Two backports linked to build issues with GCC 15 have failed in this version:
- ee2ab467bddf ("x86/boot: Use '-std=gnu11' to fix build with GCC 15") - 8ba14d9f490a ("efi: libstub: Use '-std=gnu11' to fix build with GCC 15")
Conflicts have been solved, and described.
After that, this kernel version still didn't build with GCC 15:
In file included from include/uapi/linux/posix_types.h:5, from include/uapi/linux/types.h:14, from include/linux/types.h:6, from arch/x86/realmode/rm/wakeup.h:11, from arch/x86/realmode/rm/wakemain.c:2: 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:30:33: error: 'bool' cannot be defined via 'typedef' 30 | typedef _Bool bool; | ^~~~ include/linux/types.h:30:33: note: 'bool' is a keyword with '-std=c23' onwards include/linux/types.h:30:1: warning: useless type name in empty declaration 30 | typedef _Bool bool; | ^~~~~~~
I initially fixed this by adding -std=gnu11 in arch/x86/Makefile, then I realised this fix was already done in an upstream commit, created before the GCC 15 release and not mentioning the error I had. This is patch 3.
When I was investigating my error, I noticed other commits were already backported to stable versions. They were all adding -std=gnu11 in different Makefiles. In their commit message, they were mentioning 'gnu11' was picked to use the same as the one from the main Makefile. But this is not the case in this kernel version. Patch 4 fixes that.
Finally, I noticed extra warnings I didn't have in v5.10. Patch 5 fixes that.
Signed-off-by: Matthieu Baerts (NGI0) matttbe@kernel.org --- Alexey Dobriyan (1): x86/boot: Compile boot code with -std=gnu11 too
Matthieu Baerts (NGI0) (1): arch: back to -std=gnu89 in < v5.18
Nathan Chancellor (3): x86/boot: Use '-std=gnu11' to fix build with GCC 15 efi: libstub: Use '-std=gnu11' to fix build with GCC 15 kernel/profile.c: use cpumask_available to check for NULL cpumask
arch/parisc/boot/compressed/Makefile | 2 +- arch/s390/Makefile | 2 +- arch/s390/purgatory/Makefile | 2 +- arch/x86/Makefile | 2 +- arch/x86/boot/compressed/Makefile | 1 + drivers/firmware/efi/libstub/Makefile | 2 +- kernel/profile.c | 6 +++--- 7 files changed, 9 insertions(+), 8 deletions(-) --- base-commit: cda7d335d88aa30485536aee3027540f41bf4f10 change-id: 20251017-v5-4-gcc-15-2d2ccb30432c
Best regards,
From: Nathan Chancellor nathan@kernel.org
commit ee2ab467bddfb2d7f68d996dbab94d7b88f8eaf7 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 x86 compressed boot Makefile uses its own set of KBUILD_CFLAGS 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 compressed boot Makefile to resolve the error and consistently use the same C standard version for the entire kernel.
Closes: https://lore.kernel.org/4OAhbllK7x4QJGpZjkYjtBYNLd_2whHx9oFiuZcGwtVR4hIzvduu... Closes: https://lore.kernel.org/Z4467umXR2PZ0M1H@tucnak/ Reported-by: Kostadin Shishmanov kostadinshishmanov@protonmail.com Reported-by: Jakub Jelinek jakub@redhat.com Signed-off-by: Nathan Chancellor nathan@kernel.org Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Reviewed-by: Ard Biesheuvel ardb@kernel.org Cc:stable@vger.kernel.org Link: https://lore.kernel.org/all/20250121-x86-use-std-consistently-gcc-15-v1-1-8a... [ Conflict in the context, because a few commits are not in this version, e.g. commit 527afc212231 ("x86/boot: Check that there are no run-time relocations") and commit 5fe392ff9d1f ("x86/boot/compressed: Move CLANG_FLAGS to beginning of KBUILD_CFLAGS"). The same line can still be added at the same place. ] Signed-off-by: Matthieu Baerts (NGI0) matttbe@kernel.org --- arch/x86/boot/compressed/Makefile | 1 + 1 file changed, 1 insertion(+)
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 62ef24bb2313..e436819859d9 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -27,6 +27,7 @@ targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \ vmlinux.bin.xz vmlinux.bin.lzo vmlinux.bin.lz4
KBUILD_CFLAGS := -m$(BITS) -O2 +KBUILD_CFLAGS += -std=gnu11 KBUILD_CFLAGS += -fno-strict-aliasing $(call cc-option, -fPIE, -fPIC) KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING cflags-$(CONFIG_X86_32) := -march=i386
From: Nathan Chancellor nathan@kernel.org
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_2whHx9oFiuZcGwtVR4hIzvduu... 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 [ Conflict in the context, because commit bbf8e8b0fe04 ("efi/libstub: Optimize for size instead of speed") is not in this version. '-std=gnu11' can still be added at the same place. ] Signed-off-by: Matthieu Baerts (NGI0) matttbe@kernel.org --- drivers/firmware/efi/libstub/Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile index 8c5b5529dbc0..0dc80564bbd2 100644 --- 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__ -O2 \ +cflags-$(CONFIG_X86) += -m$(BITS) -D__KERNEL__ -O2 -std=gnu11 \ -fPIC -fno-strict-aliasing -mno-red-zone \ -mno-mmx -mno-sse -fshort-wchar \ -Wno-pointer-sign \
From: Alexey Dobriyan adobriyan@gmail.com
commit b3bee1e7c3f2b1b77182302c7b2131c804175870 upstream.
Use -std=gnu11 for consistency with main kernel code.
It doesn't seem to change anything in vmlinux.
Signed-off-by: Alexey Dobriyan adobriyan@gmail.com Signed-off-by: Ingo Molnar mingo@kernel.org Acked-by: H. Peter Anvin (Intel) hpa@zytor.com Link: https://lore.kernel.org/r/2058761e-12a4-4b2f-9690-3c3c1c9902a5@p183 [ This kernel version doesn't build with GCC 15:
In file included from include/uapi/linux/posix_types.h:5, from include/uapi/linux/types.h:14, from include/linux/types.h:6, from arch/x86/realmode/rm/wakeup.h:11, from arch/x86/realmode/rm/wakemain.c:2: 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:30:33: error: 'bool' cannot be defined via 'typedef' 30 | typedef _Bool bool; | ^~~~ include/linux/types.h:30:33: note: 'bool' is a keyword with '-std=c23' onwards include/linux/types.h:30:1: warning: useless type name in empty declaration 30 | typedef _Bool bool; | ^~~~~~~
The fix is similar to commit ee2ab467bddf ("x86/boot: Use '-std=gnu11' to fix build with GCC 15") which has been backported to this kernel.
Note: In < 5.18 version, -std=gnu89 is used instead of -std=gnu11, see commit e8c07082a810 ("Kbuild: move to -std=gnu11"). I suggest not to modify that in this commit here as all the other similar fixes to support GCC 15 set -std=gnu11. This can be done in a dedicated commit if needed. There was a conflict, because commit 2838307b019d ("x86/build: Remove -m16 workaround for unsupported versions of GCC") and commit accb8cfd506d ("x86/realmode: build with -D__DISABLE_EXPORTS") are not in this version and change code in the context. -std=gnu11 can still be added at the same place. ] Signed-off-by: Matthieu Baerts (NGI0) matttbe@kernel.org --- Cc: Nathan Chancellor nathan@kernel.org Cc: Dave Hansen dave.hansen@linux.intel.com Cc: Ard Biesheuvel ardb@kernel.org --- arch/x86/Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 69f0cb01c666..69930ed5574b 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -31,7 +31,7 @@ endif CODE16GCC_CFLAGS := -m32 -Wa,$(srctree)/arch/x86/boot/code16gcc.h M16_CFLAGS := $(call cc-option, -m16, $(CODE16GCC_CFLAGS))
-REALMODE_CFLAGS := $(M16_CFLAGS) -g -Os -DDISABLE_BRANCH_PROFILING \ +REALMODE_CFLAGS := -std=gnu11 $(M16_CFLAGS) -g -Os -DDISABLE_BRANCH_PROFILING \ -Wall -Wstrict-prototypes -march=i386 -mregparm=3 \ -fno-strict-aliasing -fomit-frame-pointer -fno-pic \ -mno-mmx -mno-sse $(call cc-option,-fcf-protection=none)
Recent fixes have been backported to < v5.18 to fix build issues with GCC 5.15. They all force -std=gnu11 in the CFLAGS, "because [the kernel] requests the gnu11 standard via '-std=' in the main Makefile".
This is true for >= 5.18 versions, but not before. This switch to -std=gnu11 has been done in commit e8c07082a810 ("Kbuild: move to -std=gnu11").
For a question of uniformity, force -std=gnu89, similar to what is done in the main Makefile.
Note: the fixes tags below refers to upstream commits, but this fix is only for kernels not having commit e8c07082a810 ("Kbuild: move to -std=gnu11").
Fixes: 7cbb015e2d3d ("parisc: fix building with gcc-15") Fixes: 3b8b80e99376 ("s390: Add '-std=gnu11' to decompressor and purgatory CFLAGS") Fixes: b3bee1e7c3f2 ("x86/boot: Compile boot code with -std=gnu11 too") Fixes: ee2ab467bddf ("x86/boot: Use '-std=gnu11' to fix build with GCC 15") Fixes: 8ba14d9f490a ("efi: libstub: Use '-std=gnu11' to fix build with GCC 15") Signed-off-by: Matthieu Baerts (NGI0) matttbe@kernel.org --- Note: An alternative is to backport commit e8c07082a810 ("Kbuild: move to -std=gnu11"), but I guess we might not want to do that for stable, as it might introduce new warnings.
Cc: Nathan Chancellor nathan@kernel.org Cc: Ard Biesheuvel ardb@kernel.org Cc: Alexey Dobriyan adobriyan@gmail.com Cc: Arnd Bergmann arnd@arndb.de --- arch/parisc/boot/compressed/Makefile | 2 +- arch/s390/Makefile | 2 +- arch/s390/purgatory/Makefile | 2 +- arch/x86/Makefile | 2 +- arch/x86/boot/compressed/Makefile | 2 +- drivers/firmware/efi/libstub/Makefile | 2 +- 6 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/arch/parisc/boot/compressed/Makefile b/arch/parisc/boot/compressed/Makefile index 98d69488e5c2..92cab904f1ba 100644 --- a/arch/parisc/boot/compressed/Makefile +++ b/arch/parisc/boot/compressed/Makefile @@ -21,7 +21,7 @@ KBUILD_CFLAGS += -fno-PIE -mno-space-regs -mdisable-fpregs -Os ifndef CONFIG_64BIT KBUILD_CFLAGS += -mfast-indirect-calls endif -KBUILD_CFLAGS += -std=gnu11 +KBUILD_CFLAGS += -std=gnu89
OBJECTS += $(obj)/head.o $(obj)/real2.o $(obj)/firmware.o $(obj)/misc.o $(obj)/piggy.o
diff --git a/arch/s390/Makefile b/arch/s390/Makefile index 22dc393b5a83..287b853a7f09 100644 --- a/arch/s390/Makefile +++ b/arch/s390/Makefile @@ -23,7 +23,7 @@ endif aflags_dwarf := -Wa,-gdwarf-2 KBUILD_AFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -D__ASSEMBLY__ KBUILD_AFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO),$(aflags_dwarf)) -KBUILD_CFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -O2 -std=gnu11 +KBUILD_CFLAGS_DECOMPRESSOR := $(CLANG_FLAGS) -m64 -O2 -std=gnu89 KBUILD_CFLAGS_DECOMPRESSOR += -DDISABLE_BRANCH_PROFILING -D__NO_FORTIFY KBUILD_CFLAGS_DECOMPRESSOR += -fno-delete-null-pointer-checks -msoft-float KBUILD_CFLAGS_DECOMPRESSOR += -fno-asynchronous-unwind-tables diff --git a/arch/s390/purgatory/Makefile b/arch/s390/purgatory/Makefile index 2f4d8422bdfb..facd0b3db637 100644 --- a/arch/s390/purgatory/Makefile +++ b/arch/s390/purgatory/Makefile @@ -20,7 +20,7 @@ GCOV_PROFILE := n UBSAN_SANITIZE := n KASAN_SANITIZE := n
-KBUILD_CFLAGS := -std=gnu11 -fno-strict-aliasing -Wall -Wstrict-prototypes +KBUILD_CFLAGS := -std=gnu89 -fno-strict-aliasing -Wall -Wstrict-prototypes KBUILD_CFLAGS += -Wno-pointer-sign -Wno-sign-compare KBUILD_CFLAGS += -fno-zero-initialized-in-bss -fno-builtin -ffreestanding KBUILD_CFLAGS += -c -MD -Os -m64 -msoft-float -fno-common diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 69930ed5574b..424ee0e1f23d 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -31,7 +31,7 @@ endif CODE16GCC_CFLAGS := -m32 -Wa,$(srctree)/arch/x86/boot/code16gcc.h M16_CFLAGS := $(call cc-option, -m16, $(CODE16GCC_CFLAGS))
-REALMODE_CFLAGS := -std=gnu11 $(M16_CFLAGS) -g -Os -DDISABLE_BRANCH_PROFILING \ +REALMODE_CFLAGS := -std=gnu89 $(M16_CFLAGS) -g -Os -DDISABLE_BRANCH_PROFILING \ -Wall -Wstrict-prototypes -march=i386 -mregparm=3 \ -fno-strict-aliasing -fomit-frame-pointer -fno-pic \ -mno-mmx -mno-sse $(call cc-option,-fcf-protection=none) diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index e436819859d9..5771d5b43bb8 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -27,7 +27,7 @@ targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \ vmlinux.bin.xz vmlinux.bin.lzo vmlinux.bin.lz4
KBUILD_CFLAGS := -m$(BITS) -O2 -KBUILD_CFLAGS += -std=gnu11 +KBUILD_CFLAGS += -std=gnu89 KBUILD_CFLAGS += -fno-strict-aliasing $(call cc-option, -fPIE, -fPIC) KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING cflags-$(CONFIG_X86_32) := -march=i386 diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile index 0dc80564bbd2..00622027a49f 100644 --- 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__ -O2 -std=gnu11 \ +cflags-$(CONFIG_X86) += -m$(BITS) -D__KERNEL__ -O2 -std=gnu89 \ -fPIC -fno-strict-aliasing -mno-red-zone \ -mno-mmx -mno-sse -fshort-wchar \ -Wno-pointer-sign \
From: Nathan Chancellor natechancellor@gmail.com
commit ef70eff9dea66f38f8c2c2dcc7fe4b7a2bbb4921 upstream.
When building with clang + -Wtautological-pointer-compare, these instances pop up:
kernel/profile.c:339:6: warning: comparison of array 'prof_cpu_mask' not equal to a null pointer is always true [-Wtautological-pointer-compare] if (prof_cpu_mask != NULL) ^~~~~~~~~~~~~ ~~~~ kernel/profile.c:376:6: warning: comparison of array 'prof_cpu_mask' not equal to a null pointer is always true [-Wtautological-pointer-compare] if (prof_cpu_mask != NULL) ^~~~~~~~~~~~~ ~~~~ kernel/profile.c:406:26: warning: comparison of array 'prof_cpu_mask' not equal to a null pointer is always true [-Wtautological-pointer-compare] if (!user_mode(regs) && prof_cpu_mask != NULL && ^~~~~~~~~~~~~ ~~~~ 3 warnings generated.
This can be addressed with the cpumask_available helper, introduced in commit f7e30f01a9e2 ("cpumask: Add helper cpumask_available()") to fix warnings like this while keeping the code the same.
Link: https://github.com/ClangBuiltLinux/linux/issues/747 Link: http://lkml.kernel.org/r/20191022191957.9554-1-natechancellor@gmail.com Signed-off-by: Nathan Chancellor natechancellor@gmail.com Reviewed-by: Andrew Morton akpm@linux-foundation.org Cc: Thomas Gleixner tglx@linutronix.de Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org [ These warnings are also visible with recent GCC versions. ] Signed-off-by: Matthieu Baerts (NGI0) matttbe@kernel.org --- kernel/profile.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/profile.c b/kernel/profile.c index b5ce18b6f1b9..af3d5c34d051 100644 --- a/kernel/profile.c +++ b/kernel/profile.c @@ -344,7 +344,7 @@ static int profile_dead_cpu(unsigned int cpu) struct page *page; int i;
- if (prof_cpu_mask != NULL) + if (cpumask_available(prof_cpu_mask)) cpumask_clear_cpu(cpu, prof_cpu_mask);
for (i = 0; i < 2; i++) { @@ -381,7 +381,7 @@ static int profile_prepare_cpu(unsigned int cpu)
static int profile_online_cpu(unsigned int cpu) { - if (prof_cpu_mask != NULL) + if (cpumask_available(prof_cpu_mask)) cpumask_set_cpu(cpu, prof_cpu_mask);
return 0; @@ -411,7 +411,7 @@ void profile_tick(int type) { struct pt_regs *regs = get_irq_regs();
- if (!user_mode(regs) && prof_cpu_mask != NULL && + if (!user_mode(regs) && cpumask_available(prof_cpu_mask) && cpumask_test_cpu(smp_processor_id(), prof_cpu_mask)) profile_hit(type, (void *)profile_pc(regs)); }
linux-stable-mirror@lists.linaro.org
-
Matthieu Baerts (NGI0)