riscv: Get rid of some ISA specific register types.

Change-Id: Ie812cf1d42536094273ba2ec731c16cca38db100
Reviewed-on: https://gem5-review.googlesource.com/c/14466
Reviewed-by: Alec Roelke <alec.roelke@gmail.com>
Maintainer: Alec Roelke <alec.roelke@gmail.com>

arch-riscv: Add interrupt handling

Implement the Interrupts SimObject for RISC-V. This basically just
handles setting and getting the values of the interrupt-pending and
interrupt-enable CSRs according to the privileged ISA reference chapter
3.1.14. Note that it does NOT implement the PLIC as defined in chapter
7, as that is used for handling external interrupts which are defined
based on peripherals that are available.

Change-Id: Ia1321430f870ff5a3950217266fde0511332485b
Reviewed-on: https://gem5-review.googlesource.com/c/14377
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

arch-riscv: Fix reset function and style

In addition to fixing some style issues with resetting, this patch fixes
what happens on reset. The RISC-V privileged ISA reference manual says
that,
on reset:
1. Privilege mode is set to M
2. mstatus.mie <- 0; mstatus.mprv <- 0
3. PC <- reset vector
4. mcause <- reset cause (0 if there is no distinguishing causes)
5. Everything else is undefined
Because of 5, everything else will be left alone

Change-Id: I81bdf7a88b08874e3c3d5fc6c7f3ca2d796496b8
Reviewed-on: https://gem5-review.googlesource.com/c/14376
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

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: Add support for fault handling

This patch adds support for handling RISC-V faults, including tracking
current and previous execution privilege, correctly switching to
the privilege mode specified by CSRs, and setting/storing the PC. It
also includes changes introduced by patch #9821, which disables
interrupts during handling of a fault.

Change-Id: Ie9c0f29719620c20783540d3bdb2db44f6114fc9
Reviewed-on: https://gem5-review.googlesource.com/9161
Maintainer: Alec Roelke <ar4jc@virginia.edu>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

arch-riscv: enable rudimentary fs simulation

These changes enable a simple binary to be simulated in full system mode.
Additionally, a new fault was implemented.
It is executed once the CPU is initialized.
This fault clears all interrupts and sets the pc to a reset vector.

Change-Id: I50cfac91a61ba39a6ef3d38caca8794073887c88
Reviewed-on: https://gem5-review.googlesource.com/9061
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>

riscv: Fix bugs with RISC-V decoder and detailed CPUs

This patch fixes some bugs that were missed with the changes to the
decoder that enabled compatibility with compressed instructions. In
order to accommodate speculation with variable instruction widths, a few
assertions in decoder had to be changed to returning faults as the
specification describes should normally happen. The rest of these
assertions will be changed in a later patch.

[Remove commented-out debugging line and add clarifying comment to
registerName in utility.hh.]

Change-Id: I3f333008430d4a905cb59547a3513f5149b43b95
Reviewed-on: https://gem5-review.googlesource.com/4041
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Alec Roelke <ar4jc@virginia.edu>

syscall_emul: [patch 13/22] add system call retry capability

This changeset adds functionality that allows system calls to retry without
affecting thread context state such as the program counter or register values
for the associated thread context (when system calls return with a retry
fault).

This functionality is needed to solve problems with blocking system calls
in multi-process or multi-threaded simulations where information is passed
between processes/threads. Blocking system calls can cause deadlock because
the simulator itself is single threaded. There is only a single thread
servicing the event queue which can cause deadlock if the thread hits a
blocking system call instruction.

To illustrate the problem, consider two processes using the producer/consumer
sharing model. The processes can use file descriptors and the read and write
calls to pass information to one another. If the consumer calls the blocking
read system call before the producer has produced anything, the call will
block the event queue (while executing the system call instruction) and
deadlock the simulation.

The solution implemented in this changeset is to recognize that the system
calls will block and then generate a special retry fault. The fault will
be sent back up through the function call chain until it is exposed to the
cpu model's pipeline where the fault becomes visible. The fault will trigger
the cpu model to replay the instruction at a future tick where the call has
a chance to succeed without actually going into a blocking state.

In subsequent patches, we recognize that a syscall will block by calling a
non-blocking poll (from inside the system call implementation) and checking
for events. When events show up during the poll, it signifies that the call
would not have blocked and the syscall is allowed to proceed (calling an
underlying host system call if necessary). If no events are returned from the
poll, we generate the fault and try the instruction for the thread context
at a distant tick. Note that retrying every tick is not efficient.

As an aside, the simulator has some multi-threading support for the event
queue, but it is not used by default and needs work. Even if the event queue
was completely multi-threaded, meaning that there is a hardware thread on
the host servicing a single simulator thread contexts with a 1:1 mapping
between them, it's still possible to run into deadlock due to the event queue
barriers on quantum boundaries. The solution of replaying at a later tick
is the simplest solution and solves the problem generally.

riscv: [Patch 3/5] Added RISCV floating point extensions RV64FD

Third of five patches adding RISC-V to GEM5. This patch adds the RV64FD
extensions, which include single- and double-precision floating point
instructions.

Patch 1 introduced RISC-V and implemented the base instruction set, RV64I
and patch 2 implemented the integer multiply extension, RV64M.

Patch 4 will implement the atomic memory instructions, RV64A, and patch
5 will add support for timing, minor, and detailed CPU models that is
missing from the first four patches.

[Fixed exception handling in floating-point instructions to conform better
to IEEE-754 2008 standard and behavior of the Chisel-generated RISC-V
simulator.]
[Fixed style errors in decoder.isa.]
[Fixed some fuzz caused by modifying a previous patch.]
Signed-off by: Alec Roelke

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

arch: [Patch 1/5] Added RISC-V base instruction set RV64I

First of five patches adding RISC-V to GEM5. This patch introduces the
base 64-bit ISA (RV64I) in src/arch/riscv for use with syscall emulation.
The multiply, floating point, and atomic memory instructions will be added
in additional patches, as well as support for more detailed CPU models.
The loader is also modified to be able to parse RISC-V ELF files, and a
"Hello world\!" example for RISC-V is added to test-progs.

Patch 2 will implement the multiply extension, RV64M; patch 3 will implement
the floating point (single- and double-precision) extensions, RV64FD;
patch 4 will implement the atomic memory instructions, RV64A, and patch 5
will add support for timing, minor, and detailed CPU models that is missing
from the first four patches (such as handling locked memory).

[Removed several unused parameters and imports from RiscvInterrupts.py,
RiscvISA.py, and RiscvSystem.py.]
[Fixed copyright information in RISC-V files copied from elsewhere that had
ARM licenses attached.]
[Reorganized instruction definitions in decoder.isa so that they are sorted
by opcode in preparation for the addition of ISA extensions M, A, F, D.]
[Fixed formatting of several files, removed some variables and
instructions that were missed when moving them to other patches, fixed
RISC-V Foundation copyright attribution, and fixed history of files
copied from other architectures using hg copy.]
[Fixed indentation of switch cases in isa.cc.]
[Reorganized syscall descriptions in linux/process.cc to remove large
number of repeated unimplemented system calls and added implmementations
to functions that have received them since it process.cc was first
created.]
[Fixed spacing for some copyright attributions.]
[Replaced the rest of the file copies using hg copy.]
[Fixed style check errors and corrected unaligned memory accesses.]
[Fix some minor formatting mistakes.]
Signed-off by: Alec Roelke

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