all: determine patched symbols for focused fuzzing

Hash the code section of the individual symbols from vmlinux.o and use
it to determine the functions that changed their bodies between the base
and the patched build.

If the number of affected symbols is reasonable (<5%), fuzz it with the
highest priority.

1 files changed, 52 insertions, 0 deletions

diff --git a/pkg/build/linux.go b/pkg/build/linux.go
index bb5de4f28..e19eec60e 100644
--- a/pkg/build/linux.go
+++ b/pkg/build/linux.go
@@ -10,6 +10,7 @@ import (
 	"debug/elf"
 	"encoding/hex"
 	"fmt"
+	"io"
 	"os"
 	"path"
 	"path/filepath"
@@ -257,6 +258,57 @@ func queryLinuxCompiler(kernelDir string) (string, error) {
 	return string(result[1]), nil
 }
 
+// ElfSymbolHashes returns a map of sha256 hashes per a symbol contained in the elf file.
+// It's best to call it on vmlinux.o since PCs in the binary code are not patched yet.
+func ElfSymbolHashes(bin string) (map[string]string, error) {
+	file, err := elf.Open(bin)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+
+	symbols, err := file.Symbols()
+	if err != nil {
+		return nil, err
+	}
+
+	textSection := file.Section(".text")
+	if textSection == nil {
+		return nil, fmt.Errorf(".text section not found")
+	}
+
+	sectionReader, ok := textSection.Open().(io.ReaderAt)
+	if !ok {
+		return nil, fmt.Errorf(".text section reader does not support ReadAt")
+	}
+
+	hashes := make(map[string]string)
+	for _, s := range symbols {
+		if elf.ST_TYPE(s.Info) != elf.STT_FUNC || s.Size == 0 {
+			continue
+		}
+
+		if s.Section >= elf.SHN_LORESERVE || int(s.Section) >= len(file.Sections) ||
+			file.Sections[s.Section] != textSection {
+			continue
+		}
+
+		offset := s.Value - textSection.Addr
+		if offset+s.Size > textSection.Size {
+			continue
+		}
+
+		code := make([]byte, s.Size)
+		_, err := sectionReader.ReadAt(code, int64(offset))
+		if err != nil {
+			continue
+		}
+		hash := sha256.Sum256(code)
+		hashes[s.Name] = hex.EncodeToString(hash[:])
+	}
+	return hashes, nil
+}
+
 // elfBinarySignature calculates signature of an elf binary aiming at runtime behavior
 // (text/data, debug info is ignored).
 func elfBinarySignature(bin string, tracer debugtracer.DebugTracer) (string, error) {