rv-emu: an RISC-V emulator from scratch in C++

Development started in March 2023
First uploaded to Github on Dec 6 2023

Compile:
`make main` will build the emulator.
`make clean` will remove all object files in the build folder.
`make rebuild` is equivalent to `make clean; make main`

Usage:
`./main <args>`
Possible arguments:
-f <path to firmware>
-k <path to kernel>
-i <path to initrd>
-m <memory size, default 512MiB>
-c <hart count, default 1>
-d <path to device tree blob>
-s <path to signature output>
-e dump the whole memory into a file named "mem_dump" at exit
-p disable PTY setup for emulated UART terminal, and use stdio instead
-h print this help message and exit

External libraries used:
libelf

ELF formatted executables are supported. However, raw binaries created with objdump will also work.

By default, a pseudoterminal is created for the UART IO, which can be accessed with the command `screen /path/to/pty` in another terminal.
In the diagnostic messages at the start of the emulator, the path to the pty will be printed out.
Use -p to disable the pty and do the IO in the same terminal instead.

Compile-time options can be changed in constants.h


Instruction set: RV64IMACZicsr_Zifencei
Modes Supported: M,S,U
Virtual Memory: Supports Bare, Sv39, Sv48, Sv57

Load addresses:
Start address: 0x1000 (contains built-in hardcoded boot sequence)
DTB load address: 0x1100 (RO)
Firmware (OpenSBI, BBL etc): 0x8000'0000
Kernel: 0x8020'0000
initrd: 0x8820'0000

If firmware is not provided but kernel is, the kernel is loaded at 0x8000'0000 instead

Max sizes:
DTB: 32 KiB
Firmware: 2MiB
Kernel: 254MiB
initrd: 128MiB

Supported hardware devices:
RISC-V ACLINT MTIMER, MSWI
RISC-V PLIC
NS16550A UART serial terminal
(incomplete, does not work) virtio block device over memory-mapped IO

Defaults:
Memory: 512MiB
Harts: 1

Signature mode:
If the -s option is given, the emulator runs in signature mode, for compilance testing.
Under signature mode, debug info will be disabled.
Also, the instruction "sltiu zero, t1, 0xbad" (0xbad33013) will halt the emulator.
When halting, the emulator will dump the memory region denoted by begin_signature and 
end_signature symbols in the ELF file to the signature file.