libc: add clang FORTIFY support

This patch adds clang-style FORTIFY to Bionic. For more information on
FORTIFY, please see https://goo.gl/8HS2dW . This implementation works
for versions of clang that don't support diagnose_if, so please see the
"without diagnose_if" sections. We plan to swap to a diagnose_if-based
FORTIFY later this year (since it doesn't really add any features; it
just simplifies the implementation a lot, and it gives us much prettier
diagnostics)

Bug: 32073964
Test: Builds on angler, bullhead, marlin, sailfish. Bionic CTS tests
pass on Angler and Bullhead.

Change-Id: I607aecbeee81529709b1eee7bef5b0836151eb2b
diff --git a/libc/include/string.h b/libc/include/string.h
index 3e52f48..38595b2 100644
--- a/libc/include/string.h
+++ b/libc/include/string.h
@@ -47,18 +47,23 @@
 #endif
 
 void* memccpy(void* _Nonnull __restrict, const void* _Nonnull __restrict, int, size_t);
-void* memchr(const void* _Nonnull, int, size_t) __attribute_pure__;
-void* memrchr(const void* _Nonnull, int, size_t) __attribute_pure__;
+void* memchr(const void* _Nonnull, int, size_t) __attribute_pure__ __overloadable
+        __RENAME_CLANG(memchr);
+void* memrchr(const void* _Nonnull, int, size_t) __attribute_pure__ __overloadable
+        __RENAME_CLANG(memrchr);
 int memcmp(const void* _Nonnull, const void* _Nonnull, size_t) __attribute_pure__;
-void* memcpy(void* _Nonnull __restrict, const void* _Nonnull __restrict, size_t);
+void* memcpy(void* _Nonnull __restrict, const void* _Nonnull __restrict, size_t)
+        __overloadable __RENAME_CLANG(memcpy);
 #if defined(__USE_GNU)
 void* mempcpy(void* _Nonnull __restrict, const void* _Nonnull __restrict, size_t) __INTRODUCED_IN(23);
 #endif
-void* memmove(void* _Nonnull, const void* _Nonnull, size_t);
-void* memset(void* _Nonnull, int, size_t);
+void* memmove(void* _Nonnull, const void* _Nonnull, size_t) __overloadable
+        __RENAME_CLANG(memmove);
+void* memset(void* _Nonnull, int, size_t) __overloadable __RENAME_CLANG(memset);
 void* memmem(const void* _Nonnull, size_t, const void* _Nonnull, size_t) __attribute_pure__;
 
-char* strchr(const char* _Nonnull, int) __attribute_pure__;
+char* strchr(const char* _Nonnull, int) __attribute_pure__ __overloadable
+        __RENAME_CLANG(strchr);
 char* __strchr_chk(const char* _Nonnull, int, size_t) __INTRODUCED_IN(18);
 #if defined(__USE_GNU)
 #if defined(__cplusplus)
@@ -69,16 +74,21 @@
 #endif
 #endif
 
-char* strrchr(const char* _Nonnull, int) __attribute_pure__;
+char* strrchr(const char* _Nonnull, int) __attribute_pure__ __overloadable
+        __RENAME_CLANG(strrchr);
 char* __strrchr_chk(const char* _Nonnull, int, size_t) __INTRODUCED_IN(18);
 
-size_t strlen(const char* _Nonnull) __attribute_pure__;
+size_t strlen(const char* _Nonnull) __attribute_pure__ __overloadable
+        __RENAME_CLANG(strlen);
 size_t __strlen_chk(const char* _Nonnull, size_t) __INTRODUCED_IN(17);
-int strcmp(const char* _Nonnull, const char* _Nonnull) __attribute_pure__;
-char* stpcpy(char* _Nonnull __restrict, const char* _Nonnull__restrict) __INTRODUCED_IN(21);
-char* strcpy(char* _Nonnull __restrict, const char* _Nonnull __restrict);
-char* strcat(char* _Nonnull __restrict, const char* _Nonnull __restrict);
 
+int strcmp(const char* _Nonnull, const char* _Nonnull) __attribute_pure__;
+char* stpcpy(char* _Nonnull __restrict, const char* _Nonnull __restrict)
+        __overloadable __RENAME_CLANG(stpcpy) __INTRODUCED_IN(21);
+char* strcpy(char* _Nonnull __restrict, const char* _Nonnull __restrict)
+        __overloadable __RENAME_CLANG(strcpy);
+char* strcat(char* _Nonnull __restrict, const char* _Nonnull __restrict)
+        __overloadable __RENAME_CLANG(strcat);
 char* strdup(const char* _Nonnull);
 
 char* strstr(const char* _Nonnull, const char* _Nonnull) __attribute_pure__;
@@ -95,14 +105,19 @@
 #endif
 
 size_t strnlen(const char* _Nonnull, size_t) __attribute_pure__;
-char* strncat(char* _Nonnull __restrict, const char* _Nonnull __restrict, size_t);
+char* strncat(char* _Nonnull __restrict, const char* _Nonnull __restrict, size_t)
+        __overloadable __RENAME_CLANG(strncat);
 char* strndup(const char* _Nonnull, size_t);
 int strncmp(const char* _Nonnull, const char* _Nonnull, size_t) __attribute_pure__;
-char* stpncpy(char* _Nonnull __restrict, const char* _Nonnull __restrict, size_t) __INTRODUCED_IN(21);
-char* strncpy(char* _Nonnull __restrict, const char* _Nonnull __restrict, size_t);
+char* stpncpy(char* _Nonnull __restrict, const char* _Nonnull __restrict, size_t)
+        __overloadable __RENAME_CLANG(stpncpy) __INTRODUCED_IN(21);
+char* strncpy(char* _Nonnull __restrict, const char* _Nonnull __restrict, size_t)
+        __overloadable __RENAME_CLANG(strncpy);
 
-size_t strlcat(char* _Nonnull __restrict, const char* _Nonnull __restrict, size_t);
-size_t strlcpy(char* _Nonnull __restrict, const char* _Nonnull __restrict, size_t);
+size_t strlcat(char* _Nonnull __restrict, const char* _Nonnull __restrict, size_t)
+        __overloadable __RENAME_CLANG(strlcat);
+size_t strlcpy(char* _Nonnull __restrict, const char* _Nonnull __restrict, size_t)
+        __overloadable __RENAME_CLANG(strlcpy);
 
 size_t strcspn(const char* _Nonnull, const char* _Nonnull) __attribute_pure__;
 char* strpbrk(const char* _Nonnull, const char* _Nonnull) __attribute_pure__;
@@ -135,29 +150,287 @@
 #endif
 
 void* __memchr_chk(const void* _Nonnull, int, size_t, size_t) __INTRODUCED_IN(23);
-__errordecl(__memchr_buf_size_error, "memchr called with size bigger than buffer");
-
 void* __memrchr_chk(const void* _Nonnull, int, size_t, size_t) __INTRODUCED_IN(23);
-__errordecl(__memrchr_buf_size_error, "memrchr called with size bigger than buffer");
-void* __memrchr_real(const void* _Nonnull, int, size_t) __RENAME(memrchr);
-
 char* __stpncpy_chk2(char* _Nonnull __restrict, const char* _Nonnull __restrict, size_t, size_t, size_t)
   __INTRODUCED_IN(21);
 char* __strncpy_chk2(char* _Nonnull __restrict, const char* _Nonnull __restrict, size_t, size_t, size_t)
   __INTRODUCED_IN(21);
-size_t __strlcpy_real(char* _Nonnull __restrict, const char* _Nonnull __restrict, size_t) __RENAME(strlcpy);
 size_t __strlcpy_chk(char* _Nonnull __restrict, const char* _Nonnull __restrict, size_t, size_t) __INTRODUCED_IN(17);
-size_t __strlcat_real(char* _Nonnull __restrict, const char* _Nonnull __restrict, size_t) __RENAME(strlcat);
 size_t __strlcat_chk(char* _Nonnull __restrict, const char* _Nonnull __restrict, size_t, size_t) __INTRODUCED_IN(17);
 
+/* Only used with FORTIFY, but some headers that need it undef FORTIFY, so we
+ * have the definition out here.
+ */
+struct __bionic_zero_size_is_okay_t {};
+
 #if defined(__BIONIC_FORTIFY)
+// These can share their implementation between gcc and clang with minimal
+// trickery...
+#if __ANDROID_API__ >= __ANDROID_API_J_MR1__
+__BIONIC_FORTIFY_INLINE
+void* memcpy(void* _Nonnull __restrict const dst __pass_object_size,
+        const void* _Nonnull __restrict src, size_t copy_amount) __overloadable {
+    return __builtin___memcpy_chk(dst, src, copy_amount, __bos0(dst));
+}
+
+__BIONIC_FORTIFY_INLINE
+void* memmove(void* const _Nonnull dst __pass_object_size,
+        const void* _Nonnull src, size_t len) __overloadable {
+    return __builtin___memmove_chk(dst, src, len, __bos0(dst));
+}
+#endif /* __ANDROID_API__ >= __ANDROID_API_J_MR1__ */
+
+#if __ANDROID_API__ >= __ANDROID_API_L__
+__BIONIC_FORTIFY_INLINE
+char* stpcpy(char* _Nonnull __restrict const dst __pass_object_size,
+        const char* _Nonnull __restrict src) __overloadable {
+    return __builtin___stpcpy_chk(dst, src, __bos(dst));
+}
+#endif /* __ANDROID_API__ >= __ANDROID_API_L__ */
+
+#if __ANDROID_API__ >= __ANDROID_API_J_MR1__
+__BIONIC_FORTIFY_INLINE
+char* strcpy(char* _Nonnull __restrict const dst __pass_object_size,
+        const char* _Nonnull __restrict src) __overloadable {
+    return __builtin___strcpy_chk(dst, src, __bos(dst));
+}
+#endif /* __ANDROID_API__ >= __ANDROID_API_J_MR1__ */
+
+__BIONIC_FORTIFY_INLINE
+char* strcat(char* _Nonnull __restrict const dst __pass_object_size,
+        const char* _Nonnull __restrict src) __overloadable {
+    return __builtin___strcat_chk(dst, src, __bos(dst));
+}
+
+__BIONIC_FORTIFY_INLINE
+char* strncat(char* const _Nonnull __restrict dst __pass_object_size,
+        const char* _Nonnull __restrict src, size_t n) __overloadable {
+    return __builtin___strncat_chk(dst, src, n, __bos(dst));
+}
+
+__BIONIC_FORTIFY_INLINE
+void* memset(void* const _Nonnull s __pass_object_size, int c, size_t n)
+        __overloadable {
+    return __builtin___memset_chk(s, c, n, __bos0(s));
+}
+
+
+#if defined(__clang__)
+
+#define __error_if_overflows_dst(name, dst, n, what) \
+    __enable_if(__bos0(dst) != __BIONIC_FORTIFY_UNKNOWN_SIZE && \
+                __bos0(dst) < (n), "selected when the buffer is too small") \
+    __errorattr(#name " called with " what " bigger than buffer")
+
+/*
+ * N.B. _Nonnull isn't necessary on params, since these functions just emit
+ * errors.
+ */
+__BIONIC_ERROR_FUNCTION_VISIBILITY
+void* memcpy(void* dst, const void* src, size_t copy_amount) __overloadable
+        __error_if_overflows_dst(memcpy, dst, copy_amount, "size");
+
+__BIONIC_ERROR_FUNCTION_VISIBILITY
+void* memmove(void *dst, const void* src, size_t len) __overloadable
+        __error_if_overflows_dst(memmove, dst, len, "size");
+
+__BIONIC_ERROR_FUNCTION_VISIBILITY
+void* memset(void* s, int c, size_t n) __overloadable
+        __error_if_overflows_dst(memset, s, n, "size");
+
+__BIONIC_ERROR_FUNCTION_VISIBILITY
+char* stpcpy(char* dst, const char* src) __overloadable
+        __error_if_overflows_dst(stpcpy, dst, __builtin_strlen(src), "string");
+
+__BIONIC_ERROR_FUNCTION_VISIBILITY
+char* strcpy(char* dst, const char* src) __overloadable
+        __error_if_overflows_dst(strcpy, dst, __builtin_strlen(src), "string");
 
 #if __ANDROID_API__ >= __ANDROID_API_M__
 __BIONIC_FORTIFY_INLINE
-void* memchr(const void* s, int c, size_t n) {
+void* memchr(const void* const _Nonnull s __pass_object_size, int c, size_t n)
+        __overloadable {
     size_t bos = __bos(s);
 
-#if !defined(__clang__)
+    if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
+        return __builtin_memchr(s, c, n);
+    }
+
+    return __memchr_chk(s, c, n, bos);
+}
+
+__BIONIC_FORTIFY_INLINE
+void* memrchr(const void* const _Nonnull s __pass_object_size, int c, size_t n)
+        __overloadable {
+    size_t bos = __bos(s);
+
+    if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
+        return __call_bypassing_fortify(memrchr)(s, c, n);
+    }
+
+    return __memrchr_chk(s, c, n, bos);
+}
+#endif /* __ANDROID_API__ >= __ANDROID_API_M__ */
+
+#if __ANDROID_API__ >= __ANDROID_API_L__
+__BIONIC_FORTIFY_INLINE
+char* stpncpy(char* __restrict const _Nonnull dst __pass_object_size,
+        const char* __restrict const _Nonnull src __pass_object_size,
+        size_t n) __overloadable {
+    size_t bos_dst = __bos(dst);
+    size_t bos_src = __bos(src);
+
+    /* Ignore dst size checks; they're handled in strncpy_chk */
+    if (bos_src == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
+        return __builtin___stpncpy_chk(dst, src, n, bos_dst);
+    }
+
+    return __stpncpy_chk2(dst, src, n, bos_dst, bos_src);
+}
+#endif /* __ANDROID_API__ >= __ANDROID_API_L__ */
+
+#if __ANDROID_API__ >= __ANDROID_API_J_MR1__
+__BIONIC_FORTIFY_INLINE
+char* strncpy(char* __restrict const _Nonnull dst __pass_object_size,
+        const char* __restrict const _Nonnull src __pass_object_size,
+        size_t n) __overloadable {
+    size_t bos_dst = __bos(dst);
+    size_t bos_src = __bos(src);
+
+    /* Ignore dst size checks; they're handled in strncpy_chk */
+    if (bos_src == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
+        return __builtin___strncpy_chk(dst, src, n, bos_dst);
+    }
+
+    return __strncpy_chk2(dst, src, n, bos_dst, bos_src);
+}
+
+__BIONIC_FORTIFY_INLINE
+size_t strlcpy(char* const _Nonnull __restrict dst __pass_object_size,
+        const char *_Nonnull __restrict src, size_t size) __overloadable {
+    size_t bos = __bos(dst);
+
+    if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
+        return __call_bypassing_fortify(strlcpy)(dst, src, size);
+    }
+
+    return __strlcpy_chk(dst, src, size, bos);
+}
+
+__BIONIC_FORTIFY_INLINE
+size_t strlcat(char* const _Nonnull __restrict dst __pass_object_size,
+        const char* _Nonnull __restrict src, size_t size) __overloadable {
+    size_t bos = __bos(dst);
+
+    if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
+        return __call_bypassing_fortify(strlcat)(dst, src, size);
+    }
+
+    return __strlcat_chk(dst, src, size, bos);
+}
+
+/*
+ * If we can evaluate the size of s at compile-time, just call __builtin_strlen
+ * on it directly. This makes it way easier for compilers to fold things like
+ * strlen("Foo") into a constant, as users would expect. -1ULL is chosen simply
+ * because it's large.
+ */
+__BIONIC_FORTIFY_INLINE
+size_t strlen(const char* const _Nonnull s __pass_object_size)
+        __overloadable __enable_if(__builtin_strlen(s) != -1ULL,
+                                   "enabled if s is a known good string.") {
+    return __builtin_strlen(s);
+}
+
+__BIONIC_FORTIFY_INLINE
+size_t strlen(const char* const _Nonnull s __pass_object_size_n(0))
+        __overloadable {
+    size_t bos = __bos0(s);
+
+    if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
+        return __builtin_strlen(s);
+    }
+
+    // return __builtin_strlen(s);
+    return __strlen_chk(s, bos);
+}
+#endif /* __ANDROID_API__ >= __ANDROID_API_J_MR1__ */
+
+#if  __ANDROID_API__ >= __ANDROID_API_J_MR2__
+__BIONIC_FORTIFY_INLINE
+char* strchr(const char* const _Nonnull s __pass_object_size_n(0), int c)
+        __overloadable {
+    size_t bos = __bos0(s);
+
+    if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
+        return __builtin_strchr(s, c);
+    }
+
+    // return __builtin_strchr(s, c);
+    return __strchr_chk(s, c, bos);
+}
+
+__BIONIC_FORTIFY_INLINE
+char* strrchr(const char* const _Nonnull s __pass_object_size, int c)
+        __overloadable {
+    size_t bos = __bos(s);
+
+    if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
+        return __builtin_strrchr(s, c);
+    }
+
+    return __strrchr_chk(s, c, bos);
+}
+#endif /* __ANDROID_API__ >= __ANDROID_API_J_MR2__ */
+
+/* In *many* cases, memset(foo, sizeof(foo), 0) is a mistake where the user has
+ * flipped the size + value arguments. However, there may be cases (e.g. with
+ * macros) where it's okay for the size to fold to zero. We should warn on this,
+ * but we should also provide a FORTIFY'ed escape hatch.
+ */
+__BIONIC_ERROR_FUNCTION_VISIBILITY
+void* memset(void* _Nonnull s, int c, size_t n,
+             struct __bionic_zero_size_is_okay_t ok)
+        __overloadable
+        __error_if_overflows_dst(memset, s, n, "size");
+
+__BIONIC_FORTIFY_INLINE
+void* memset(void* const _Nonnull s __pass_object_size, int c, size_t n,
+             struct __bionic_zero_size_is_okay_t ok __attribute__((unused)))
+        __overloadable {
+    return __builtin___memset_chk(s, c, n, __bos0(s));
+}
+
+extern struct __bionic_zero_size_is_okay_t __bionic_zero_size_is_okay;
+/* We verify that `c` is non-zero, because as pointless as memset(foo, 0, 0) is,
+ * flipping size + count will do nothing.
+ */
+__BIONIC_ERROR_FUNCTION_VISIBILITY
+void* memset(void* _Nonnull s, int c, size_t n) __overloadable
+        __enable_if(c && !n, "selected when we'll set zero bytes")
+        __RENAME_CLANG(memset)
+        __warnattr_real("will set 0 bytes; maybe the arguments got flipped? "
+                        "(Add __bionic_zero_size_is_okay as a fourth argument "
+                        "to silence this.)");
+
+#undef __error_zero_size
+#undef __error_if_overflows_dst
+#else // defined(__clang__)
+extern char* __strncpy_real(char* __restrict, const char*, size_t) __RENAME(strcpy);
+extern void* __memrchr_real(const void*, int, size_t) __RENAME(memrchr);
+extern size_t __strlcpy_real(char* __restrict, const char* __restrict, size_t)
+    __RENAME(strlcpy);
+extern size_t __strlcat_real(char* __restrict, const char* __restrict, size_t)
+    __RENAME(strlcat);
+
+__errordecl(__memchr_buf_size_error, "memchr called with size bigger than buffer");
+__errordecl(__memrchr_buf_size_error, "memrchr called with size bigger than buffer");
+
+#if __ANDROID_API__ >= __ANDROID_API_M__
+__BIONIC_FORTIFY_INLINE
+void* memchr(const void *_Nonnull s __pass_object_size, int c, size_t n) {
+    size_t bos = __bos(s);
+
     if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
         return __builtin_memchr(s, c, n);
     }
@@ -169,7 +442,6 @@
     if (__builtin_constant_p(n) && (n <= bos)) {
         return __builtin_memchr(s, c, n);
     }
-#endif
 
     return __memchr_chk(s, c, n, bos);
 }
@@ -178,7 +450,6 @@
 void* memrchr(const void* s, int c, size_t n) {
     size_t bos = __bos(s);
 
-#if !defined(__clang__)
     if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
         return __memrchr_real(s, c, n);
     }
@@ -190,38 +461,11 @@
     if (__builtin_constant_p(n) && (n <= bos)) {
         return __memrchr_real(s, c, n);
     }
-#endif
 
     return __memrchr_chk(s, c, n, bos);
 }
 #endif /* __ANDROID_API__ >= __ANDROID_API_M__ */
 
-#if __ANDROID_API__ >= __ANDROID_API_J_MR1__
-__BIONIC_FORTIFY_INLINE
-void* memcpy(void* _Nonnull __restrict dst, const void* _Nonnull __restrict src, size_t copy_amount) {
-    return __builtin___memcpy_chk(dst, src, copy_amount, __bos0(dst));
-}
-
-__BIONIC_FORTIFY_INLINE
-void* memmove(void* _Nonnull dst, const void* _Nonnull src, size_t len) {
-    return __builtin___memmove_chk(dst, src, len, __bos0(dst));
-}
-#endif /* __ANDROID_API__ >= __ANDROID_API_J_MR1__ */
-
-#if __ANDROID_API__ >= __ANDROID_API_L__
-__BIONIC_FORTIFY_INLINE
-char* stpcpy(char* _Nonnull __restrict dst, const char* _Nonnull __restrict src) {
-    return __builtin___stpcpy_chk(dst, src, __bos(dst));
-}
-#endif /* __ANDROID_API__ >= __ANDROID_API_L__ */
-
-#if __ANDROID_API__ >= __ANDROID_API_J_MR1__
-__BIONIC_FORTIFY_INLINE
-char* strcpy(char* _Nonnull __restrict dst, const char* _Nonnull __restrict src) {
-    return __builtin___strcpy_chk(dst, src, __bos(dst));
-}
-#endif /* __ANDROID_API__ >= __ANDROID_API_J_MR1__ */
-
 #if __ANDROID_API__ >= __ANDROID_API_L__
 __BIONIC_FORTIFY_INLINE
 char* stpncpy(char* _Nonnull __restrict dst, const char* _Nonnull __restrict src, size_t n) {
@@ -250,7 +494,7 @@
     size_t bos_src = __bos(src);
 
     if (bos_src == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
-        return __builtin___strncpy_chk(dst, src, n, bos_dst);
+        return __strncpy_real(dst, src, n);
     }
 
     if (__builtin_constant_p(n) && (n <= bos_src)) {
@@ -268,25 +512,10 @@
 
 #if __ANDROID_API__ >= __ANDROID_API_J_MR1__
 __BIONIC_FORTIFY_INLINE
-char* strcat(char* _Nonnull __restrict dst, const char* _Nonnull __restrict src) {
-    return __builtin___strcat_chk(dst, src, __bos(dst));
-}
-
-__BIONIC_FORTIFY_INLINE
-char *strncat(char* _Nonnull __restrict dst, const char* _Nonnull __restrict src, size_t n) {
-    return __builtin___strncat_chk(dst, src, n, __bos(dst));
-}
-
-__BIONIC_FORTIFY_INLINE
-void* memset(void* _Nonnull s, int c, size_t n) {
-    return __builtin___memset_chk(s, c, n, __bos0(s));
-}
-
-__BIONIC_FORTIFY_INLINE
-size_t strlcpy(char* _Nonnull __restrict dst, const char* _Nonnull __restrict src, size_t size) {
+size_t strlcpy(char* _Nonnull __restrict dst __pass_object_size,
+        const char* _Nonnull __restrict src, size_t size) {
     size_t bos = __bos(dst);
 
-#if !defined(__clang__)
     // Compiler doesn't know destination size. Don't call __strlcpy_chk
     if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
         return __strlcpy_real(dst, src, size);
@@ -297,17 +526,14 @@
     if (__builtin_constant_p(size) && (size <= bos)) {
         return __strlcpy_real(dst, src, size);
     }
-#endif /* !defined(__clang__) */
 
     return __strlcpy_chk(dst, src, size, bos);
 }
 
-
 __BIONIC_FORTIFY_INLINE
 size_t strlcat(char* _Nonnull __restrict dst, const char* _Nonnull __restrict src, size_t size) {
     size_t bos = __bos(dst);
 
-#if !defined(__clang__)
     // Compiler doesn't know destination size. Don't call __strlcat_chk
     if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
         return __strlcat_real(dst, src, size);
@@ -318,16 +544,14 @@
     if (__builtin_constant_p(size) && (size <= bos)) {
         return __strlcat_real(dst, src, size);
     }
-#endif /* !defined(__clang__) */
 
     return __strlcat_chk(dst, src, size, bos);
 }
 
 __BIONIC_FORTIFY_INLINE
-size_t strlen(const char* _Nonnull s) {
+size_t strlen(const char* _Nonnull s) __overloadable {
     size_t bos = __bos(s);
 
-#if !defined(__clang__)
     // Compiler doesn't know destination size. Don't call __strlen_chk
     if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
         return __builtin_strlen(s);
@@ -337,7 +561,6 @@
     if (__builtin_constant_p(slen)) {
         return slen;
     }
-#endif /* !defined(__clang__) */
 
     return __strlen_chk(s, bos);
 }
@@ -348,7 +571,6 @@
 char* strchr(const char* _Nonnull s, int c) {
     size_t bos = __bos(s);
 
-#if !defined(__clang__)
     // Compiler doesn't know destination size. Don't call __strchr_chk
     if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
         return __builtin_strchr(s, c);
@@ -358,7 +580,6 @@
     if (__builtin_constant_p(slen) && (slen < bos)) {
         return __builtin_strchr(s, c);
     }
-#endif /* !defined(__clang__) */
 
     return __strchr_chk(s, c, bos);
 }
@@ -367,7 +588,6 @@
 char* strrchr(const char* _Nonnull s, int c) {
     size_t bos = __bos(s);
 
-#if !defined(__clang__)
     // Compiler doesn't know destination size. Don't call __strrchr_chk
     if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
         return __builtin_strrchr(s, c);
@@ -377,12 +597,11 @@
     if (__builtin_constant_p(slen) && (slen < bos)) {
         return __builtin_strrchr(s, c);
     }
-#endif /* !defined(__clang__) */
 
     return __strrchr_chk(s, c, bos);
 }
 #endif /* __ANDROID_API__ >= __ANDROID_API_J_MR2__ */
-
+#endif /* defined(__clang__) */
 #endif /* defined(__BIONIC_FORTIFY) */
 
 #if defined(__clang__)