linux-kernel - Re: [PATCH] mips: Add '-std=gnu11' to vdso CFLAGS

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Message-ID: <Z98q-CurZoru9Qr3@fjasle.eu>
Date: Sat, 22 Mar 2025 22:26:16 +0100
From: Nicolas Schier <nicolas@...sle.eu>
To: Khem Raj <raj.khem@...il.com>
Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
 Masahiro Yamada <masahiroy@...nel.org>, Kees Cook <kees@...nel.org>,
 linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
 stable@...r.kernel.org
Subject: Re: [PATCH] mips: Add '-std=gnu11' to vdso CFLAGS

On Fri, Mar 21, 2025 at 05:09:40PM -0700 Khem Raj wrote:
> GCC 15 changed the default C standard dialect from gnu17 to gnu23,
> which should not have impacted the kernel because it explicitly requests
> the gnu11 standard in the main Makefile. However, mips/vdso code uses
> its own CFLAGS without a '-std=' value, which break with this dialect
> change because of the kernel's own definitions of bool, false, and true
> conflicting with the C23 reserved keywords.
> 
>   include/linux/stddef.h:11:9: error: cannot use keyword 'false' as enumeration constant
>      11 |         false   = 0,
>         |         ^~~~~
>   include/linux/stddef.h:11:9: note: 'false' is a keyword with '-std=c23' onwards
>   include/linux/types.h:35:33: error: 'bool' cannot be defined via 'typedef'
>      35 | typedef _Bool                   bool;
>         |                                 ^~~~
>   include/linux/types.h:35:33: note: 'bool' is a keyword with '-std=c23' onwards
> 
> Add '-std=gnu11' to the decompressor and purgatory CFLAGS to eliminate
> these errors and make the C standard version of these areas match the
> rest of the kernel.
> 
> Signed-off-by: Khem Raj <raj.khem@...il.com>
> Cc: stable@...r.kernel.org
> ---
>  arch/mips/vdso/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
> index b289b2c1b294..15521004c563 100644
> --- a/arch/mips/vdso/Makefile
> +++ b/arch/mips/vdso/Makefile
> @@ -30,7 +30,7 @@ cflags-vdso := $(ccflags-vdso) \
>  	-O3 -g -fPIC -fno-strict-aliasing -fno-common -fno-builtin -G 0 \
>  	-mrelax-pic-calls $(call cc-option, -mexplicit-relocs) \
>  	-fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \
> -	$(call cc-option, -fno-asynchronous-unwind-tables)
> +	$(call cc-option, -fno-asynchronous-unwind-tables) -std=gnu11
>  aflags-vdso := $(ccflags-vdso) \
>  	-D__ASSEMBLY__ -Wa,-gdwarf-2
>  

Thanks for the patch.  Did you evaluate adding a line like

    $(filter -std=%,$(KBUILD_CFLAGS)) \

to the assignment of ccflags-vdso?  Then MIPS VDSO C standard keeps aligned
with top-level.

Nevertheless,
Reviewed-by: Nicolas Schier <nicolas@...sle.eu>