support cgroup2

* only shim v2 runc v2 ("io.containerd.runc.v2") is supported
* only PID metrics is implemented. Others should be implemented in separate PRs.
* lots of code duplication in v1 metrics and v2 metrics. Dedupe should be separate PR.

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

vendor/github.com/cilium/ebpf/linker.go

@@ -0,0 +1,58 @@
+package ebpf
+
+import (
+	"github.com/cilium/ebpf/asm"
+)
+
+// link resolves bpf-to-bpf calls.
+//
+// Each section may contain multiple functions / labels, and is only linked
+// if the program being edited references one of these functions.
+//
+// Sections must not require linking themselves.
+func link(insns asm.Instructions, sections ...asm.Instructions) (asm.Instructions, error) {
+	for _, section := range sections {
+		var err error
+		insns, err = linkSection(insns, section)
+		if err != nil {
+			return nil, err
+		}
+	}
+	return insns, nil
+}
+
+func linkSection(insns, section asm.Instructions) (asm.Instructions, error) {
+	// A map of symbols to the libraries which contain them.
+	symbols, err := section.SymbolOffsets()
+	if err != nil {
+		return nil, err
+	}
+
+	for _, ins := range insns {
+		if ins.Reference == "" {
+			continue
+		}
+
+		if ins.OpCode.JumpOp() != asm.Call || ins.Src != asm.R1 {
+			continue
+		}
+
+		if ins.Constant != -1 {
+			// This is already a valid call, no need to link again.
+			continue
+		}
+
+		if _, ok := symbols[ins.Reference]; !ok {
+			// Symbol isn't available in this section
+			continue
+		}
+
+		// At this point we know that at least one function in the
+		// library is called from insns. Merge the two sections.
+		// The rewrite of ins.Constant happens in asm.Instruction.Marshal.
+		return append(insns, section...), nil
+	}
+
+	// None of the functions in the section are called. Do nothing.
+	return insns, nil
+}