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>

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>

cpu,alpha,mips,power,riscv,sparc: Get rid of eaComp and memAccInst.

Neither of these were used, particularly memAccInst.

Change-Id: I4ac9e44cf624e5de42519d586d7b699f08a2cdfc
Reviewed-on: https://gem5-review.googlesource.com/6601
Maintainer: Gabe Black <gabeblack@google.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.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>

alpha,arm,mips,power,riscv,sparc,x86: Merge exec decl templates.

In the ISA instruction definitions, some classes were declared with
execute, etc., functions outside of the main template because they
had CPU specific signatures and would need to be duplicated with
each CPU plugged into them. Now that the instructions always just
use an ExecContext, there's no reason for those templates to be
separate. This change folds those templates together.

Change-Id: I13bda247d3d1cc07c0ea06968e48aa5b4aace7fa
Reviewed-on: https://gem5-review.googlesource.com/5401
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Alec Roelke <ar4jc@virginia.edu>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

alpha,arm,mips,power,riscv,sparc,x86,isa: De-specialize ExecContexts.

The ISA parser used to generate different copies of exec functions
for each exec context class a particular CPU wanted to use. That's
since been changed so that those functions take a pointer to the base
ExecContext, so the code which would generate those extra functions
can be removed, and some functions which used to be templated on an
ExecContext subclass can be untemplated, or minimally less templated.

Now that some functions aren't going to be instantiated multiple times
with different signatures, there are also opportunities to collapse
templates and make many instruction definitions simpler within the
parser. Since those changes will be less mechanical, they're left for
later changes and will probably be done in smaller increments.

Change-Id: I0015307bb02dfb9c60380b56d2a820f12169ebea
Reviewed-on: https://gem5-review.googlesource.com/5381
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

arch-riscv: Restructure ISA description

This patch restructures the RISC-V ISA description to use fewer classes
and improve its ability to be extended with nonstandard extensions in
the future. It also cleans up the disassembly for some of the CSR and
system instructions by removing source and destination registers for
instructions that don't have any.

[Fix class UImmOp to have an "imm" member rather than "uimm".]
[Update disassembly generation for new RegId class.]

Change-Id: Iec1c782020126e5e8e73460b84e31c7b5a5971d9
Reviewed-on: https://gem5-review.googlesource.com/3800
Maintainer: Alec Roelke <ar4jc@virginia.edu>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

riscv: fix Linux problems with LR and SC ops

Some of the functions in the Linux toolchain that allocate memory make
use of paired LR and SC instructions, which didn't work properly for
that toolchain. This patch fixes that so attempting to use those
functions doesn't cause an endless loop of failed SC instructions.

Change-Id: If27696323dd6229a0277818e3744fbdf7180fca7
Reviewed-on: https://gem5-review.googlesource.com/2340
Maintainer: Alec Roelke <ar4jc@virginia.edu>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

riscv: [Patch 4/5] Added RISC-V atomic memory extension RV64A

Fourth of five patches adding RISC-V to GEM5. This patch adds the RV64A
extension, which includes atomic memory instructions. These instructions
atomically read a value from memory, modify it with a value contained in a
source register, and store the original memory value in the destination
register and modified value back into memory. Because this requires two
memory accesses and GEM5 does not support two timing memory accesses in
a single instruction, each of these instructions is split into two micro-
ops: A "load" micro-op, which reads the memory, and a "store" micro-op,
which modifies and writes it back. Each atomic memory instruction also has
two bits that acquire and release a lock on its memory location.
Additionally, there are atomic load and store instructions that only either
load or store, but not both, and can acquire or release memory locks.

Note that because the current implementation of RISC-V only supports one
core and one thread, it doesn't make sense to make use of AMO instructions.
However, they do form a standard extension of the RISC-V ISA, so they are
included mostly as a placeholder for when multithreaded execution is
implemented. As a result, any tests for their correctness in a future
patch may be abbreviated.

Patch 1 introduced RISC-V and implemented the base instruction set, RV64I;
patch 2 implemented the integer multiply extension, RV64M; and patch 3
implemented the single- and double-precision floating point extensions,
RV64FD.

Patch 5 will add support for timing, minor, and detailed CPU models that
isn't present in patches 1-4.

[Added missing file amo.isa]
[Replaced information removed from initial patch that was missed during
division into multiple patches.]
[Fixed some minor formatting issues.]
[Fixed oversight where LR and SC didn't have both AQ and RL flags.]
Signed-off by: Alec Roelke

Signed-off by: Jason Lowe-Power <jason@lowepower.com>