libc: add const-correct string.h overloads
libcxx provides const-correct overloads for a few string.h functions.
These overloads use clang's enable_if attribute, so they're preferred
over our FORTIFY'ed equivalents.
This weakens _FORTIFY_SOURCE=2 when used with some of these functions,
since clang needs to see __pass_object_size in order to pass an accurate
result for __builtin_object_size(s, 1) at a callsite. Since those
functions don't have __pass_object_size on their params, clang can't do
that. This makes LLVM lower the __builtin_object_size calls, which means
we get the same result as __builtin_object_size(s, 0).
We have to provide all of the overloads in Bionic, since enable_if is
only used to disambiguate overloads with (otherwise) the same type. In
other words:
// overload 1
char *strchr(const char *, int s) __attribute__((enable_if(1, "")));
// overload 2
char *strchr(char *, int s);
void foo() {
char cs[1] = {};
strchr(static_cast<const char *>(cs), '\0'); // calls overload #1.
strchr(cs, '\0'); // calls overload #2.
}
Bug: 34747525
Test: m checkbuild on bullhead internal master + AOSP. vts -m
BionicUnitTests passes on both. Surprisingly, the only code that this
seems to break is contained in Bionic.
Change-Id: Ie406f42fb3d1c5bf940dc857889876fc39b57c90
diff --git a/libc/include/string.h b/libc/include/string.h
index 0cbd61c..2027231 100644
--- a/libc/include/string.h
+++ b/libc/include/string.h
@@ -366,7 +366,6 @@
return __builtin_strchr(s, c);
}
- // return __builtin_strchr(s, c);
return __strchr_chk(s, c, bos);
}
@@ -606,6 +605,92 @@
#endif /* defined(__clang__) */
#endif /* defined(__BIONIC_FORTIFY) */
+/* Const-correct overloads. Placed after FORTIFY so we call those functions, if possible. */
+#if defined(__cplusplus) && defined(__clang__)
+/*
+ * Use two enable_ifs so these overloads don't conflict with + are preferred over libcxx's. This can
+ * be reduced to 1 after libcxx recognizes that we have const-correct overloads.
+ */
+#define __prefer_this_overload __enable_if(true, "preferred overload") __enable_if(true, "")
+extern "C++" {
+inline __always_inline
+void* __bionic_memchr(const void* const _Nonnull s __pass_object_size, int c, size_t n) {
+ return memchr(s, c, n);
+}
+
+inline __always_inline
+const void* memchr(const void* const _Nonnull s __pass_object_size, int c, size_t n)
+ __prefer_this_overload {
+ return __bionic_memchr(s, c, n);
+}
+
+inline __always_inline
+void* memchr(void* const _Nonnull s __pass_object_size, int c, size_t n) __prefer_this_overload {
+ return __bionic_memchr(s, c, n);
+}
+
+inline __always_inline
+char* __bionic_strchr(const char* const _Nonnull s __pass_object_size, int c) {
+ return strchr(s, c);
+}
+
+inline __always_inline
+const char* strchr(const char* const _Nonnull s __pass_object_size, int c)
+ __prefer_this_overload {
+ return __bionic_strchr(s, c);
+}
+
+inline __always_inline
+char* strchr(char* const _Nonnull s __pass_object_size, int c)
+ __prefer_this_overload {
+ return __bionic_strchr(s, c);
+}
+
+inline __always_inline
+char* __bionic_strrchr(const char* const _Nonnull s __pass_object_size, int c) {
+ return strrchr(s, c);
+}
+
+inline __always_inline
+const char* strrchr(const char* const _Nonnull s __pass_object_size, int c) __prefer_this_overload {
+ return __bionic_strrchr(s, c);
+}
+
+inline __always_inline
+char* strrchr(char* const _Nonnull s __pass_object_size, int c) __prefer_this_overload {
+ return __bionic_strrchr(s, c);
+}
+
+/* Functions with no FORTIFY counterpart. */
+inline __always_inline
+char* __bionic_strstr(const char* _Nonnull h, const char* _Nonnull n) { return strstr(h, n); }
+
+inline __always_inline
+const char* strstr(const char* _Nonnull h, const char* _Nonnull n) __prefer_this_overload {
+ return __bionic_strstr(h, n);
+}
+
+inline __always_inline
+char* strstr(char* _Nonnull h, const char* _Nonnull n) __prefer_this_overload {
+ return __bionic_strstr(h, n);
+}
+
+inline __always_inline
+char* __bionic_strpbrk(const char* _Nonnull h, const char* _Nonnull n) { return strpbrk(h, n); }
+
+inline __always_inline
+char* strpbrk(char* _Nonnull h, const char* _Nonnull n) __prefer_this_overload {
+ return __bionic_strpbrk(h, n);
+}
+
+inline __always_inline
+const char* strpbrk(const char* _Nonnull h, const char* _Nonnull n) __prefer_this_overload {
+ return __bionic_strpbrk(h, n);
+}
+}
+#undef __prefer_this_overload
+#endif
+
#if defined(__clang__)
#pragma clang diagnostic pop
#endif