gasm-sdk/debug/target_linux.go

// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: BSD-3-Clause

//go:build linux

package debug

import (
	"encoding/hex"
	"fmt"
	"os"
	"strconv"
	"strings"
	"syscall"
	"unsafe"
)

// mapRWX maps code into a read-write-execute region.
func mapRWX(code []byte) ([]byte, error) {
	const pageSize = 4096
	size := (len(code) + pageSize - 1) &^ (pageSize - 1)
	mem, err := syscall.Mmap(-1, 0, size,
		syscall.PROT_READ|syscall.PROT_WRITE|syscall.PROT_EXEC,
		syscall.MAP_PRIVATE|syscall.MAP_ANON)
	if err != nil {
		return nil, err
	}
	copy(mem, code)
	return mem, nil
}

// setupBuffers allocates buffers in the debuggee's memory.
func setupBuffers(spec string, args []byte, tmpDir string) ([]byte, error) {
	type bufSpec struct {
		name    string
		size    int
		pattern string
	}
	var specs []bufSpec
	for part := range strings.SplitSeq(spec, ",") {
		fields := strings.SplitN(part, ":", 3)
		if len(fields) != 3 {
			continue
		}
		size, err := strconv.Atoi(fields[1])
		if err != nil || size <= 0 {
			continue
		}
		specs = append(specs, bufSpec{name: fields[0], size: size, pattern: fields[2]})
	}

	if len(specs) == 0 {
		return args, nil
	}

	var bufAddrs []uint64
	for _, s := range specs {
		buf, err := syscall.Mmap(-1, 0, s.size,
			syscall.PROT_READ|syscall.PROT_WRITE,
			syscall.MAP_PRIVATE|syscall.MAP_ANON)
		if err != nil {
			return nil, fmt.Errorf("mmap buffer %s: %w", s.name, err)
		}
		fillBuffer(buf, s.pattern)
		bufAddrs = append(bufAddrs, uint64(uintptr(unsafe.Pointer(&buf[0]))))
	}

	addrFile, err := os.Create(tmpDir + "/bufaddrs")
	if err != nil {
		return nil, err
	}
	for _, addr := range bufAddrs {
		fmt.Fprintf(addrFile, "%d\n", addr)
	}
	addrFile.Close()

	return args, nil
}

// fillBuffer fills a buffer with the specified pattern.
func fillBuffer(buf []byte, pattern string) {
	switch pattern {
	case "zero":
	case "ones":
		for i := range buf {
			buf[i] = 0xFF
		}
	case "seq":
		for i := range buf {
			buf[i] = byte(i)
		}
	default:
		if data, err := hex.DecodeString(pattern); err == nil && len(data) > 0 {
			for i := range buf {
				buf[i] = data[i%len(data)]
			}
		}
	}
}