These functions are only available in the preamble, not in other C
files. The C code must not modify the contents of the pointer returned
by _GoStringPtr. Note that the string contents may not have a trailing
NUL byte.

As Go doesn't have support for C's union type in the general case,
C's union types are represented as a Go byte array with the same length.

Go structs cannot embed fields with C types.

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
connecting to servers with buggy HTTP/2 implementations.
These kinds of changes are unavoidable and
[permitted by the Go 1 compatibility rules](/doc/go1compat).
Even so, Go provides a mechanism called GODEBUG to
reduce the impact such changes have on Go developers
using newer toolchains to compile old code.

// Type flags for Header.Typeflag.
const (
	// Type '0' indicates a regular file.
	TypeReg = '0'

	// Deprecated: Use TypeReg instead.
	TypeRegA = '\x00'

	// Type '1' to '6' are header-only flags and may not have a data body.
	TypeLink    = '1' // Hard link
	TypeSymlink = '2' // Symbolic link
	TypeChar    = '3' // Character device node
	TypeBlock   = '4' // Block device node
	TypeDir     = '5' // Directory

		}
	}
	if haveConstant {
		p.back()
		if p.have(scanner.Float) {
			if prefix != '$' {
				p.errorf("floating-point constant must be an immediate")
			}
			a.Type = obj.TYPE_FCONST
			a.Val = p.floatExpr()
			// fmt.Printf("FCONST %s\n", obj.Dconv(&emptyProg, 0, a))
			p.expectOperandEnd()
			return
		}
		if p.have(scanner.String) {
			if prefix != '$' {

Care should be taken when using vector instructions to ensure that they are available at
runtime.
To use vector instructions a machine must have both the vector facility (bit 129 in the
facility list) and kernel support.
Without kernel support a vector instruction will have no effect (it will be equivalent
to a <code>NOP</code> instruction).
</p>

<p>
Addressing modes:
</p>

<ul>

<li>

	// 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

// invocation of F then behaves like a call to panic, terminating G's
// execution and running any deferred functions. This continues until all
// functions in the executing goroutine have stopped, in reverse order. At
// that point, the program is terminated with a non-zero exit code. This
// termination sequence is called panicking and can be controlled by the
// built-in function recover.
//

	}
	testValidHeader(&h, t)
}

// Issue 4393. It is valid to have an extra data header
// which contains no body.
func TestZeroLengthHeader(t *testing.T) {
	h := FileHeader{
		Name:   "extadata.txt",
		Method: Deflate,
		Extra: []byte{

				if strings.HasSuffix(hdr.Name, "/") {
					hdr.Typeflag = TypeDir // Legacy archives use trailing slash for directories
				} else {
					hdr.Typeflag = TypeReg
				}
			}

			// The extended headers may have updated the size.
			// Thus, setup the regFileReader again after merging PAX headers.
			if err := tr.handleRegularFile(hdr); err != nil {
				return nil, err
			}

must observe a value actually written to that location (perhaps by a concurrent executing goroutine)
and not yet overwritten.
These implementation constraints make Go more like Java or JavaScript,
in that most races have a limited number of outcomes,
and less like C and C++, where the meaning of any program with a race
is entirely undefined, and the compiler may do anything at all.