Separated compiler into its own package

src/build/compiler/Result.go

@@ -0,0 +1,106 @@
+package compiler
+
+import (
+	"bufio"
+	"os"
+
+	"git.akyoto.dev/cli/q/src/build/arch/x64"
+	"git.akyoto.dev/cli/q/src/build/asm"
+	"git.akyoto.dev/cli/q/src/build/core"
+	"git.akyoto.dev/cli/q/src/build/elf"
+	"git.akyoto.dev/cli/q/src/build/os/linux"
+)
+
+// Result contains all the compiled functions in a build.
+type Result struct {
+	Main             *core.Function
+	Functions        map[string]*core.Function
+	InstructionCount int
+	DataCount        int
+}
+
+// finalize generates the final machine code.
+func (r *Result) finalize() ([]byte, []byte) {
+	// This will be the entry point of the executable.
+	// The only job of the entry function is to call `main` and exit cleanly.
+	// The reason we call `main` instead of using `main` itself is to place
+	// a return address on the stack, which allows return statements in `main`.
+	final := asm.Assembler{
+		Instructions: make([]asm.Instruction, 0, r.InstructionCount+4),
+		Data:         make(map[string][]byte, r.DataCount),
+	}
+
+	final.Call("main")
+	final.RegisterNumber(asm.MOVE, x64.SyscallRegisters[0], linux.Exit)
+	final.RegisterNumber(asm.MOVE, x64.SyscallRegisters[1], 0)
+	final.Syscall()
+
+	// This will place the main function immediately after the entry point
+	// and also add everything the main function calls recursively.
+	r.eachFunction(r.Main, map[*core.Function]bool{}, func(f *core.Function) {
+		final.Merge(f.Assembler)
+	})
+
+	code, data := final.Finalize()
+	return code, data
+}
+
+// eachFunction recursively finds all the calls to external functions.
+// It avoids calling the same function twice with the help of a hashmap.
+func (r *Result) eachFunction(caller *core.Function, traversed map[*core.Function]bool, call func(*core.Function)) {
+	call(caller)
+	traversed[caller] = true
+
+	for _, x := range caller.Assembler.Instructions {
+		if x.Mnemonic != asm.CALL {
+			continue
+		}
+
+		name := x.Data.(*asm.Label).Name
+		callee, exists := r.Functions[name]
+
+		if !exists {
+			continue
+		}
+
+		if traversed[callee] {
+			continue
+		}
+
+		r.eachFunction(callee, traversed, call)
+	}
+}
+
+// PrintInstructions prints out the generated instructions.
+func (r *Result) PrintInstructions() {
+	r.eachFunction(r.Main, map[*core.Function]bool{}, func(f *core.Function) {
+		f.PrintInstructions()
+	})
+}
+
+// Write writes an executable file to disk.
+func (r *Result) Write(path string) error {
+	code, data := r.finalize()
+	return write(path, code, data)
+}
+
+// write writes an executable file to disk.
+func write(path string, code []byte, data []byte) error {
+	file, err := os.Create(path)
+
+	if err != nil {
+		return err
+	}
+
+	buffer := bufio.NewWriter(file)
+	executable := elf.New(code, data)
+	executable.Write(buffer)
+	buffer.Flush()
+	err = file.Close()
+
+	if err != nil {
+		return err
+	}
+
+	return os.Chmod(path, 0755)
+}