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|
package ebpf
import (
"fmt"
"github.com/cilium/ebpf/asm"
"github.com/cilium/ebpf/internal/btf"
)
// link resolves bpf-to-bpf calls.
//
// Each library may contain multiple functions / labels, and is only linked
// if prog references one of these functions.
//
// Libraries also linked.
func link(prog *ProgramSpec, libs []*ProgramSpec) error {
var (
linked = make(map[*ProgramSpec]bool)
pending = []asm.Instructions{prog.Instructions}
insns asm.Instructions
)
for len(pending) > 0 {
insns, pending = pending[0], pending[1:]
for _, lib := range libs {
if linked[lib] {
continue
}
needed, err := needSection(insns, lib.Instructions)
if err != nil {
return fmt.Errorf("linking %s: %w", lib.Name, err)
}
if !needed {
continue
}
linked[lib] = true
prog.Instructions = append(prog.Instructions, lib.Instructions...)
pending = append(pending, lib.Instructions)
if prog.BTF != nil && lib.BTF != nil {
if err := btf.ProgramAppend(prog.BTF, lib.BTF); err != nil {
return fmt.Errorf("linking BTF of %s: %w", lib.Name, err)
}
}
}
}
return nil
}
func needSection(insns, section asm.Instructions) (bool, error) {
// A map of symbols to the libraries which contain them.
symbols, err := section.SymbolOffsets()
if err != nil {
return false, err
}
for _, ins := range insns {
if ins.Reference == "" {
continue
}
if ins.OpCode.JumpOp() != asm.Call || ins.Src != asm.PseudoCall {
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, so we have to link it.
return true, nil
}
// None of the functions in the section are called.
return false, nil
}
func fixupJumpsAndCalls(insns asm.Instructions) error {
symbolOffsets := make(map[string]asm.RawInstructionOffset)
iter := insns.Iterate()
for iter.Next() {
ins := iter.Ins
if ins.Symbol == "" {
continue
}
if _, ok := symbolOffsets[ins.Symbol]; ok {
return fmt.Errorf("duplicate symbol %s", ins.Symbol)
}
symbolOffsets[ins.Symbol] = iter.Offset
}
iter = insns.Iterate()
for iter.Next() {
i := iter.Index
offset := iter.Offset
ins := iter.Ins
switch {
case ins.IsFunctionCall() && ins.Constant == -1:
// Rewrite bpf to bpf call
callOffset, ok := symbolOffsets[ins.Reference]
if !ok {
return fmt.Errorf("instruction %d: reference to missing symbol %s", i, ins.Reference)
}
ins.Constant = int64(callOffset - offset - 1)
case ins.OpCode.Class() == asm.JumpClass && ins.Offset == -1:
// Rewrite jump to label
jumpOffset, ok := symbolOffsets[ins.Reference]
if !ok {
return fmt.Errorf("instruction %d: reference to missing symbol %s", i, ins.Reference)
}
ins.Offset = int16(jumpOffset - offset - 1)
}
}
return nil
}
|
