decide which.

The obvious thing for cgo to do is to process the preamble, expanding
#includes and processing the corresponding C code. That would require
a full C parser and type checker that was also aware of any extensions
known to the system compiler (for example, all the GNU C extensions) as
well as the system-specific header locations and system-specific
pre-#defined macros. This is certainly possible to do, but it is an
enormous amount of work.

		}
	case fm&fs.ModeNamedPipe != 0:
		h.Typeflag = TypeFifo
	case fm&fs.ModeSocket != 0:
		return nil, fmt.Errorf("archive/tar: sockets not supported")
	default:
		return nil, fmt.Errorf("archive/tar: unknown file mode %v", fm)
	}
	if fm&fs.ModeSetuid != 0 {
		h.Mode |= c_ISUID
	}
	if fm&fs.ModeSetgid != 0 {
		h.Mode |= c_ISGID
	}
	if fm&fs.ModeSticky != 0 {
		h.Mode |= c_ISVTX
	}

					}
				case testClose:
					err := tw.Close()
					if !equalError(err, tf.wantErr) {
						t.Fatalf("test %d, Close() = %v, want %v", i, err, tf.wantErr)
					}
				default:
					t.Fatalf("test %d, unknown test operation: %T", i, tf)
				}
			}

			if v.file != "" {
				want, err := os.ReadFile(v.file)
				if err != nil {
					t.Fatalf("ReadFile() = %v, want nil", err)
				}
				got := buf.Bytes()

			}
			buf.WriteByte(']')
		}

	case *types.TypeParam:
		// Type parameter names may change, so use a placeholder instead.
		fmt.Fprintf(buf, "$%d", typ.Index())

	default:
		panic(fmt.Sprintf("unknown type %T", typ))
	}
}

func (w *Walker) writeSignature(buf *bytes.Buffer, sig *types.Signature) {
	if tparams := sig.TypeParams(); tparams != nil {
		w.writeTypeParams(buf, tparams, true)
	}

---
title: "Go, Backwards Compatibility, and GODEBUG"
layout: article
---

<!--
This document is kept in the Go repo, not x/website,
because it documents the full list of known GODEBUG settings,
which are tied to a specific release.
-->

## Introduction {#intro}

Go's emphasis on backwards compatibility is one of its key strengths.
There are, however, times when we cannot maintain complete compatibility.

	switch {
	case major == "0" && (minor == "0" || minor == "1"):
		is1x0 = false
	case major == "1" && minor == "0":
		is1x0 = true
	case major != "" || minor != "":
		return nil, nil // Unknown GNU sparse PAX version
	case hdr.PAXRecords[paxGNUSparseMap] != "":
		is1x0 = false // 0.0 and 0.1 did not have explicit version records, so guess
	default:
		return nil, nil // Not a PAX format GNU sparse file.
	}

		if !strings.HasSuffix(s, "\n") {
			s += "\n"
		}
		errBuf.WriteString(s)
	}
	for _, flag := range flags {
		switch flag {
		case "dynlink":
			ctxt.Flag_dynlink = true
		default:
			t.Errorf("unknown flag %s", flag)
		}
	}
	pList.Firstpc, ok = parser.Parse()
	obj.Flushplist(ctxt, pList, nil)
	if ok && !failed {
		t.Errorf("asm: %s had no errors", file)
	}

	errors := map[string]string{}

		p.next()
		scale = p.parseScale(p.next().String())
	}
	return r1, r2, scale, true
}

// registerShift parses an ARM/ARM64 shifted register reference and returns the encoded representation.
// There is known to be a register (current token) and a shift operator (peeked token).
func (p *Parser) registerShift(name string, prefix rune) int64 {
	if prefix != 0 {
		p.errorf("prefix %c not allowed for shifted register: $%s", prefix, name)