Add htif_t tohost/fromhost accessors

Signed-off-by: Jerry Zhao <jerryz123@berkeley.edu>

Add more hint when searched path is wrong

Delete the old branch and pull a new one, because of a wrong force push. Git is not as easy as I think.

Signed-off-by: gr816ox <50945677+gr816ox@users.noreply.github.com>

Lift artificial limit of 191 extensions; simplify isa_parser_t::extension_enabled

Now that we guarantee that max_isa and extension_table are synchronized,
we only need to check the latter.

This fixes a bug where --isa=rv64imafdc would fail to set
extension_table['F'] because of the ad hoc manner in which we were
synchronizing max_isa and extension_table.

We know its size at compile time.

Add new accessors that accept the isa_extension_t enum.

Retain the original ones that accept unsigned char to avoid churn.

Add legalize_timing() for tdata1.timing

Since this method does not use 'this', we turn this method into static.

Since this method no longer use 'this', we turn this method into static.

avoid breaking functionality by reordering statements in tdata1.write()

As recommended in the debug spec table "Suggested Trigger Timings", to
avoid the footgun of replaying a load (which may have side effects) when
the breakpoint trap handler returns.

reference: https://github.com/riscv-software-src/riscv-isa-sim/pull/1208#issuecomment-1373035906

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The legalize_timing() depends on select, execution, load, and store,
which are updated in the same function tdata1_write(). As a result,
reordering statements in the tdata1_write() may break the functionality.

Passing those variables as parameters to legalize_timing() does not
solve the problem. Thus, we give the original write value and the masks
of the variables to the legalize_timing(). This makes the legalization
function independent of the updating variables and resolves the issue.

reference: https://github.com/riscv-software-src/riscv-isa-sim/pull/1214

Run Spike and HTIF in a single thread, rather than two

For NS16550 UART, poll stdin less often

The two-thread approach was originally motivated by making Spike look
as similar as possible to other HTIF targets.  But we can get the same
semantics without threading by running the simulator inside of the HTIF
host's idle loop instead of performing a context switch.

This was motivated by speeding up the simulator on Mac OS (it's worth
around 20% because using pthread condition variables to force strict
alternation is very slow).  But I think it also simplifies the control
flow enough to justify it on that basis, too.

Automatically test that external debug still works.

On my Mac Mini, calling `poll()` on stdin takes around 10 us, and we
are invoking it every 20 us or so.  Reduce the frequency of polling
by 16x when not actively receiving data, thereby reducing the fraction
of time spent in `poll()` to a trivial amount.

Fix supported debug version, use extension names

Addresses #1221

this is to properly handle potential 64-bit overflow in (base + size)
expression

The method can simplify proper processing of sitiations when
(base + size) overflows 64-bit interger.

NFT. We also mark `base` and `size` fields as private.

NFC. The intention is for `base` and `size` fields of mem_cfg_t
to be private members. This is the fist part of this commit.

Only update histogram when histogramming

It dates back to when this code was ifdef'd.

This is worth a 1.4x speedup on the slow path (when not histogramming).

Control mmu-dirtying via command line