efi: libstub: Use '-std=gnu11' to fix build with GCC 15

commit 8ba14d9f490aef9fd535c04e9e62e1169eb7a055 upstream.

GCC 15 changed the default C standard version to C23, which should not
have impacted the kernel because it requests the gnu11 standard via
'-std=' in the main Makefile. However, the EFI libstub Makefile uses its
own set of KBUILD_CFLAGS for x86 without a '-std=' value (i.e., using
the default), resulting in errors from the kernel's definitions of bool,
true, and false in stddef.h, which are reserved keywords under C23.

  ./include/linux/stddef.h:11:9: error: expected identifier before ‘false’
     11 |         false   = 0,
  ./include/linux/types.h:35:33: error: two or more data types in declaration specifiers
     35 | typedef _Bool                   bool;

Set '-std=gnu11' in the x86 cflags to resolve the error and consistently
use the same C standard version for the entire kernel. All other
architectures reuse KBUILD_CFLAGS from the rest of the kernel, so this
issue is not visible for them.

Cc: stable@vger.kernel.org
Reported-by: Kostadin Shishmanov <kostadinshishmanov@protonmail.com>
Closes: https://lore.kernel.org/4OAhbllK7x4QJGpZjkYjtBYNLd_2whHx9oFiuZcGwtVR4hIzvduultkgfAIRZI3vQpZylu7Gl929HaYFRGeMEalWCpeMzCIIhLxxRhq4U-Y=@protonmail.com/
Reported-by: Jakub Jelinek <jakub@redhat.com>
Closes: https://lore.kernel.org/Z4467umXR2PZ0M1H@tucnak/
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index 433e11dab4a87de086f676e52fc19f2a3cb1a09c..d7bcfe0d50d1fd6d9539ced0427e5ddc2d9fdf20 100644 (file)
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -7,7 +7,7 @@
 #
 cflags-$(CONFIG_X86_32)                := -march=i386
 cflags-$(CONFIG_X86_64)                := -mcmodel=small
-cflags-$(CONFIG_X86)           += -m$(BITS) -D__KERNEL__ \
+cflags-$(CONFIG_X86)           += -m$(BITS) -D__KERNEL__ -std=gnu11 \
                                   -fPIC -fno-strict-aliasing -mno-red-zone \
                                   -mno-mmx -mno-sse -fshort-wchar \
                                   -Wno-pointer-sign \