prog: support optional resources

docs/syscall_descriptions_syntax.md

@@ -263,6 +263,31 @@ Each resource type must be "produced" (used as an output) by at least one syscal
 (outside of unions and optional pointers) and "consumed" (used as an input)
 by at least one syscall.
 
+This restriction helps automatically determine the dependent syscalls there's no reason
+to fuzz. But in some cases one might not need such a strict validation. For example,
+consider the following minimalistic syzlang description:
+
+```
+resource inout_resource[int32]: 0
+
+test$use_resource(a ptr[inout, inout_resource_struct])
+
+inout_resource_struct {
+  field inout_resource
+}
+```
+
+Syzkaller would conclude that there's no way to construct `inout_resource` (which is
+necessary to generate `inout_resource_struct`) and disable the `test$use_resource` call.
+However, the resource is obviously not mandatory here.
+
+To indicate this to syzkaller, you may mark the resource as optional:
+
+```
+resource inout_resource[int32, opt]
+```
+
+
 ## Type Aliases
 
 Complex types that are often repeated can be given short type aliases using the

pkg/ast/ast.go

@@ -98,6 +98,7 @@ type Resource struct {
 	Name   *Ident
 	Base   *Type
 	Values []*Int
+	Args   []*Type
 }
 
 func (n *Resource) Info() (Pos, string, string) {

pkg/ast/clone.go

@@ -59,6 +59,7 @@ func (n *Resource) Clone() Node {
 		Name:   n.Name.Clone().(*Ident),
 		Base:   n.Base.Clone().(*Type),
 		Values: cloneInts(n.Values),
+		Args:   cloneTypes(n.Args),
 	}
 }
 

pkg/ast/format.go

@@ -95,7 +95,12 @@ func (n *Define) serialize(w io.Writer) {
 }
 
 func (n *Resource) serialize(w io.Writer) {
-	fmt.Fprintf(w, "resource %v[%v]", n.Name.Name, fmtType(n.Base))
+	fmt.Fprintf(w, "resource %v[%v", n.Name.Name, fmtType(n.Base))
+	for _, a := range n.Args {
+		fmt.Fprintf(w, ", ")
+		a.serialize(w)
+	}
+	fmt.Fprintf(w, "]")
 	for i, v := range n.Values {
 		fmt.Fprintf(w, "%v%v", comma(i, ": "), fmtInt(v))
 	}

pkg/ast/parser.go

@@ -242,6 +242,10 @@ func (p *parser) parseResource() *Resource {
 	name := p.parseIdent()
 	p.consume(tokLBrack)
 	base := p.parseType()
+	var args []*Type
+	if p.tryConsume(tokComma) {
+		args = append(args, p.parseType())
+	}
 	p.consume(tokRBrack)
 	var values []*Int
 	if p.tryConsume(tokColon) {
@@ -254,6 +258,7 @@ func (p *parser) parseResource() *Resource {
 		Pos:    pos0,
 		Name:   name,
 		Base:   base,
+		Args:   args,
 		Values: values,
 	}
 }

pkg/ast/testdata/all.txt

@@ -30,3 +30,5 @@ condFields {
 	f3	int16	(out, if[val[mask] & SOME_CONST & OTHER_CONST == val[mask] & CONST_X])
 	f4	int16	(out, if[val[flags] & SOME_CONST])
 }
+
+resource some_resource[int32, opt]

pkg/ast/walk.go

@@ -59,6 +59,9 @@ func (n *Resource) walk(cb func(Node)) {
 	for _, v := range n.Values {
 		cb(v)
 	}
+	for _, a := range n.Args {
+		cb(a)
+	}
 }
 
 func (n *TypeDef) walk(cb func(Node)) {

pkg/compiler/check.go

@@ -304,6 +304,7 @@ func (comp *compiler) checkTypes() {
 		switch n := decl.(type) {
 		case *ast.Resource:
 			comp.checkType(checkCtx{}, n.Base, checkIsResourceBase)
+			comp.checkResource(n)
 		case *ast.Struct:
 			comp.checkStruct(checkCtx{}, n)
 		case *ast.Call:
@@ -312,6 +313,13 @@ func (comp *compiler) checkTypes() {
 	}
 }
 
+func (comp *compiler) checkResource(n *ast.Resource) {
+	args, _ := removeOpt(n.Args)
+	if len(args) > 0 {
+		comp.error(n.Pos, "unexpected resource arguments, only opt is supported now")
+	}
+}
+
 func (comp *compiler) checkTypeValues() {
 	for _, decl := range comp.desc.Nodes {
 		switch n := decl.(type) {
@@ -1104,7 +1112,7 @@ func (comp *compiler) checkTypeBasic(t *ast.Type, desc *typeDesc, flags checkFla
 }
 
 func (comp *compiler) checkTypeArgs(t *ast.Type, desc *typeDesc, flags checkFlags) []*ast.Type {
-	args, opt := removeOpt(t)
+	args, opt := removeOpt(t.Args)
 	if opt != nil {
 		if len(opt.Args) != 0 {
 			comp.error(opt.Pos, "opt can't have arguments")

pkg/compiler/compiler.go

@@ -306,7 +306,7 @@ func (comp *compiler) getArgsBase(t *ast.Type, isArg bool) (*typeDesc, []*ast.Ty
 	if desc == nil {
 		panic(fmt.Sprintf("no type desc for %#v", *t))
 	}
-	args, opt := removeOpt(t)
+	args, opt := removeOpt(t.Args)
 	com := genCommon(t.Ident, sizeUnassigned, opt != nil)
 	base := genIntCommon(com, 0, false)
 	if desc.NeedBase {
@@ -366,8 +366,7 @@ func (comp *compiler) foreachSubType(t *ast.Type, isArg bool,
 	}
 }
 
-func removeOpt(t *ast.Type) ([]*ast.Type, *ast.Type) {
-	args := t.Args
+func removeOpt(args []*ast.Type) ([]*ast.Type, *ast.Type) {
 	if last := len(args) - 1; last >= 0 && args[last].Ident == "opt" {
 		return args[:last], args[last]
 	}

pkg/compiler/gen.go

@@ -34,6 +34,9 @@ func (comp *compiler) genResource(n *ast.Resource) *prog.ResourceDesc {
 	res := &prog.ResourceDesc{
 		Name: n.Name.Name,
 	}
+	if _, opt := removeOpt(n.Args); opt != nil {
+		res.Optional = true
+	}
 	for n != nil {
 		res.Values = append(genIntArray(n.Values), res.Values...)
 		res.Kind = append([]string{n.Name.Name}, res.Kind...)

pkg/compiler/testdata/all.txt

@@ -369,3 +369,11 @@ union$conditional3 [
 ]
 
 conditional(a ptr[in, struct$conditional])
+
+resource opt_resource[int32, opt]
+
+test$use_optional_resource(a ptr[inout, opt_resource_struct])
+
+opt_resource_struct {
+	f	opt_resource
+}

pkg/compiler/testdata/errors.txt

@@ -507,3 +507,5 @@ conditional_fields_union2 [
 	u2	int32 ### either no fields have conditions or all except the last
 	u3	int32
 ]
+
+resource opt_resource[int32, custom_arg] ### unexpected resource arguments, only opt is supported now

prog/resources.go

@@ -151,7 +151,7 @@ func (target *Target) getInputResources(c *Syscall) []*ResourceDesc {
 		}
 		switch typ1 := typ.(type) {
 		case *ResourceType:
-			if !ctx.Optional && !dedup[typ1.Desc] {
+			if !ctx.Optional && !dedup[typ1.Desc] && !typ1.Desc.Optional {
 				dedup[typ1.Desc] = true
 				resources = append(resources, typ1.Desc)
 			}

prog/types.go

@@ -310,10 +310,11 @@ type FlagDesc struct {
 }
 
 type ResourceDesc struct {
-	Name   string
-	Kind   []string
-	Values []uint64
-	Ctors  []ResourceCtor
+	Name     string
+	Optional bool
+	Kind     []string
+	Values   []uint64
+	Ctors    []ResourceCtor
 }
 
 type ResourceCtor struct {

sys/test/test.txt

@@ -774,6 +774,14 @@ syz_use_missing {
 	a1	syz_missing_const_struct
 }
 
+resource inout_resource[fd, opt]
+
+test$use_resource(a ptr[inout, inout_resource_struct])
+
+inout_resource_struct {
+	field	inout_resource
+}
+
 # Hints tests.
 
 test$hint_int(a0 ptr[in, hint_ints])