controlled by the cgocheck setting of the GODEBUG environment
variable. The default setting is GODEBUG=cgocheck=1, which implements
reasonably cheap dynamic checks. These checks may be disabled
entirely using GODEBUG=cgocheck=0. Complete checking of pointer
handling, at some cost in run time, is available by setting
GOEXPERIMENT=cgocheck2 at build time.

It is possible to defeat this enforcement by using the unsafe package,

pkg go/types, method (*Info) ObjectOf(*ast.Ident) Object
pkg go/types, method (*Info) TypeOf(ast.Expr) Type
pkg go/types, method (*Initializer) String() string
pkg go/types, method (*Interface) Complete() *Interface
pkg go/types, method (*Interface) Embedded(int) *Named
pkg go/types, method (*Interface) Empty() bool
pkg go/types, method (*Interface) ExplicitMethod(int) *Func

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.
If code depends on buggy (including insecure) behavior,
then fixing the bug will break that code.
New features can also have similar impacts:
enabling the HTTP/2 use by the HTTP client broke programs

// the [Scanner] returns it to the user. If the token is nil, the
// Scanner reads more data and continues scanning; if there is no more
// data--if atEOF was true--the [Scanner] returns. If the data does not
// yet hold a complete token, for instance if it has no newline while
// scanning lines, a [SplitFunc] can return (0, nil, nil) to signal the
// [Scanner] to read more data into the slice and try again with a

	extraLen := int(b.uint16())
	return int64(fileHeaderLen + filenameLen + extraLen), nil
}

// readDirectoryHeader attempts to read a directory header from r.
// It returns io.ErrUnexpectedEOF if it cannot read a complete header,
// and ErrFormat if it doesn't find a valid header signature.
func readDirectoryHeader(f *File, r io.Reader) error {
	var buf [directoryHeaderLen]byte
	if _, err := io.ReadFull(r, buf[:]); err != nil {

</p>

<h3 id="directives">Directives</h3>

<p>
The assembler uses various directives to bind text and data to symbol names.
For example, here is a simple complete function definition. The <code>TEXT</code>
directive declares the symbol <code>runtime·profileloop</code> and the instructions
that follow form the body of the function.

			}
		}
	}
	in.Error("recursive macro invocation")
	return 0
}

func (in *Input) Text() string {
	return in.text
}

// hash processes a # preprocessor directive. It reports whether it completes.
func (in *Input) hash() bool {
	// We have a '#'; it must be followed by a known word (define, include, etc.).
	tok := in.Stack.Next()
	if tok != scanner.Ident {
		in.expectText("expected identifier after '#'")
	}

	// limit (8KB), we stop growing the source string once the limit
	// is reached and keep reusing the same source string - that
	// should therefore be always resident in the L1 cache - until we
	// have completed the construction of the result.
	// This yields significant speedups (up to +100%) in cases where
	// the result length is large (roughly, over L2 cache size).
	const chunkLimit = 8 * 1024
	chunkMax := n

}
</pre>

<p>
is guaranteed to print <code>"hello, world"</code>.  The write to <code>a</code>
is sequenced before the send on <code>c</code>, which is synchronized before
the corresponding receive on <code>c</code> completes, which is sequenced before
the <code>print</code>.
</p>

<p class="rule">
The closing of a channel is synchronized before a receive that returns a zero value
because the channel is closed.
</p>

<p>

		return 1, err
	}

	if goarch := os.Getenv("GOARCH"); goarch == "arm64" {
		err = runOnDevice(appdir)
	} else {
		err = runOnSimulator(appdir)
	}
	if err != nil {
		// If the lldb driver completed with an exit code, use that.
		if err, ok := err.(*exec.ExitError); ok {
			if ws, ok := err.Sys().(interface{ ExitStatus() int }); ok {
				return ws.ExitStatus(), nil
			}
		}
		return 1, err
	}