarity with ImmOp and ImmOp and UImmOp are joined into a single
templated class, ImmOp<T>.

Change-Id: I1bf47c8b8a92a5be74a50909fcc51d8551185a2a
Reviewed-on: https://gem5-review.googlesource.com/6022
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Alec Roelke <ar4jc@virginia.edu>

arch-riscv: Move static_inst into a directory

This patch creates an "insts" directory in src/arch/riscv to store
static portions of instruction definitions that aren't part of the code
generated by the ISA description. It serves as a starting point for
future patches to simplify the ISA description.

Change-Id: I6700522143f6fa6c9b18a30e1fbdc8f80cdc7afa
Reviewed-on: https://gem5-review.googlesource.com/6021
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Alec Roelke <ar4jc@virginia.edu>