sys: support type aliases (aka typedefs)

Complex types that are often repeated can be given short type aliases using the
following syntax:

```
type identifier underlying_type
```

For example:

```
type signalno int32[0:65]
type net_port proc[20000, 4, int16be]
```

Then, type alias can be used instead of the underlying type in any contexts.
Underlying type needs to be described as if it's a struct field, that is,
with the base type if it's required. However, type alias can be used as syscall
arguments as well. Underlying types are currently restricted to integer types,
`ptr`, `ptr64`, `const`, `flags` and `proc` types.

1 files changed, 5 insertions, 0 deletions

diff --git a/pkg/compiler/compiler.go b/pkg/compiler/compiler.go
index d250eda68..0be7f2817 100644
--- a/pkg/compiler/compiler.go
+++ b/pkg/compiler/compiler.go
@@ -53,6 +53,7 @@ func Compile(desc *ast.Description, consts map[string]uint64, target *targets.Ta
 		ptrSize:      target.PtrSize,
 		unsupported:  make(map[string]bool),
 		resources:    make(map[string]*ast.Resource),
+		typedefs:     make(map[string]*ast.TypeDef),
 		structs:      make(map[string]*ast.Struct),
 		intFlags:     make(map[string]*ast.IntFlags),
 		strFlags:     make(map[string]*ast.StrFlags),
@@ -89,6 +90,7 @@ type compiler struct {
 
 	unsupported map[string]bool
 	resources   map[string]*ast.Resource
+	typedefs    map[string]*ast.TypeDef
 	structs     map[string]*ast.Struct
 	intFlags    map[string]*ast.IntFlags
 	strFlags    map[string]*ast.StrFlags
@@ -163,6 +165,9 @@ func (comp *compiler) getTypeDesc(t *ast.Type) *typeDesc {
 	if comp.structs[t.Ident] != nil {
 		return typeStruct
 	}
+	if comp.typedefs[t.Ident] != nil {
+		return typeTypedef
+	}
 	return nil
 }