btf: rename maxTypeDepth to maxResolveDepth

Rename the constant and document where it originates. The previous
name is misleading since vmlinux BTF does contain types which are
nested more deeply than 32 items at the moment.

Signed-off-by: Lorenz Bauer <lmb@isovalent.com>

btf/core.go

@@ -799,7 +799,7 @@ func coreFindMember(typ composite, name string) (Member, bool, error) {
  if visited[target] {
  continue
  }
- if len(visited) >= maxTypeDepth {
+ if len(visited) >= maxResolveDepth {
  // This check is different than libbpf, which restricts the entire
  // path to BPF_CORE_SPEC_MAX_LEN items.
  return Member{}, false, fmt.Errorf("type is nested too deep")
@@ -895,7 +895,7 @@ func coreAreTypesCompatible(localType Type, targetType Type) error {
  )
 
  for ; l != nil && t != nil; l, t = localTs.Shift(), targetTs.Shift() {
- if depth >= maxTypeDepth {
+ if depth >= maxResolveDepth {
  return errors.New("types are nested too deep")
  }
 

btf/core_test.go

@@ -652,7 +652,7 @@ func TestCORECopyWithoutQualifiers(t *testing.T) {
  rng := testutils.Rand(t)
  root := &Int{Name: "abc"}
  v := Type(root)
- for i := 0; i < maxTypeDepth; i++ {
+ for i := 0; i < maxResolveDepth; i++ {
  q := qualifiers[rng.Intn(len(qualifiers))]
  v = q.fn(v)
  t.Log(q.name)

btf/format.go

@@ -118,7 +118,7 @@ func (gf *GoFormatter) writeType(typ Type, depth int) error {
 // uint32
 func (gf *GoFormatter) writeTypeLit(typ Type, depth int) error {
  depth++
- if depth > maxTypeDepth {
+ if depth > maxResolveDepth {
  return errNestedTooDeep
  }
 
@@ -265,7 +265,7 @@ func (gf *GoFormatter) writeStructField(m Member, depth int) error {
  }
 
  depth++
- if depth > maxTypeDepth {
+ if depth > maxResolveDepth {
  return errNestedTooDeep
  }
 
@@ -338,7 +338,7 @@ func (gf *GoFormatter) writePadding(bytes uint32) {
 
 func skipQualifiers(typ Type) Type {
  result := typ
- for depth := 0; depth <= maxTypeDepth; depth++ {
+ for depth := 0; depth <= maxResolveDepth; depth++ {
  switch v := (result).(type) {
  case qualifier:
  result = v.qualify()

btf/types.go

@@ -12,7 +12,9 @@ import (
  "github.com/cilium/ebpf/internal/sys"
 )
 
-const maxTypeDepth = 32
+// Mirrors MAX_RESOLVE_DEPTH in libbpf.
+// https://github.com/libbpf/libbpf/blob/e26b84dc330c9644c07428c271ab491b0f01f4e1/src/btf.c#L761
+const maxResolveDepth = 32
 
 // TypeID identifies a type in a BTF section.
 type TypeID = sys.TypeID
@@ -589,7 +591,7 @@ func Sizeof(typ Type) (int, error) {
  elem int64
  )
 
- for i := 0; i < maxTypeDepth; i++ {
+ for i := 0; i < maxResolveDepth; i++ {
  switch v := typ.(type) {
  case *Array:
  if n > 0 && int64(v.Nelems) > math.MaxInt64/n {
@@ -1096,7 +1098,7 @@ func newEssentialName(name string) essentialName {
 // UnderlyingType skips qualifiers and Typedefs.
 func UnderlyingType(typ Type) Type {
  result := typ
- for depth := 0; depth <= maxTypeDepth; depth++ {
+ for depth := 0; depth <= maxResolveDepth; depth++ {
  switch v := (result).(type) {
  case qualifier:
  result = v.qualify()
@@ -1115,7 +1117,7 @@ func UnderlyingType(typ Type) Type {
 // Returns the zero value and false if there is no T or if the type is nested
 // too deeply.
 func as[T Type](typ Type) (T, bool) {
- for depth := 0; depth <= maxTypeDepth; depth++ {
+ for depth := 0; depth <= maxResolveDepth; depth++ {
  switch v := (typ).(type) {
  case T:
  return v, true