Extremis

( god, who programmed .iris to not be able to be commited? )

A text-based RPG written in RISC-V 32-bit assembly, simulated via QEMU.

"The universe decided it didn't want me doing anything better, like maybe getting a life."

Dependencies

• riscv32-elf-as — RISC-V assembler
• riscv32-elf-ld — RISC-V linker
• qemu-riscv32 — RISC-V user-mode emulator

On Arch Linux:

sudo pacman -S riscv64-elf-binutils qemu-user

Build & Run

make build   # assemble and link into main.bin
make run     # build + run via qemu-riscv32
make debug   # run with -strace to inspect syscalls

Project Structure

Extremis/
├── main.s                      # Entry point (_start), calls run_chapter_1
├── src/
│   ├── include/
│   │   └── function.s          # startF / endF stack frame macros
│   ├── engine/
│   │   ├── print.s             # print  — print a single null-terminated string (a0)
│   │   └── utils.s             # printl — print a list of strings (a0=addr table, a1=count)
│   ├── chapters/
│   │   └── chapter_1.s         # Chapter 1 logic; loads intro strings and calls printl
│   └── dialogue/
│       └── intro.s             # String data for the intro sequence
└── build/                      # Compiled .o files (mirrors src/ layout)

Architecture

The engine is pure RISC-V 32-bit assembly targeting the Linux ABI via QEMU user-mode emulation.

Stack Frame Convention

Every function uses the startF / endF macros from src/include/function.s to save and restore ra, s0, s1, s2 on the stack:

startF    # push: allocate 16 bytes, save ra/s0/s1/s2
...
endF      # pop:  restore ra/s0/s1/s2, deallocate 16 bytes
ret

Syscalls

Warning: RARS/MARS environment call numbers do not work under qemu-riscv32. This project uses Linux RISC-V ABI syscall numbers.

Syscall number goes in a7, invoke with ecall. Return value comes back in a0.

Output

Intent	RARS a7	Linux a7	a0	a1	a2	Notes
Print string	4	64	1 (stdout fd)	buf addr	length	Linux does NOT stop at null — pass byte len
Print char	11	64	1	char buf	1	store char in memory, pass its address
Print integer	1	—	integer	—	—	no Linux equivalent; convert to string first
Print hex integer	34	—	integer	—	—	no Linux equivalent; convert manually
Print unsigned int	36	—	integer	—	—	no Linux equivalent; convert manually

Input

Intent	RARS a7	Linux a7	a0	a1	a2	Notes
Read string	8	63	0 (stdin fd)	buf addr	max bytes	Linux returns raw bytes incl. newline
Read char	12	63	0	buf addr	1	returns a0 = bytes read; char is in buf
Read integer	5	—	—	—	—	no Linux equivalent; read string, parse it

Process

Intent	RARS a7	Linux a7	a0	Notes
Exit	10	93	—	RARS ignores a0; Linux reads it as exit status
Exit(code)	17	93	exit code	Linux exit_group

Memory

Intent	RARS a7	Linux a7	a0	Returns	Notes
Allocate (sbrk)	9	214	bytes (RARS) / new brk addr (Linux)	a0 = start of allocated block	Linux brk works differently — you set the new top, not a size

File I/O

Intent	RARS a7	Linux a7	a0	a1	a2	a3	Notes
Open file	13	56	dirfd (-100=CWD)	filename addr	flags	mode	Linux uses openat
Read file	14	63	fd	buf addr	max bytes	—	returns bytes read
Write file	15	64	fd	buf addr	byte count	—	returns bytes written
Close file	16	57	fd	—	—	—	returns 0 on success

Time

Intent	RARS a7	Linux a7	a0	a1	Notes
Time	30	113	clock id (1=REALTIME)	timespec* buf	RARS returns split lo/hi in a0/a1; Linux writes struct to buf
Sleep	32	115	clock id	timespec*	RARS takes milliseconds in a0; Linux uses clock_nanosleep with a struct

Adding Content

• New dialogue strings go in src/dialogue/.
• New chapters go in src/chapters/ and are .include'd into the chapter file that needs them.
• The Makefile auto-discovers all .s files under src/ (excluding src/include/).