[PATCH 37/39] Suppress Clang -Wimplicit-fallthrough warnings

[Sam James]

"H.J. Lu" <hjl.tools@gmail.com> writes:

> Since Clang doesn't properly handle
>
> /* FALLTHROUGH */
>
> in elf/tst-align2.c nor
>
> /* fall through */
>
> in misc/tst-tsearch.c
>
> tst-align2.c:100:9: error: unannotated fall-through between switch labels [-Werror,-Wimplicit-fallthrough]
>   100 |         case 'A':
>       |         ^
> tst-align2.c:100:9: note: insert '__attribute__((fallthrough));' to silence this warning
>   100 |         case 'A':
>       |         ^
>       |         __attribute__((fallthrough));
> tst-align2.c:100:9: note: insert 'break;' to avoid fall-through
>   100 |         case 'A':
>       |         ^
>       |         break;
>
> suppress them when compiled with Clang.
>
> Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
> ---
>  configure     | 7 +++++++
>  configure.ac  | 7 +++++++
>  elf/Makefile  | 3 +++
>  misc/Makefile | 3 +++
>  4 files changed, 20 insertions(+)
>
> diff --git a/configure b/configure
> index 8e47743afb..103b5f2fb1 100755
> --- a/configure
> +++ b/configure
> @@ -8124,6 +8124,13 @@ fi
>  config_vars="$config_vars
>  cc-option-wimplicit-fallthrough = $libc_cv_cc_wimplicit_fallthrough"
>
> +if test -n "$libc_cv_test_cc_wimplicit_fallthrough"; then
> +  libc_cv_test_cc_wno_implicit_fallthrough="-Wno-implicit-fallthrough"
> +else
> +  libc_cv_test_cc_wno_implicit_fallthrough=
> +fi
> +config_vars="$config_vars
> +cc-option-wno-implicit-fallthrough = $libc_cv_test_cc_wno_implicit_fallthrough"
>
>  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for libgd" >&5
>  printf %s "checking for libgd... " >&6; }
> diff --git a/configure.ac b/configure.ac
> index d39e16b9ec..ec3992b3ed 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -1647,6 +1647,13 @@ LIBC_TRY_CC_AND_TEST_CC_OPTION([for -Wimplicit-fallthrough],
>  LIBC_CONFIG_VAR([cc-option-wimplicit-fallthrough],
>  		[$libc_cv_cc_wimplicit_fallthrough])
>  AC_SUBST(libc_cv_test_cc_wimplicit_fallthrough)
> +if test -n "$libc_cv_test_cc_wimplicit_fallthrough"; then
> +  libc_cv_test_cc_wno_implicit_fallthrough="-Wno-implicit-fallthrough"
> +else
> +  libc_cv_test_cc_wno_implicit_fallthrough=
> +fi
> +LIBC_CONFIG_VAR([cc-option-wno-implicit-fallthrough],
> +		[$libc_cv_test_cc_wno_implicit_fallthrough])
>
>  dnl Check whether we have the gd library available.
>  AC_MSG_CHECKING(for libgd)
> diff --git a/elf/Makefile b/elf/Makefile
> index 68fde4f226..edb08972c9 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -1910,6 +1910,9 @@ $(objpfx)tst-tls19.out: $(objpfx)tst-tls19mod1.so
>
>  CFLAGS-tst-align.c += $(stack-align-test-flags)
>  CFLAGS-tst-align2.c += $(stack-align-test-flags)
> +ifeq ($(have-test-clang),yes)
> +CFLAGS-tst-align2.c += $(cc-option-wno-implicit-fallthrough)
> +endif
>  CFLAGS-tst-alignmod.c += $(stack-align-test-flags)
>  CFLAGS-tst-alignmod2.c += $(stack-align-test-flags)
>  $(objpfx)tst-align.out: $(objpfx)tst-alignmod.so
> diff --git a/misc/Makefile b/misc/Makefile
> index acd247f2e4..205e7a7ad4 100644
> --- a/misc/Makefile
> +++ b/misc/Makefile
> @@ -338,6 +338,9 @@ CFLAGS-getsysstats.c += -fexceptions
>  CFLAGS-getusershell.c += -fexceptions
>  CFLAGS-err.c += -fexceptions
>  CFLAGS-tst-tsearch.c += $(stack-align-test-flags)
> +ifeq ($(have-test-clang),yes)
> +CFLAGS-tst-tsearch.c += $(cc-option-wno-implicit-fallthrough)
> +endif
>  CFLAGS-msync.c += -fexceptions -fasynchronous-unwind-tables
>  CFLAGS-fdatasync.c += -fexceptions -fasynchronous-unwind-tables
>  CFLAGS-fsync.c += -fexceptions -fasynchronous-unwind-tables
> --
> 2.47.1
> ---
>  elf/tst-align2.c   | 4 ++++
>  misc/tst-tsearch.c | 4 ++++
>  2 files changed, 8 insertions(+)
>
> diff --git a/elf/tst-align2.c b/elf/tst-align2.c
> index c73ea5a5fe..c49ed70c17 100644
> --- a/elf/tst-align2.c
> +++ b/elf/tst-align2.c
> @@ -22,6 +22,7 @@
>  #include <sys/wait.h>
>  #include <tst-stack-align.h>
>  #include <unistd.h>
> +#include <libc-diag.h>
>  
>  static int res, fds[2], result;
>  static bool test_destructors;
> @@ -91,6 +92,8 @@ do_test (void)
>    int des_seen = 0, dso_des_seen = 0;
>    while ((len = TEMP_FAILURE_RETRY (read (fds[0], &c, 1))) > 0)
>      {
> +      DIAG_PUSH_NEEDS_COMMENT_CLANG;
> +      DIAG_IGNORE_NEEDS_COMMENT_CLANG (3.2, "-Wimplicit-fallthrough");
>        switch (c)
>          {
>          case 'B':
> @@ -112,6 +115,7 @@ do_test (void)
>            result = 1;
>            break;
>          }
> +      DIAG_POP_NEEDS_COMMENT_CLANG;
>      }
>  
>    close (fds[0]);
> diff --git a/misc/tst-tsearch.c b/misc/tst-tsearch.c
> index 2ca561dd7d..2a8f13f774 100644
> --- a/misc/tst-tsearch.c
> +++ b/misc/tst-tsearch.c
> @@ -26,6 +26,7 @@
>  #include <search.h>
>  #include <tst-stack-align.h>
>  #include <support/check.h>
> +#include <libc-diag.h>
>  
>  #define SEED 0
>  #define BALANCED 1
> @@ -286,6 +287,8 @@ mangle_tree (enum order how, enum action what, void **root, int lag)
>  	  abort ();
>  	}
>  
> +      DIAG_PUSH_NEEDS_COMMENT_CLANG;
> +      DIAG_IGNORE_NEEDS_COMMENT_CLANG (3.2, "-Wimplicit-fallthrough");

Why is this needed with the configure check?

>        switch (what)
>  	{
>  	case build_and_del:
> @@ -331,6 +334,7 @@ mangle_tree (enum order how, enum action what, void **root, int lag)
>  	  break;
>  
>  	}
> +      DIAG_POP_NEEDS_COMMENT_CLANG;
>      }
>  }