Re: [PATCH -next v2 0/2] Remove unused variables in x86/boot

[Li Zetao <lizetao1@huawei.com>]

Hi Nathan,

On 2022/9/28 5:50, Nathan Chancellor wrote:
> Hi Li,
>
> On Tue, Sep 27, 2022 at 08:15:10AM +0000, Li Zetao wrote:
>> This patch set removes some unused variables in x86/boot, and add the
>> "-Wall" flag to Makefile, which is the old problem of x86 not sharing
>> makefiles.
>>
>> Changes since v1:
>> - Add "-Wall" flag to x86/boot/compressed/Makefile
>> - Remove unused variables "et" in efi_get_system_table() and "ret" in
>>    efi_get_conf_table()
>> - Remove unused variables "ret" in __efi_get_rsdp_addr() and
>>    "nr_tables" in efi_get_rsdp_addr()
>>
>> v1 at:
>> https://lore.kernel.org/all/20220923113209.3046960-1-lizetao1@huawei.com/
>>
>> Li Zetao (2):
>>    x86/boot/compressed: Add "-Wall" flag to Makefile
>>    x86/boot: Remove unused variables
>>
>>   arch/x86/boot/compressed/Makefile | 2 +-
>>   arch/x86/boot/compressed/acpi.c   | 2 --
>>   arch/x86/boot/compressed/efi.c    | 2 --
>>   arch/x86/boot/compressed/sev.c    | 1 -
>>   4 files changed, 1 insertion(+), 6 deletions(-)
> I took this series for a spin with clang and found a few extra warnings.
>
> 1.
>
>    In file included from arch/x86/boot/compressed/misc.c:15:
>    In file included from arch/x86/boot/compressed/misc.h:24:
>    In file included from ./include/linux/elf.h:6:
>    In file included from ./arch/x86/include/asm/elf.h:8:
>    In file included from ./include/linux/thread_info.h:60:
>    ./arch/x86/include/asm/thread_info.h:175:13: warning: calling '__builtin_frame_address' with a nonzero argument is unsafe [-Wframe-address]
>            oldframe = __builtin_frame_address(1);
>                       ^~~~~~~~~~~~~~~~~~~~~~~~~~
>    ./arch/x86/include/asm/thread_info.h:177:11: warning: calling '__builtin_frame_address' with a nonzero argument is unsafe [-Wframe-address]
>                    frame = __builtin_frame_address(2);
>                            ^~~~~~~~~~~~~~~~~~~~~~~~~~
>
> This warning is disabled in the main Makefile for this reason so we
> should just be able to disable it:
>
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index 10abb7c45d04..3f004567f3d5 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -43,6 +43,7 @@ KBUILD_CFLAGS += -mno-mmx -mno-sse
>   KBUILD_CFLAGS += -ffreestanding -fshort-wchar
>   KBUILD_CFLAGS += -fno-stack-protector
>   KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
> +KBUILD_CFLAGS += $(call cc-disable-warning, frame-address)
>   KBUILD_CFLAGS += $(call cc-disable-warning, gnu)
>   KBUILD_CFLAGS += -Wno-pointer-sign
>   KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
>
> 2.
>
>    arch/x86/boot/compressed/kaslr.c:627:6: warning: unused variable 'i' [-Wunused-variable]
>            int i;
>                ^
>
> This happens when CONFIG_MEMORY_HOTREMOVE or CONFIG_ACPI are 'n'. I
> think it can just be fixed by aligning arch/x86/boot/compressed with the
> rest of the kernel and explicitly compiling with '-std=gnu11', which
> will allow us to declare the variable within the for loop, like so.
>
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index 3f004567f3d5..6c7e366a437b 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -34,7 +34,7 @@ targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \
>   # be valid.
>   KBUILD_CFLAGS := -m$(BITS) -O2 $(CLANG_FLAGS)
>   KBUILD_CFLAGS += -fno-strict-aliasing -fPIE
> -KBUILD_CFLAGS += -Wundef -Wall
> +KBUILD_CFLAGS += -Wundef -Wall -std=gnu11
>   KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
>   cflags-$(CONFIG_X86_32) := -march=i386
>   cflags-$(CONFIG_X86_64) := -mcmodel=small -mno-red-zone
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index 4a3f223973f4..be859c7e7f6b 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -624,7 +624,6 @@ static bool process_mem_region(struct mem_vector *region,
>   			       unsigned long minimum,
>   			       unsigned long image_size)
>   {
> -	int i;
>   	/*
>   	 * If no immovable memory found, or MEMORY_HOTREMOVE disabled,
>   	 * use @region directly.
> @@ -644,7 +643,7 @@ static bool process_mem_region(struct mem_vector *region,
>   	 * If immovable memory found, filter the intersection between
>   	 * immovable memory and @region.
>   	 */
> -	for (i = 0; i < num_immovable_mem; i++) {
> +	for (int i = 0; i < num_immovable_mem; i++) {
>   		u64 start, end, entry_end, region_end;
>   		struct mem_vector entry;
>   
>
> Additionally, I think these two patches should be reordered so that the
> warnings are fixed before they are enabled.
>
> With those comments addressed, consider the series:
>
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>
>
> Cheers,
> Nathan

What is your clang compiler version and .config? My clang compiler is 
14.0.0-1ubuntu1, and I can't reproduce

problem 1("calling '__builtin_frame_address' with a nonzero argument is 
unsafe"). Can you provide more

information.


Thx.


Best regards,

Li Zetao