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/sys/cdefs.h b/libc/include/sys/cdefs.h
index dab252d..aa93c78 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -297,9 +297,12 @@
/* __BIONIC_FORTIFY_NONSTATIC_INLINE is pointless in GCC's FORTIFY */
# define __BIONIC_FORTIFY_INLINE extern __inline__ __always_inline __attribute__((gnu_inline)) __attribute__((__artificial__))
# endif
-# define __pass_object_size __pass_object_size_n(__bos_level)
-# define __pass_object_size0 __pass_object_size_n(0)
+#else
+/* Further increase sharing for some inline functions */
+# define __pass_object_size_n(n)
#endif
+#define __pass_object_size __pass_object_size_n(__bos_level)
+#define __pass_object_size0 __pass_object_size_n(0)
/* Used to support clangisms with FORTIFY. This isn't in the FORTIFY section
* because these change how symbols are emitted. The linker must be kept happy.