Re: [LTP] [PATCH 1/2] m4: mprotect04: Replace __builtin___clear_cache with __clear_cache

[Andrea Cervesato via ltp <ltp@lists.linux.it>]

Hi!

On Sun Oct 12, 2025 at 9:40 PM CEST, Petr Vorel wrote:
> __clear_cache() should be quite common now and we already use it in
> hugemmap15.c. Convert autotools m4 check to detect it.
>
> Signed-off-by: Petr Vorel <petr.vorel@gmail.com>
> ---
>  configure.ac                                  |  2 +-
>  m4/ltp-builtin_clear_cache.m4                 | 19 ------------------
>  m4/ltp-clear_cache.m4                         | 20 +++++++++++++++++++
>  .../kernel/syscalls/mprotect/mprotect04.c     |  7 +++----
>  4 files changed, 24 insertions(+), 24 deletions(-)
>  delete mode 100644 m4/ltp-builtin_clear_cache.m4
>  create mode 100644 m4/ltp-clear_cache.m4
>
> diff --git a/configure.ac b/configure.ac
> index 0480f46ca2..461fa2b577 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -393,9 +393,9 @@ AC_CONFIG_COMMANDS([syscalls.h], [cd ${ac_top_srcdir}/include/lapi/syscalls; ./g
>  # NOTE: don't create custom functions for simple checks, put them into this file
>  LTP_CHECK_ACL_SUPPORT
>  LTP_CHECK_ATOMIC_MEMORY_MODEL
> -LTP_CHECK_BUILTIN_CLEAR_CACHE
>  LTP_CHECK_CAPABILITY_SUPPORT
>  LTP_CHECK_CC_WARN_OLDSTYLE
> +LTP_CHECK_CLEAR_CACHE
>  LTP_CHECK_CRYPTO
>  LTP_CHECK_FORTIFY_SOURCE
>  LTP_CHECK_KERNEL_DEVEL
> diff --git a/m4/ltp-builtin_clear_cache.m4 b/m4/ltp-builtin_clear_cache.m4
> deleted file mode 100644
> index 86e1cfc914..0000000000
> --- a/m4/ltp-builtin_clear_cache.m4
> +++ /dev/null
> @@ -1,19 +0,0 @@
> -dnl SPDX-License-Identifier: GPL-2.0-or-later
> -dnl Copyright (c) Linux Test Project, 2016
> -
> -AC_DEFUN([LTP_CHECK_BUILTIN_CLEAR_CACHE],[
> -	AC_MSG_CHECKING([for __builtin___clear_cache])
> -	AC_LINK_IFELSE([AC_LANG_SOURCE([[
> -int main(void) {
> -	char arr[16];
> -	__builtin___clear_cache(arr, arr + sizeof(arr));
> -        return 0;
> -}]])],[has_bcc="yes"])
> -
> -if test "x$has_bcc" = xyes; then
> -	AC_DEFINE(HAVE_BUILTIN_CLEAR_CACHE,1,[Define to 1 if you have __builtin___clear_cache])
> -	AC_MSG_RESULT(yes)
> -else
> -	AC_MSG_RESULT(no)
> -fi
> -])
> diff --git a/m4/ltp-clear_cache.m4 b/m4/ltp-clear_cache.m4
> new file mode 100644
> index 0000000000..99c6a1b653
> --- /dev/null
> +++ b/m4/ltp-clear_cache.m4
> @@ -0,0 +1,20 @@
> +dnl SPDX-License-Identifier: GPL-2.0-or-later
> +dnl Copyright (c) Linux Test Project, 2016
> +dnl Copyright (c) Linux Test Project, 2025
> +
> +AC_DEFUN([LTP_CHECK_CLEAR_CACHE],[
> +	AC_MSG_CHECKING([for __clear_cache])
> +	AC_LINK_IFELSE([AC_LANG_SOURCE([[
> +int main(void) {
> +	char arr[16];
> +	__clear_cache(arr, arr + sizeof(arr));
> +        return 0;
> +}]])],[has_clear_cache="yes"])
> +
> +if test "x$has_clear_cache" = xyes; then
> +	AC_DEFINE(HAVE_CLEAR_CACHE, 1, [Define to 1 if you have __clear_cache])
> +	AC_MSG_RESULT(yes)
> +else
> +	AC_MSG_RESULT(no)
> +fi
> +])
> diff --git a/testcases/kernel/syscalls/mprotect/mprotect04.c b/testcases/kernel/syscalls/mprotect/mprotect04.c
> index 6c7f6bd017..fa4d3be4ba 100644
> --- a/testcases/kernel/syscalls/mprotect/mprotect04.c
> +++ b/testcases/kernel/syscalls/mprotect/mprotect04.c
> @@ -152,11 +152,10 @@ static int page_present(void *p)
>  
>  static void clear_cache(void *start, int len)
>  {
> -#if HAVE_BUILTIN_CLEAR_CACHE == 1
> -	__builtin___clear_cache(start, start + len);
> +#ifdef HAVE_CLEAR_CACHE

I'm not 100% sure if it's a good idea to rename HAVE_BUILTIN_CLEAR_CACHE
to HAVE_CLEAR_CACHE, since this syntax is often used inside tests to
check if we have missing syscalls/functions inside libc implementation.

I would keep HAVE_BUILTIN_CLEAR_CACHE anyway in this case, since it's a
strictly compiler related feature.

> +	__clear_cache(start, start + len);
>  #else
> -	tst_brkm(TCONF, cleanup,
> -		"compiler doesn't have __builtin___clear_cache()");
> +	tst_brkm(TCONF, cleanup, "compiler doesn't have __clear_cache()");
>  #endif
>  }
>  

-- 
Andrea Cervesato
SUSE QE Automation Engineer Linux
andrea.cervesato@suse.com


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