134 lines
2.9 KiB
Go
134 lines
2.9 KiB
Go
package ebpf
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import (
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"fmt"
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"github.com/cilium/ebpf/asm"
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"github.com/cilium/ebpf/internal/btf"
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)
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// link resolves bpf-to-bpf calls.
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//
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// Each library may contain multiple functions / labels, and is only linked
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// if prog references one of these functions.
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//
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// Libraries also linked.
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func link(prog *ProgramSpec, libs []*ProgramSpec) error {
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var (
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linked = make(map[*ProgramSpec]bool)
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pending = []asm.Instructions{prog.Instructions}
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insns asm.Instructions
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)
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for len(pending) > 0 {
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insns, pending = pending[0], pending[1:]
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for _, lib := range libs {
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if linked[lib] {
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continue
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}
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needed, err := needSection(insns, lib.Instructions)
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if err != nil {
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return fmt.Errorf("linking %s: %w", lib.Name, err)
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}
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if !needed {
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continue
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}
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linked[lib] = true
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prog.Instructions = append(prog.Instructions, lib.Instructions...)
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pending = append(pending, lib.Instructions)
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if prog.BTF != nil && lib.BTF != nil {
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if err := btf.ProgramAppend(prog.BTF, lib.BTF); err != nil {
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return fmt.Errorf("linking BTF of %s: %w", lib.Name, err)
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}
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}
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}
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}
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return nil
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}
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func needSection(insns, section asm.Instructions) (bool, error) {
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// A map of symbols to the libraries which contain them.
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symbols, err := section.SymbolOffsets()
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if err != nil {
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return false, err
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}
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for _, ins := range insns {
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if ins.Reference == "" {
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continue
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}
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if ins.OpCode.JumpOp() != asm.Call || ins.Src != asm.PseudoCall {
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continue
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}
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if ins.Constant != -1 {
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// This is already a valid call, no need to link again.
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continue
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}
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if _, ok := symbols[ins.Reference]; !ok {
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// Symbol isn't available in this section
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continue
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}
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// At this point we know that at least one function in the
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// library is called from insns, so we have to link it.
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return true, nil
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}
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// None of the functions in the section are called.
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return false, nil
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}
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func fixupJumpsAndCalls(insns asm.Instructions) error {
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symbolOffsets := make(map[string]asm.RawInstructionOffset)
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iter := insns.Iterate()
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for iter.Next() {
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ins := iter.Ins
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if ins.Symbol == "" {
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continue
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}
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if _, ok := symbolOffsets[ins.Symbol]; ok {
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return fmt.Errorf("duplicate symbol %s", ins.Symbol)
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}
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symbolOffsets[ins.Symbol] = iter.Offset
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}
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iter = insns.Iterate()
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for iter.Next() {
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i := iter.Index
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offset := iter.Offset
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ins := iter.Ins
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switch {
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case ins.IsFunctionCall() && ins.Constant == -1:
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// Rewrite bpf to bpf call
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callOffset, ok := symbolOffsets[ins.Reference]
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if !ok {
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return fmt.Errorf("instruction %d: reference to missing symbol %q", i, ins.Reference)
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}
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ins.Constant = int64(callOffset - offset - 1)
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case ins.OpCode.Class() == asm.JumpClass && ins.Offset == -1:
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// Rewrite jump to label
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jumpOffset, ok := symbolOffsets[ins.Reference]
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if !ok {
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return fmt.Errorf("instruction %d: reference to missing symbol %q", i, ins.Reference)
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}
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ins.Offset = int16(jumpOffset - offset - 1)
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}
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}
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return nil
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}
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