diff --git a/libc/SYSCALLS.TXT b/libc/SYSCALLS.TXT
index 5f49c8c..e8dde7c 100644
--- a/libc/SYSCALLS.TXT
+++ b/libc/SYSCALLS.TXT
@@ -161,7 +161,7 @@
 int linkat(int, const char*, int, const char*, int)  all
 int mkdirat(int, const char*, mode_t)  all
 int mknodat(int, const char*, mode_t, dev_t)  all
-int readlinkat(int, const char*, char*, size_t)  all
+ssize_t readlinkat(int, const char*, char*, size_t)  all
 int renameat2(int, const char*, int, const char*, unsigned)  all
 int symlinkat(const char*, int, const char*)  all
 int unlinkat(int, const char*, int)   all
diff --git a/libc/include/bits/getentropy.h b/libc/include/bits/getentropy.h
new file mode 100644
index 0000000..a5a14f7
--- /dev/null
+++ b/libc/include/bits/getentropy.h
@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#pragma once
+
+/**
+ * @file bits/getentropy.h
+ * @brief The getentropy() function.
+ */
+
+#include <sys/cdefs.h>
+#include <sys/types.h>
+
+__BEGIN_DECLS
+
+/**
+ * [getentropy(3)](http://man7.org/linux/man-pages/man3/getentropy.3.html) fills the given buffer
+ * with random bytes.
+ *
+ * Returns 0 on success, and returns -1 and sets `errno` on failure.
+ *
+ * Available since API level 28.
+ *
+ * See also arc4random_buf() which is available in all API levels.
+ */
+int getentropy(void* _Nonnull __buffer, size_t __buffer_size) __wur __INTRODUCED_IN(28);
+
+__END_DECLS
diff --git a/libc/include/sys/cachectl.h b/libc/include/sys/cachectl.h
index fd775ee..b5fabe3 100644
--- a/libc/include/sys/cachectl.h
+++ b/libc/include/sys/cachectl.h
@@ -37,6 +37,8 @@
 
 __BEGIN_DECLS
 
+#if defined(__riscv)
+
 /**
  * Flag for __riscv_flush_icache() to indicate that only the current
  * thread's instruction cache needs to be flushed (rather than the
@@ -46,9 +48,12 @@
 
 /**
  * __riscv_flush_icache(2) flushes the instruction cache for the given range of addresses.
+ * The address range is currently (Linux 6.4) ignored, so both pointers may be null.
  *
  * Returns 0 on success, and returns -1 and sets `errno` on failure.
  */
-int __riscv_flush_icache(void* __start, void* __end, unsigned long __flags);
+int __riscv_flush_icache(void* _Nullable __start, void* _Nullable __end, unsigned long __flags);
+
+#endif
 
 __END_DECLS
diff --git a/libc/include/sys/random.h b/libc/include/sys/random.h
index 0251176..2ff5349 100644
--- a/libc/include/sys/random.h
+++ b/libc/include/sys/random.h
@@ -38,19 +38,9 @@
 
 #include <linux/random.h>
 
-__BEGIN_DECLS
+#include <bits/getentropy.h>
 
-/**
- * [getentropy(3)](http://man7.org/linux/man-pages/man3/getentropy.3.html) fills the given buffer
- * with random bytes.
- *
- * Returns 0 on success, and returns -1 and sets `errno` on failure.
- *
- * Available since API level 28.
- *
- * See also arc4random_buf() which is available in all API levels.
- */
-int getentropy(void* _Nonnull __buffer, size_t __buffer_size) __wur __INTRODUCED_IN(28);
+__BEGIN_DECLS
 
 /**
  * [getrandom(2)](http://man7.org/linux/man-pages/man2/getrandom.2.html) fills the given buffer
diff --git a/libc/include/unistd.h b/libc/include/unistd.h
index 9385264..dcad630 100644
--- a/libc/include/unistd.h
+++ b/libc/include/unistd.h
@@ -34,6 +34,7 @@
 #include <sys/select.h>
 
 #include <bits/fcntl.h>
+#include <bits/getentropy.h>
 #include <bits/getopt.h>
 #include <bits/ioctl.h>
 #include <bits/lockf.h>
diff --git a/tests/uchar_test.cpp b/tests/uchar_test.cpp
index 4dc6314..1936a8d 100644
--- a/tests/uchar_test.cpp
+++ b/tests/uchar_test.cpp
@@ -24,6 +24,22 @@
 #include <locale.h>
 #include <stdint.h>
 
+// Modern versions of UTF-8 (https://datatracker.ietf.org/doc/html/rfc3629 and
+// newer) explicitly disallow code points beyond U+10FFFF, which exclude all 5-
+// and 6-byte sequences. Earlier versions of UTF-8 allowed the wider range:
+// https://datatracker.ietf.org/doc/html/rfc2279.
+//
+// Bionic's unicode implementation was written after the high values were
+// excluded, so it has never supported them. Other implementations (at least
+// as of glibc 2.36), do support those sequences.
+#if defined(__ANDROID__) || defined(ANDROID_HOST_MUSL)
+constexpr bool kLibcSupportsLongUtf8Sequences = 0;
+#elif defined(__GLIBC__)
+constexpr bool kLibcSupportsLongUtf8Sequences = 1;
+#else
+#error kLibcSupportsLongUtf8Sequences must be configured for this platform
+#endif
+
 TEST(uchar, sizeof_uchar_t) {
   EXPECT_EQ(2U, sizeof(char16_t));
   EXPECT_EQ(4U, sizeof(char32_t));
@@ -146,10 +162,24 @@
   ASSERT_EQ(static_cast<char16_t>(0xdbea), out);
   ASSERT_EQ(4U, mbrtoc16(&out, "\xf4\x8a\xaf\x8d" "ef", 6, nullptr));
   ASSERT_EQ(static_cast<char16_t>(0xdfcd), out);
-  // Illegal 5-byte UTF-8.
+}
+
+TEST(uchar, mbrtoc16_long_sequences) {
+  ASSERT_STREQ("C.UTF-8", setlocale(LC_CTYPE, "C.UTF-8"));
+  uselocale(LC_GLOBAL_LOCALE);
+
+  char16_t out = u'\0';
   errno = 0;
-  ASSERT_EQ(static_cast<size_t>(-1), mbrtoc16(&out, "\xf8\xa1\xa2\xa3\xa4", 5, nullptr));
-  ASSERT_EQ(EILSEQ, errno);
+  auto result = mbrtoc16(&out, "\xf8\xa1\xa2\xa3\xa4", 5, nullptr);
+  if (kLibcSupportsLongUtf8Sequences) {
+    EXPECT_EQ(5U, result);
+    EXPECT_EQ(0, errno);
+    EXPECT_EQ(u'\uf94a', out);
+  } else {
+    EXPECT_EQ(static_cast<size_t>(-1), result);
+    EXPECT_EQ(EILSEQ, errno);
+    EXPECT_EQ(u'\0', out);
+  }
 }
 
 TEST(uchar, mbrtoc16_reserved_range) {