From 31c4e1cf522f532fafd3d3ae6cec8ceeed8bc059 Mon Sep 17 00:00:00 2001
From: Paul Cacheux <paul.cacheux@datadoghq.com>
Date: Thu, 21 Apr 2022 19:57:43 +0200
Subject: [PATCH] btf: guess the number of raw types

---
 internal/btf/btf.go       |  2 +-
 internal/btf/btf_types.go | 13 ++++++++-----
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/internal/btf/btf.go b/internal/btf/btf.go
index aa4492019..85237540b 100644
--- 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
index d98c73ca5..948dd91e1 100644
--- 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 {