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EGG, a generic processor emulator

Video tutorial

Documentation

Contributing, bugs, feature requests

EGG stands for "Emulador Genérico do Gabriel" ("Gabriel's Generic Emulator", in portuguese). It's a modular emulator for processor architetures, made for educational purpouses.

The egg package itself provides only an interface for interacting with machines, thus supporting different architeture backends. Currently, there are RISC-V IM 32 bits and a MIPS32 (experimental) backends implemented.

egg/assembler also provides a small library for creating assemblers, and the support for EGG's debugger.

UFPR students

Have any questions, or want some help? Mail me: [email protected]. Or find me at the campus and the laboratories!

Installation

Simply grab the static binary for your OS at the releases page. Or, if you have the Go compiler, build the project from source.

Note: the Windows binary is untested, as I don't have access to any Windows machine nowadays. The testing of the Darwin (MacOS) binary depends on my patience.

Quickstart

Running the emulator with an Assembly file will assemble it and start a machine to run it on. By default, the machine is a RISC-V IM 32 bits. Use the flag -a or -arch to change the architeture. Run egg -h to see all command line options and egg -l to see all supported architetures.

The Assembly syntax is architeture-dependent. Though, a library is provided for creating assembler, so backends may use the same overall syntax (both RISC-V and MIPS uses it).

An example follows:

; Semicolon makes a comment til the end of line.

; A label is defined with :.
label:
	; Instruction arguments starts with destination.
	addi t0, zero, 2

	; You may also put instructions after the labels.
label2:	add t0, t0, t0

	; There's no parenthesis as in RARS, store uses common immediates.
	sb t0, ra, 3

	; Hex, octal and binary immediates are supported.
	addi t1, zero, 0xff
	addi t1, zero, 0b010110
	addi t1, zero, 0o644
	addi t1, zero, 0755	; A leading 0 also defines an octal.

; A # defines a literal til the end of the line.
; Literals are inserted unchanged to the binary (as 'db' in other assemblers).
; If a % is followed by two hex digits, the hex value is inserted instead. Use
; %% to escape it.
msg:
#Hello, World!%0a

; Some directives are supported. "bitsxx" ones creates literal numbers in the
; code, with the bit length specified:
.bits8 0xca 0xfe 0xba 0xbe 0xde 0xad 0xbe 0xef
.bits16 0xcafe 0xbabe 0xdead 0xbeef
.bits32 0xcafebabe 0xdeadbeef
.bits64 0xcafebabedeadbeef
; The "space" directive adds some bytes of spacing in the code:
.space 16
; The "include" directive "copy-pastes" another file in the code:
.include other-asm.asm

Each architeture folder has test Assembly files you may use as examples.

Calls

Standard calls handled by the emulator are as follows. Refer to the architeture documentation on how to perform them:

• BREAK (Number 1): Transfer control to debugger or stop the machine.
  No arguments.
• READ (Number 2): Read input.
  • Argument 1: Buffer address.
  • Argument 2: Size of input in bytes.
• WRITE (Number 3): Write output.
  • Argument 1: Buffer address.
  • Argument 2: Size of output in bytes.

Debugger

The debugger interface is kinda similar to gdb, though much smaller. Use the -d flag to enter debugger uppon startup. There's no need of run command, as there's no process. The next or the continue commands may be used to start running the program normally. Use help to see all available commands.