// Copyright 2018 syzkaller project authors. All rights reserved.
// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.

package host

import (
	"github.com/google/syzkaller/pkg/log"
	"github.com/google/syzkaller/prog"
)

// DetectSupportedSyscalls returns list on supported and unsupported syscalls on the host.
// For unsupported syscalls it also returns reason as to why it is unsupported.
func DetectSupportedSyscalls(target *prog.Target, sandbox string, enabled map[*prog.Syscall]bool) (
	map[*prog.Syscall]bool, map[*prog.Syscall]string, error) {
	log.Logf(1, "detecting supported syscalls")
	supported := make(map[*prog.Syscall]bool)
	unsupported := make(map[*prog.Syscall]string)
	const disabledAttribute = "has disabled attribute in descriptions"
	// These do not have own host and parasitize on some other OS.
	if noHostChecks(target) {
		for _, c := range target.Syscalls {
			if c.Attrs.Disabled {
				unsupported[c] = disabledAttribute
			} else {
				supported[c] = true
			}
		}
	} else {
		for _, c := range target.Syscalls {
			ok, reason := false, ""
			switch {
			case c.Attrs.Disabled:
				ok = false
				reason = disabledAttribute
			case !enabled[c]:
				ok = false
				reason = "not in set of enabled calls"
			case c.CallName == "syz_execute_func":
				// syz_execute_func caused multiple problems:
				// 1. First it lead to corpus explosion. The program used existing values in registers
				// to pollute output area. We tried to zero registers (though, not reliably).
				// 2. It lead to explosion again. The exact mechanics are unknown, here is one sample:
				// syz_execute_func(&(0x7f0000000440)="f2af91930f0124eda133fa20430fbafce842f66188d0d4
				//	430fc7f314c1ab5bf9e2f9660f3a0fae5e090000ba023c1fb63ac4817d73d74ec482310d46f44
				//	9f216c863fa438036a91bdbae95aaaa420f383c02c401405c6bfd49d768d768f833fefbab6464
				//	660f38323c8f26dbc1a1fe5ff6f6df0804f4c4efa59c0f01c4288ba6452e000054c4431d5cc100")
				// 3. The code can also execute syscalls (and it is know to), but it's not subject to
				// target.SanitizeCall. As the result it can do things that programs are not supposed to do.
				// 4. Besides linux, corpus explosion also happens on freebsd and is clearly attributable
				// to syz_execute_func based on corpus contents. Mechanics are also not known.
				// It also did not cause finding of any new bugs (at least not that I know of).
				// Let's disable it for now until we figure out how to resolve all these problems.
				ok = false
				reason = "always disabled for now"
			default:
				ok, reason = isSupported(c, target, sandbox)
			}
			if ok {
				supported[c] = true
			} else {
				if reason == "" {
					reason = "unknown"
				}
				unsupported[c] = reason
			}
		}
	}
	return supported, unsupported, nil
}

var testFallback = false
