clang generates internal calls for some _chk symbol, so add internal
aliases for them, and stub some with rtld-stubbed-symbols to avoid
ld.so linker issues.

Reviewed-by: Sam James <sam@gentoo.org>

C23 makes various standard library functions, that return a pointer
into an input array, into macros that return a pointer to const when
the relevant argument passed to the macro is a pointer to const.  (The
requirement is for macros, with the existing function types applying
when macro expansion is suppressed.  When a null pointer constant is
passed, such as integer 0, that's the same as a pointer to non-const.)

Implement this feature.  This only applies to C, not C++, since such
macros are not an appropriate way of doing this for C++ and all the
affected functions other than bsearch have overloads to implement an
equivalent feature for C++ anyway.  Nothing is done to apply such a
change to any non-C23 functions with the same property of returning a
pointer into an input array.

The feature is also disabled when _LIBC is defined, since there are
various places in glibc that either redefine these identifiers as
macros, or define the functions themselves, and would need changing to
work in the presence of these macro definitions.  A natural question
is whether we should in fact change those places and not disable the
macro definitions for _LIBC.  If so, we'd need a solution for the
places in glibc that define the macro *before* including the relevant
header (in order in effect to disable the header declaration of the
function by renaming that declaration).

One testcase has #undef added to avoid conflicting with this feature
and another has const added; -Wno-discarded-qualifiers is added for
building zic (but could be removed once there's a new upstream tzcode
release that's const-safe with this C23 change and glibc has updated
to code from that new release).  Probably other places in glibc proper
would need const added if we remove the _LIBC conditionals.

Another question would be whether some GCC extension should be added
to support this feature better with macros that only expand each
argument once (as well as reducing duplication of diagnostics for bad
usages such as non-pointer and pointer-to-volatile-qualfied
arguments).

Tested for x86_64.

The warning is not supported by clang.

Reviewed-by: Sam James <sam@gentoo.org>

Add the C23 memset_explicit function to glibc.  Everything here is
closely based on the approach taken for explicit_bzero.  This includes
the bits that relate to internal uses of explicit_bzero within glibc
(although we don't currently have any such internal uses of
memset_explicit), and also includes the nonnull attribute (when we
move to nonnull_if_nonzero for various functions following C2y, this
function should be included in that change).

The function is declared both for __USE_MISC and for __GLIBC_USE (ISOC23)
(so by default not just for compilers defaulting to C23 mode).

Tested for x86_64 and x86.

Use __thread variables directly instead.  The macros do not save any
typing.  It seems unlikely that a future port will lack __thread
variable support.

Some of the __libc_tsd_* variables are referenced from assembler
files, so keep their names.  Previously, <libc-tls.h> included
<tls.h>, which in turn included <errno.h>, so a few direct includes
of <errno.h> are now required.

Reviewed-by: Frédéric Bérat <fberat@redhat.com>

Add a configure check for -Wno-fortify-source to suppress Clang warnings
on string/tester.c, like:

tester.c:385:10: error: 'strncat' size argument is too large; destination buffer has size 50, but size argument is 99 [-Werror,-Wfortify-source]
  385 |   check (strncat (one, "lmn", 99) == one, 1);   /* Returned value. */

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Sam James <sam@gentoo.org>

Add __attribute_optimization_barrier__ to disable inlining and cloning on a
function.  For Clang, expand it to

__attribute__ ((optnone))

Otherwise, expand it to

__attribute__ ((noinline, clone))

Co-Authored-By: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Sam James <sam@gentoo.org>

Without stack protector, inhibit_stack_protector is undefined during build:

In file included from <command-line>:
./../include/libc-symbols.h:665:3: error: expected ';' before '__typeof'
  665 |   __typeof (type_name) *name##_ifunc (__VA_ARGS__)
         \
      |   ^~~~~~~~
./../include/libc-symbols.h:676:3: note: in expansion of macro
'__ifunc_resolver'
  676 |   __ifunc_resolver (type_name, name, expr, init, static, __VA_ARGS__)
      |   ^~~~~~~~~~~~~~~~
./../include/libc-symbols.h:703:3: note: in expansion of macro '__ifunc_args'
  703 |   __ifunc_args (type_name, name, expr, init, arg)
      |   ^~~~~~~~~~~~
./../include/libc-symbols.h:790:3: note: in expansion of macro '__ifunc'
  790 |   __ifunc (redirected_name, name, expr, void, INIT_ARCH)
      |   ^~~~~~~
../sysdeps/x86_64/multiarch/memchr.c:29:1: note: in expansion of macro
'libc_ifunc_redirected'
   29 | libc_ifunc_redirected (__redirect_memchr, memchr, IFUNC_SELECTOR ());
      | ^~~~~~~~~~~~~~~~~~~~~

1. Fix a typo in include/libc-symbols.h to define inhibit_stack_protector
for build.
2. Don't include <config.h> in include/libc-symbols.h since it has been
included in include/libc-misc.h.
3. Change #include "libc-misc.h" to #include <libc-misc.h> in
string/test-string.h.

This fixes BZ #32494.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Sam James <sam@gentoo.org>

Add include/libc-misc.h to provide miscellaneous definitions for both
glibc build and test:

1. Move inhibit_stack_protector to libc-misc.h and add Clang support.
2. Add test_inhibit_stack_protector for glibc testing.
3. Move inhibit_loop_to_libcall to libc-misc.h.
4. Add test_cc_inhibit_loop_to_libcall to handle TEST_CC != CC and
replace inhibit_loop_to_libcall with test_cc_inhibit_loop_to_libcall
in glibc tests.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
Co-Authored-By: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Reviewed-by: Sam James <sam@gentoo.org>