[PATCH 0/2] tools/nolibc: avoid -Wundef warnings

[PATCH 0/2] tools/nolibc: avoid -Wundef warnings

[Thomas Weißschuh]

Make sure nolibc does not trigger -Wundef warnings.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
Thomas Weißschuh (2):
      tools/nolibc: avoid -Wundef warning for __STDC_VERSION__
      selftests/nolibc: enable -Wundef

 tools/include/nolibc/compiler.h                 | 8 +++++++-
 tools/testing/selftests/nolibc/Makefile.include | 3 ++-
 2 files changed, 9 insertions(+), 2 deletions(-)
---
base-commit: d59131de97ee69ab4e4b8926089a6e953d699b11
change-id: 20260318-nolibc-wundef-fee232c29559

Best regards,
-- 
Thomas Weißschuh <linux@weissschuh.net>

[PATCH 1/2] tools/nolibc: avoid -Wundef warning for __STDC_VERSION__

[Thomas Weißschuh]

With -std=c89 the macro __STDC_VERSION__ is not defined.
While undefined identifiers in '#if' directives are assumed to be '0',
with -Wundef a warning is emitted.

Avoid the warning by explicitly falling back to '0' if __STDC_VERSION__
is not provided by the preprocessor.

Fixes: 37219aa5b123 ("tools/nolibc: add __nolibc_static_assert()")
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 tools/include/nolibc/compiler.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/tools/include/nolibc/compiler.h b/tools/include/nolibc/compiler.h
index f03f84cfadce..dac09badff0a 100644
--- a/tools/include/nolibc/compiler.h
+++ b/tools/include/nolibc/compiler.h
@@ -47,6 +47,12 @@
 #  define __nolibc_fallthrough do { } while (0)
 #endif /* __nolibc_has_attribute(fallthrough) */
 
+#ifdef __STDC_VERSION__
+#  define __nolibc_stdc_version __STDC_VERSION__
+#else
+#  define __nolibc_stdc_version 0
+#endif
+
 #define __nolibc_version(_major, _minor, _patch) ((_major) * 10000 + (_minor) * 100 + (_patch))
 
 #ifdef __GNUC__
@@ -63,7 +69,7 @@
 #  define __nolibc_clang_version 0
 #endif /* __clang__ */
 
-#if __STDC_VERSION__ >= 201112L || \
+#if __nolibc_stdc_version >= 201112L || \
 	__nolibc_gnuc_version >= __nolibc_version(4, 6, 0) || \
 	__nolibc_clang_version >= __nolibc_version(3, 0, 0)
 #  define __nolibc_static_assert(_t) _Static_assert(_t, "")

-- 
2.53.0

Re: [PATCH 1/2] tools/nolibc: avoid -Wundef warning for __STDC_VERSION__

[David Laight]

On Wed, 18 Mar 2026 17:12:42 +0100
Thomas Weißschuh <linux@weissschuh.net> wrote:

> With -std=c89 the macro __STDC_VERSION__ is not defined.
> While undefined identifiers in '#if' directives are assumed to be '0',
> with -Wundef a warning is emitted.
> 
> Avoid the warning by explicitly falling back to '0' if __STDC_VERSION__
> is not provided by the preprocessor.
> 
> Fixes: 37219aa5b123 ("tools/nolibc: add __nolibc_static_assert()")
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> ---
>  tools/include/nolibc/compiler.h | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/include/nolibc/compiler.h b/tools/include/nolibc/compiler.h
> index f03f84cfadce..dac09badff0a 100644
> --- a/tools/include/nolibc/compiler.h
> +++ b/tools/include/nolibc/compiler.h
> @@ -47,6 +47,12 @@
>  #  define __nolibc_fallthrough do { } while (0)
>  #endif /* __nolibc_has_attribute(fallthrough) */
>  
> +#ifdef __STDC_VERSION__
> +#  define __nolibc_stdc_version __STDC_VERSION__
> +#else
> +#  define __nolibc_stdc_version 0
> +#endif

How about:
#ifndef __STDC_VERSION__
#define __STDC_VERSION__ 198900
#endif

	David

> +
>  #define __nolibc_version(_major, _minor, _patch) ((_major) * 10000 + (_minor) * 100 + (_patch))
>  
>  #ifdef __GNUC__
> @@ -63,7 +69,7 @@
>  #  define __nolibc_clang_version 0
>  #endif /* __clang__ */
>  
> -#if __STDC_VERSION__ >= 201112L || \
> +#if __nolibc_stdc_version >= 201112L || \
>  	__nolibc_gnuc_version >= __nolibc_version(4, 6, 0) || \
>  	__nolibc_clang_version >= __nolibc_version(3, 0, 0)
>  #  define __nolibc_static_assert(_t) _Static_assert(_t, "")
> 

Re: [PATCH 1/2] tools/nolibc: avoid -Wundef warning for __STDC_VERSION__

[Thomas Weißschuh]

On 2026-03-19 10:24:14+0000, David Laight wrote:
> On Wed, 18 Mar 2026 17:12:42 +0100
> Thomas Weißschuh <linux@weissschuh.net> wrote:
> 
> > With -std=c89 the macro __STDC_VERSION__ is not defined.
> > While undefined identifiers in '#if' directives are assumed to be '0',
> > with -Wundef a warning is emitted.
> > 
> > Avoid the warning by explicitly falling back to '0' if __STDC_VERSION__
> > is not provided by the preprocessor.
> > 
> > Fixes: 37219aa5b123 ("tools/nolibc: add __nolibc_static_assert()")
> > Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> > ---
> >  tools/include/nolibc/compiler.h | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/tools/include/nolibc/compiler.h b/tools/include/nolibc/compiler.h
> > index f03f84cfadce..dac09badff0a 100644
> > --- a/tools/include/nolibc/compiler.h
> > +++ b/tools/include/nolibc/compiler.h
> > @@ -47,6 +47,12 @@
> >  #  define __nolibc_fallthrough do { } while (0)
> >  #endif /* __nolibc_has_attribute(fallthrough) */
> >  
> > +#ifdef __STDC_VERSION__
> > +#  define __nolibc_stdc_version __STDC_VERSION__
> > +#else
> > +#  define __nolibc_stdc_version 0
> > +#endif
> 
> How about:
> #ifndef __STDC_VERSION__
> #define __STDC_VERSION__ 198900
> #endif

That may break applications, so I'd rather not do it.

> > +
> >  #define __nolibc_version(_major, _minor, _patch) ((_major) * 10000 + (_minor) * 100 + (_patch))
> >  
> >  #ifdef __GNUC__
> > @@ -63,7 +69,7 @@
> >  #  define __nolibc_clang_version 0
> >  #endif /* __clang__ */
> >  
> > -#if __STDC_VERSION__ >= 201112L || \
> > +#if __nolibc_stdc_version >= 201112L || \
> >  	__nolibc_gnuc_version >= __nolibc_version(4, 6, 0) || \
> >  	__nolibc_clang_version >= __nolibc_version(3, 0, 0)
> >  #  define __nolibc_static_assert(_t) _Static_assert(_t, "")
> > 
> 

[PATCH 2/2] selftests/nolibc: enable -Wundef

[Thomas Weißschuh]

Users might use -Wundef, so also use it in the nolibc testsuite to
ensure no warnings are triggered.

The existing line with warning options is getting too long,
so move all warnings to a dedicated line.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 tools/testing/selftests/nolibc/Makefile.include | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/nolibc/Makefile.include b/tools/testing/selftests/nolibc/Makefile.include
index 41a0039f774c..96fe2bc2191e 100644
--- a/tools/testing/selftests/nolibc/Makefile.include
+++ b/tools/testing/selftests/nolibc/Makefile.include
@@ -5,7 +5,8 @@ _CFLAGS_STACKPROTECTOR ?= $(call try-run, \
 	echo 'void foo(void) {}' | $(CC) -x c - -o - -S $(CLANG_CROSS_FLAGS) $(__CFLAGS_STACKPROTECTOR) | grep -q __stack_chk_guard, \
 	$(__CFLAGS_STACKPROTECTOR))
 _CFLAGS_SANITIZER ?= $(call cc-option,-fsanitize=undefined -fsanitize-trap=all)
-CFLAGS_NOLIBC_TEST  ?= -Os -fno-ident -fno-asynchronous-unwind-tables -std=c89 -W -Wall -Wextra \
+CFLAGS_NOLIBC_TEST  ?= -Os -fno-ident -fno-asynchronous-unwind-tables -std=c89 \
+		-W -Wall -Wextra -Wundef \
 		$(call cc-option,-fno-stack-protector) $(call cc-option,-Wmissing-prototypes) \
 		$(_CFLAGS_STACKPROTECTOR) $(_CFLAGS_SANITIZER)
 

-- 
2.53.0

Re: [PATCH 0/2] tools/nolibc: avoid -Wundef warnings

[Willy Tarreau]

On Wed, Mar 18, 2026 at 05:12:41PM +0100, Thomas Weißschuh wrote:
> Make sure nolibc does not trigger -Wundef warnings.
> 
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>

Yeah I think it's fairly reasonable like this. For the whole series:

Acked-by: Willy Tarreau <w@1wt.eu>

Thanks!
Willy