mirror of
https://github.com/moby/moby.git
synced 2022-11-09 12:21:53 -05:00
288 lines
8 KiB
Go
288 lines
8 KiB
Go
package link
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import (
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"debug/elf"
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"errors"
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"fmt"
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"os"
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"path/filepath"
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"regexp"
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"sync"
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"github.com/cilium/ebpf"
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"github.com/cilium/ebpf/internal"
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)
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var (
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uprobeEventsPath = filepath.Join(tracefsPath, "uprobe_events")
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// rgxUprobeSymbol is used to strip invalid characters from the uprobe symbol
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// as they are not allowed to be used as the EVENT token in tracefs.
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rgxUprobeSymbol = regexp.MustCompile("[^a-zA-Z0-9]+")
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uprobeRetprobeBit = struct {
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once sync.Once
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value uint64
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err error
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}{}
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// ErrNoSymbol indicates that the given symbol was not found
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// in the ELF symbols table.
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ErrNoSymbol = errors.New("not found")
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)
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// Executable defines an executable program on the filesystem.
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type Executable struct {
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// Path of the executable on the filesystem.
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path string
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// Parsed ELF symbols and dynamic symbols offsets.
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offsets map[string]uint64
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}
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// UprobeOptions defines additional parameters that will be used
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// when loading Uprobes.
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type UprobeOptions struct {
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// Symbol offset. Must be provided in case of external symbols (shared libs).
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// If set, overrides the offset eventually parsed from the executable.
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Offset uint64
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// Only set the uprobe on the given process ID. Useful when tracing
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// shared library calls or programs that have many running instances.
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PID int
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}
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// To open a new Executable, use:
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//
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// OpenExecutable("/bin/bash")
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//
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// The returned value can then be used to open Uprobe(s).
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func OpenExecutable(path string) (*Executable, error) {
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if path == "" {
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return nil, fmt.Errorf("path cannot be empty")
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}
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f, err := os.Open(path)
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if err != nil {
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return nil, fmt.Errorf("open file '%s': %w", path, err)
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}
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defer f.Close()
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se, err := internal.NewSafeELFFile(f)
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if err != nil {
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return nil, fmt.Errorf("parse ELF file: %w", err)
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}
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if se.Type != elf.ET_EXEC && se.Type != elf.ET_DYN {
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// ELF is not an executable or a shared object.
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return nil, errors.New("the given file is not an executable or a shared object")
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}
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ex := Executable{
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path: path,
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offsets: make(map[string]uint64),
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}
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if err := ex.load(se); err != nil {
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return nil, err
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}
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return &ex, nil
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}
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func (ex *Executable) load(f *internal.SafeELFFile) error {
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syms, err := f.Symbols()
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if err != nil && !errors.Is(err, elf.ErrNoSymbols) {
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return err
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}
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dynsyms, err := f.DynamicSymbols()
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if err != nil && !errors.Is(err, elf.ErrNoSymbols) {
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return err
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}
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syms = append(syms, dynsyms...)
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for _, s := range syms {
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if elf.ST_TYPE(s.Info) != elf.STT_FUNC {
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// Symbol not associated with a function or other executable code.
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continue
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}
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off := s.Value
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// Loop over ELF segments.
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for _, prog := range f.Progs {
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// Skip uninteresting segments.
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if prog.Type != elf.PT_LOAD || (prog.Flags&elf.PF_X) == 0 {
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continue
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}
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if prog.Vaddr <= s.Value && s.Value < (prog.Vaddr+prog.Memsz) {
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// If the symbol value is contained in the segment, calculate
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// the symbol offset.
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//
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// fn symbol offset = fn symbol VA - .text VA + .text offset
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//
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// stackoverflow.com/a/40249502
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off = s.Value - prog.Vaddr + prog.Off
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break
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}
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}
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ex.offsets[s.Name] = off
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}
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return nil
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}
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func (ex *Executable) offset(symbol string) (uint64, error) {
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if off, ok := ex.offsets[symbol]; ok {
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// Symbols with location 0 from section undef are shared library calls and
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// are relocated before the binary is executed. Dynamic linking is not
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// implemented by the library, so mark this as unsupported for now.
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//
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// Since only offset values are stored and not elf.Symbol, if the value is 0,
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// assume it's an external symbol.
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if off == 0 {
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return 0, fmt.Errorf("cannot resolve %s library call '%s', "+
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"consider providing the offset via options: %w", ex.path, symbol, ErrNotSupported)
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}
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return off, nil
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}
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return 0, fmt.Errorf("symbol %s: %w", symbol, ErrNoSymbol)
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}
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// Uprobe attaches the given eBPF program to a perf event that fires when the
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// given symbol starts executing in the given Executable.
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// For example, /bin/bash::main():
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//
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// ex, _ = OpenExecutable("/bin/bash")
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// ex.Uprobe("main", prog, nil)
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//
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// When using symbols which belongs to shared libraries,
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// an offset must be provided via options:
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//
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// up, err := ex.Uprobe("main", prog, &UprobeOptions{Offset: 0x123})
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//
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// Losing the reference to the resulting Link (up) will close the Uprobe
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// and prevent further execution of prog. The Link must be Closed during
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// program shutdown to avoid leaking system resources.
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//
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// Functions provided by shared libraries can currently not be traced and
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// will result in an ErrNotSupported.
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func (ex *Executable) Uprobe(symbol string, prog *ebpf.Program, opts *UprobeOptions) (Link, error) {
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u, err := ex.uprobe(symbol, prog, opts, false)
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if err != nil {
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return nil, err
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}
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err = u.attach(prog)
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if err != nil {
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u.Close()
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return nil, err
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}
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return u, nil
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}
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// Uretprobe attaches the given eBPF program to a perf event that fires right
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// before the given symbol exits. For example, /bin/bash::main():
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//
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// ex, _ = OpenExecutable("/bin/bash")
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// ex.Uretprobe("main", prog, nil)
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//
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// When using symbols which belongs to shared libraries,
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// an offset must be provided via options:
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//
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// up, err := ex.Uretprobe("main", prog, &UprobeOptions{Offset: 0x123})
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//
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// Losing the reference to the resulting Link (up) will close the Uprobe
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// and prevent further execution of prog. The Link must be Closed during
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// program shutdown to avoid leaking system resources.
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//
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// Functions provided by shared libraries can currently not be traced and
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// will result in an ErrNotSupported.
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func (ex *Executable) Uretprobe(symbol string, prog *ebpf.Program, opts *UprobeOptions) (Link, error) {
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u, err := ex.uprobe(symbol, prog, opts, true)
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if err != nil {
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return nil, err
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}
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err = u.attach(prog)
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if err != nil {
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u.Close()
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return nil, err
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}
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return u, nil
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}
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// uprobe opens a perf event for the given binary/symbol and attaches prog to it.
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// If ret is true, create a uretprobe.
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func (ex *Executable) uprobe(symbol string, prog *ebpf.Program, opts *UprobeOptions, ret bool) (*perfEvent, error) {
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if prog == nil {
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return nil, fmt.Errorf("prog cannot be nil: %w", errInvalidInput)
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}
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if prog.Type() != ebpf.Kprobe {
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return nil, fmt.Errorf("eBPF program type %s is not Kprobe: %w", prog.Type(), errInvalidInput)
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}
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var offset uint64
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if opts != nil && opts.Offset != 0 {
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offset = opts.Offset
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} else {
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off, err := ex.offset(symbol)
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if err != nil {
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return nil, err
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}
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offset = off
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}
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pid := perfAllThreads
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if opts != nil && opts.PID != 0 {
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pid = opts.PID
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}
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// Use uprobe PMU if the kernel has it available.
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tp, err := pmuUprobe(symbol, ex.path, offset, pid, ret)
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if err == nil {
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return tp, nil
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}
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if err != nil && !errors.Is(err, ErrNotSupported) {
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return nil, fmt.Errorf("creating perf_uprobe PMU: %w", err)
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}
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// Use tracefs if uprobe PMU is missing.
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tp, err = tracefsUprobe(uprobeSanitizedSymbol(symbol), ex.path, offset, pid, ret)
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if err != nil {
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return nil, fmt.Errorf("creating trace event '%s:%s' in tracefs: %w", ex.path, symbol, err)
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}
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return tp, nil
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}
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// pmuUprobe opens a perf event based on the uprobe PMU.
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func pmuUprobe(symbol, path string, offset uint64, pid int, ret bool) (*perfEvent, error) {
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return pmuProbe(uprobeType, symbol, path, offset, pid, ret)
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}
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// tracefsUprobe creates a Uprobe tracefs entry.
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func tracefsUprobe(symbol, path string, offset uint64, pid int, ret bool) (*perfEvent, error) {
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return tracefsProbe(uprobeType, symbol, path, offset, pid, ret)
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}
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// uprobeSanitizedSymbol replaces every invalid characted for the tracefs api with an underscore.
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func uprobeSanitizedSymbol(symbol string) string {
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return rgxUprobeSymbol.ReplaceAllString(symbol, "_")
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}
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// uprobePathOffset creates the PATH:OFFSET token for the tracefs api.
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func uprobePathOffset(path string, offset uint64) string {
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return fmt.Sprintf("%s:%#x", path, offset)
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}
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func uretprobeBit() (uint64, error) {
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uprobeRetprobeBit.once.Do(func() {
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uprobeRetprobeBit.value, uprobeRetprobeBit.err = determineRetprobeBit(uprobeType)
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})
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return uprobeRetprobeBit.value, uprobeRetprobeBit.err
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}
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