btf: guess the number of raw types

cilium · Apr 23, 2022 · 31c4e1c · 31c4e1c
1 parent 2c93040
commit 31c4e1c
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Showing 2 changed files with 9 additions and 6 deletions.
diff --git a/internal/btf/btf.go b/internal/btf/btf.go
@@ -461,7 +461,7 @@ func parseBTF(btf io.ReaderAt, bo binary.ByteOrder) ([]rawType, stringTable, err
 	}
 
 	buf.Reset(io.NewSectionReader(btf, header.typeStart(), int64(header.TypeLen)))
-	rawTypes, err := readTypes(buf, bo)
+	rawTypes, err := readTypes(buf, bo, header.TypeLen)
 	if err != nil {
 		return nil, nil, fmt.Errorf("can't read types: %w", err)
 	}

diff --git a/internal/btf/btf_types.go b/internal/btf/btf_types.go
@@ -226,11 +226,14 @@ type btfParam struct {
 	Type    TypeID
 }
 
-func readTypes(r io.Reader, bo binary.ByteOrder) ([]rawType, error) {
-	var (
-		header btfType
-		types  []rawType
-	)
+func readTypes(r io.Reader, bo binary.ByteOrder, typeLen uint32) ([]rawType, error) {
+	var header btfType
+	// because of the interleaving between types and struct members it is difficult to
+	// precompute the numbers of raw types this will parse
+	// this "guess" is a good first estimation
+	sizeOfbtfType := uintptr(binary.Size(btfType{}))
+	tyMaxCount := uintptr(typeLen) / sizeOfbtfType / 2
+	types := make([]rawType, 0, tyMaxCount)
 
 	for id := TypeID(1); ; id++ {
 		if err := binary.Read(r, bo, &header); err == io.EOF {