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

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