linux-kernel - Re: [PATCH-next v3] arm32: enable HAVE_LD_DEAD_CODE_DATA

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Date: Fri, 15 Mar 2024 20:10:05 +0800
From: "liuyuntao (F)" <liuyuntao12@...wei.com>
To: Arnd Bergmann <arnd@...db.de>, Ard Biesheuvel <ardb@...nel.org>
CC: <linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>, Russell King
	<linux@...linux.org.uk>, Andrew Davis <afd@...com>, Andrew Morton
	<akpm@...ux-foundation.org>, "Kirill A. Shutemov"
	<kirill.shutemov@...ux.intel.com>, Geert Uytterhoeven
	<geert+renesas@...der.be>, Jonathan Corbet <corbet@....net>, Mike Rapoport
	<rppt@...nel.org>, Rob Herring <robh@...nel.org>, Thomas Gleixner
	<tglx@...utronix.de>, Linus Walleij <linus.walleij@...aro.org>, Fangrui Song
	<maskray@...gle.com>
Subject: Re: [PATCH-next v3] arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION



On 2024/3/15 19:51, Arnd Bergmann wrote:
> On Fri, Mar 15, 2024, at 12:48, liuyuntao (F) wrote:
>> On 2024/3/15 18:46, Ard Biesheuvel wrote:
>>> @@ -28,6 +28,7 @@
>>>                                      -DEFI_HAVE_MEMCHR -DEFI_HAVE_STRRCHR \
>>>                                      -DEFI_HAVE_STRCMP -fno-builtin -fpic \
>>>                                      $(call cc-option,-mno-single-pic-base)
>>> +cflags-$(CONFIG_ARM)           := $(filter-out -fdata-sections, $(CFLAGS-y))
>>>    cflags-$(CONFIG_RISCV)         += -fpic -DNO_ALTERNATIVE -mno-relax
>>>    cflags-$(CONFIG_LOONGARCH)     += -fpie
>>
>> Another error:
>> cannot initialize array of ‘short unsigned int’ from a string literal
>> with type array of ‘unsigned int’
>>    17 | static const efi_char16_t shim_MokSBState_name[] = L"MokSBStateRT";
> 
> The line sets cflags-y to an empty string.
> 
> It probably should have been
> 
> cflags-$(CONFIG_ARM)           := $(filter-out -fdata-sections, $(cflags-y))
> 
> (small cflags instead of CFLAGS).
> 
>       Arnd

Oh, my mistake, after fixed this bug, still this error:
> arm-linux-gnueabi-ld: warning: orphan section `.data.efi_loglevel' from `drivers/firmware/efi/libstub/printk.stub.o' being placed in section `.data.efi_loglevel'
> arm-linux-gnueabi-ld: warning: orphan section `.data.screen_info_guid' from `drivers/firmware/efi/libstub/screen_info.stub.o' being placed in section `.data.screen_info_guid'
> arm-linux-gnueabi-ld: warning: orphan section `.data.cpu_state_guid' from `drivers/firmware/efi/libstub/arm32-stub.stub.o' being placed in section `.data.cpu_state_guid'
> arm-linux-gnueabi-ld: warning: orphan section `.data.efi_nokaslr' from `drivers/firmware/efi/libstub/efi-stub-helper.stub.o' being placed in section `.data.efi_nokaslr'

The -fdata-sections option is present in the KBUILD_CFLAGS_KERNEL 
variable; altering cflags-y only affect the KBUILD_CFLAGS variable.
It seems that the -fdata-sections option needs to be removed from the 
KBUILD_CFLAGS_KERNEL variable.
> ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
> KBUILD_CFLAGS_KERNEL += -ffunction-sections -fdata-sections
> KBUILD_RUSTFLAGS_KERNEL += -Zfunction-sections=y
> LDFLAGS_vmlinux += --gc-sections
> endif