Re: [PATCH -next v4 2/2] x86/boot/compressed: Add "-Wall" flag to Makefile

From: Nick Desaulniers <ndesaulniers@google.com>
To: Li Zetao <lizetao1@huawei.com>
Cc: keescook@chromium.org, tglx@linutronix.de, mingo@redhat.com,
	bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org,
	hpa@zytor.com, kirill.shutemov@linux.intel.com,
	tony.luck@intel.com, masahiroy@kernel.org, michael.roth@amd.com,
	sathyanarayanan.kuppuswamy@linux.intel.com, nathan@kernel.org,
	brijesh.singh@amd.com, peterz@infradead.org,
	venu.busireddy@oracle.com, linux-kernel@vger.kernel.org,
	akpm@linux-foundation.org
Subject: Re: [PATCH -next v4 2/2] x86/boot/compressed: Add "-Wall" flag to Makefile
Date: Tue, 11 Oct 2022 14:20:36 -0700	[thread overview]
Message-ID: <CAKwvOdmK6Niv3x-K0__5fqJ+N27wiQaB0v7kS-iAAJfBXGk7XA@mail.gmail.com> (raw)
In-Reply-To: <20221011012904.2330473-3-lizetao1@huawei.com>

On Mon, Oct 10, 2022 at 6:32 PM Li Zetao <lizetao1@huawei.com> wrote:
>
> Compressed/Makefile does not have "-Wall" flag, this is the old problem of
> x86 not sharing makefiles. Fix by adding "-Wall" flag to Makefile. But when
> "-Wall" flag added to Makefile, a few extra warnings were found.
>
> 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, adding "frame-address" flag to
> Makefile.
>
> 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".
> Fix by adding "-std=gnu11" flag to Makefile, and we should put
> the variable "i" within the for loop.
>
> 3.
> arch/x86/boot/compressed/acpi.c:23:1: warning: unused function
>   "__efi_get_rsdp_addr" [-Wunused-function]
>
> This happens when CONFIG_EFI is disabled for the reason that
> function "__efi_get_rsdp_addr" is only called in efi_get_rsdp_addr
> when CONFIG_EFI enable. So function "__efi_get_rsdp_addr" should
> not be defined when CONFIG_EFI is disabled.
>
> Signed-off-by: Li Zetao <lizetao1@huawei.com>

I gave this a quick spin with clang to ensure that I didn't observe
new warnings produced via -Wall:

$ make LLVM=1 -j128 -s defconfig all
$ make LLVM=1 ARCH=i386 -j128 -s defconfig all

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
> v1 -> v2: Patch is new
> v2 -> v3: Resolve extra warnings after "-Wall" flag added
> v3 -> v4: Put this patch at the end
>
>  arch/x86/boot/compressed/Makefile | 3 ++-
>  arch/x86/boot/compressed/acpi.c   | 5 +++--
>  arch/x86/boot/compressed/kaslr.c  | 3 +--
>  3 files changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index 3a261abb6d15..8918a8306dff 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -35,7 +35,7 @@ targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \
>  # be valid.
>  KBUILD_CFLAGS := -m$(BITS) -O2 $(CLANG_FLAGS)
>  KBUILD_CFLAGS += -fno-strict-aliasing -fPIE
> -KBUILD_CFLAGS += -Wundef
> +KBUILD_CFLAGS += -Wundef -Wall -std=gnu11
>  KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
>  cflags-$(CONFIG_X86_32) := -march=i386
>  cflags-$(CONFIG_X86_64) := -mcmodel=small -mno-red-zone
> @@ -44,6 +44,7 @@ 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)/=)
> diff --git a/arch/x86/boot/compressed/acpi.c b/arch/x86/boot/compressed/acpi.c
> index 21febd9f21ab..c062a8230e9c 100644
> --- a/arch/x86/boot/compressed/acpi.c
> +++ b/arch/x86/boot/compressed/acpi.c
> @@ -19,10 +19,10 @@
>   */
>  struct mem_vector immovable_mem[MAX_NUMNODES*2];
>
> +#ifdef CONFIG_EFI
>  static acpi_physical_address
>  __efi_get_rsdp_addr(unsigned long cfg_tbl_pa, unsigned int cfg_tbl_len)
>  {
> -#ifdef CONFIG_EFI
>         unsigned long rsdp_addr;
>
>         /*
> @@ -41,9 +41,10 @@ __efi_get_rsdp_addr(unsigned long cfg_tbl_pa, unsigned int cfg_tbl_len)
>                 return (acpi_physical_address)rsdp_addr;
>
>         debug_putstr("Error getting RSDP address.\n");
> -#endif
> +
>         return 0;
>  }
> +#endif
>
>  static acpi_physical_address efi_get_rsdp_addr(void)
>  {
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index e476bcbd9b42..4abc9c42cf4d 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -625,7 +625,6 @@ 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.
> @@ -645,7 +644,7 @@ 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;
>
> --
> 2.34.1
>

-- 
Thanks,
~Nick Desaulniers