fix: Get bpf prog entry func name from insns

It is possible to get wrong entry func name of bpf prog when there is
info of multiple bpf progs in the BTF.

Instead, get the very first symbol from bpf prog's instructions as its
entry func name.

Signed-off-by: Leon Hwang <[email protected]>

Author: Asphaltt

internal/pwru/bpf_prog.go

@@ -8,7 +8,6 @@ import (
 	"fmt"
 
 	"github.com/cilium/ebpf"
-	"github.com/cilium/ebpf/btf"
 	"golang.org/x/sys/unix"
 )
 
@@ -47,26 +46,15 @@ func getEntryFuncName(prog *ebpf.Program) (string, string, error) {
 		return "", "", fmt.Errorf("failed to get program info: %w", err)
 	}
 
-	id, ok := info.BTFID()
-	if !ok {
-		return "", "", fmt.Errorf("bpf program %s does not have BTF", info.Name)
-	}
-
-	handle, err := btf.NewHandleFromID(id)
-	if err != nil {
-		return "", "", fmt.Errorf("failed to get BTF handle: %w", err)
-	}
-	defer handle.Close()
-
-	spec, err := handle.Spec(nil)
+	insns, err := info.Instructions()
 	if err != nil {
-		return "", "", fmt.Errorf("failed to get BTF spec: %w", err)
+		return "", "", fmt.Errorf("failed to get program instructions: %w", err)
 	}
 
-	iter := spec.Iterate()
-	for iter.Next() {
-		if fn, ok := iter.Type.(*btf.Func); ok {
-			return fn.Name, info.Name, nil
+	for _, insn := range insns {
+		sym := insn.Symbol()
+		if sym != "" {
+			return sym, info.Name, nil
 		}
 	}