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 as specified in KBUILD_CFLAGS 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@gmail.com>
Cc: stable@vger.kernel.org
---
v2: Filter the -std flag from KBUILD_CFLAGS instead of hardcoding
v3: Adjust subject and commit message

 arch/mips/vdso/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
index fb4c493aaffa..69d4593f64fe 100644
--- a/arch/mips/vdso/Makefile
+++ b/arch/mips/vdso/Makefile
@@ -27,6 +27,7 @@ endif
 # offsets.
 cflags-vdso := $(ccflags-vdso) \
 	$(filter -W%,$(filter-out -Wa$(comma)%,$(KBUILD_CFLAGS))) \
+	$(filter -std=%,$(KBUILD_CFLAGS)) \
 	-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 \

On Sat, Mar 29, 2025 at 08:39:03AM -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 as specified in KBUILD_CFLAGS 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@gmail.com>
> Cc: stable@vger.kernel.org
> ---
> v2: Filter the -std flag from KBUILD_CFLAGS instead of hardcoding
> v3: Adjust subject and commit message
> 
>  arch/mips/vdso/Makefile | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
> index fb4c493aaffa..69d4593f64fe 100644
> --- a/arch/mips/vdso/Makefile
> +++ b/arch/mips/vdso/Makefile
> @@ -27,6 +27,7 @@ endif
>  # offsets.
>  cflags-vdso := $(ccflags-vdso) \
>  	$(filter -W%,$(filter-out -Wa$(comma)%,$(KBUILD_CFLAGS))) \
> +	$(filter -std=%,$(KBUILD_CFLAGS)) \
>  	-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 \

applied to mips-next.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]