diff --git a/doc/go1.15.html b/doc/go1.15.html
index 448a507f6a..42687a4741 100644
--- a/doc/go1.15.html
+++ b/doc/go1.15.html
@@ -94,6 +94,16 @@ Do not send CLs removing the interior tags from such phrases.
   preemption.
 </p>
 
+<h3 id="386">386</h3>
+
+<p><!-- golang.org/issue/40255 -->
+  Go 1.15 is the last release to support x87-only floating-point
+  hardware (<code>GO386=387</code>). Future releases will require at
+  least SSE2 support on 386, raising Go's
+  minimum <code>GOARCH=386</code> requirement to the Intel Pentium 4
+  (released in 2000) or AMD Opteron/Athlon 64 (released in 2003).
+</p>
+
 <h2 id="tools">Tools</h2>
 
 <h3 id="go-command">Go command</h3>
@@ -376,6 +386,23 @@ Do not send CLs removing the interior tags from such phrases.
   documentation</a> for more information.
 </p>
 
+<h3 id="commonname">X.509 CommonName deprecation</h3>
+
+<p><!-- CL 231379 -->
+  The deprecated, legacy behavior of treating the <code>CommonName</code>
+  field on X.509 certificates as a host name when no Subject Alternative Names
+  are present is now disabled by default. It can be temporarily re-enabled by
+  adding the value <code>x509ignoreCN=0</code> to the <code>GODEBUG</code>
+  environment variable.
+</p>
+
+<p>
+  Note that if the <code>CommonName</code> is an invalid host name, it's always
+  ignored, regardless of <code>GODEBUG</code> settings. Invalid names include
+  those with any characters other than letters, digits, hyphens and underscores,
+  and those with empty labels or trailing dots.
+</p>
+
 <h3 id="minor_library_changes">Minor changes to the library</h3>
 
 <p>
@@ -513,15 +540,6 @@ Do not send CLs removing the interior tags from such phrases.
       certificates with trailing dots.
     </p>
 
-    <p><!-- CL 231379 -->
-      The deprecated, legacy behavior of treating the <code>CommonName</code>
-      field as a hostname when no Subject Alternative Names are present is now
-      disabled by default. It can be temporarily re-enabled by adding the value
-      <code>x509ignoreCN=0</code> to the <code>GODEBUG</code> environment
-      variable. If the <code>CommonName</code> is an invalid hostname, it's
-      always ignored.
-    </p>
-
     <p><!-- CL 217298 -->
       The new <a href="/pkg/crypto/x509/#CreateRevocationList"><code>CreateRevocationList</code></a>
       function and <a href="/pkg/crypto/x509/#RevocationList"><code>RevocationList</code></a> type
@@ -703,6 +721,16 @@ Do not send CLs removing the interior tags from such phrases.
   </dd>
 </dl><!-- math/big -->
 
+<dl id="math/cmplx"><dt><a href="/pkg/math/cmplx/">math/cmplx</a></dt>
+  <dd>
+    <p><!-- CL 220689 -->
+      The functions in this package were updated to conform to the C99 standard
+      (Annex G IEC 60559-compatible complex arithmetic) with respect to handling
+      of special arguments such as infinity, NaN and signed zero.
+    </p>
+  </dd>
+</dl><!-- math/cmplx-->
+
 <dl id="net"><dt><a href="/pkg/net/">net</a></dt>
   <dd>
     <p><!-- CL 228645 -->
diff --git a/src/runtime/os_linux_x86.go b/src/runtime/os_linux_x86.go
index d001e6ee59..97f870707d 100644
--- a/src/runtime/os_linux_x86.go
+++ b/src/runtime/os_linux_x86.go
@@ -7,7 +7,10 @@
 
 package runtime
 
-import "runtime/internal/atomic"
+import (
+	"runtime/internal/atomic"
+	"unsafe"
+)
 
 //go:noescape
 func uname(utsname *new_utsname) int
@@ -55,6 +58,36 @@ func osArchInit() {
 		return
 	}
 
+	if major == 5 && minor == 4 && patch < 2 {
+		// All 5.4 versions of Ubuntu are patched.
+		procVersion := []byte("/proc/version\000")
+		f := open(&procVersion[0], _O_RDONLY, 0)
+		if f >= 0 {
+			var buf [512]byte
+			p := noescape(unsafe.Pointer(&buf[0]))
+			n := read(f, p, int32(len(buf)))
+			closefd(f)
+
+			needle := []byte("Ubuntu")
+		contains:
+			for i, c := range buf[:n] {
+				if c != needle[0] {
+					continue
+				}
+				if int(n)-i < len(needle) {
+					break
+				}
+				for j, c2 := range needle {
+					if c2 != buf[i+j] {
+						continue contains
+					}
+				}
+				// This is an Ubuntu system.
+				return
+			}
+		}
+	}
+
 	if major == 5 && (minor == 2 || minor == 3 && patch < 15 || minor == 4 && patch < 2) {
 		gsignalInitQuirk = mlockGsignal
 		if m0.gsignal != nil {
diff --git a/test/fixedbugs/issue33308.go b/test/fixedbugs/issue33308.go
new file mode 100644
index 0000000000..b0fd6a450c
--- /dev/null
+++ b/test/fixedbugs/issue33308.go
@@ -0,0 +1,12 @@
+// errorcheck
+
+// Copyright 2020 The Go Authors. All rights reserved.  Use of this
+// source code is governed by a BSD-style license that can be found in
+// the LICENSE file.
+
+// Test that the compiler does not crash on a []byte conversion of an
+// untyped expression.
+package p
+
+var v uint
+var x = []byte((1 << v) + 1) // ERROR "cannot convert"