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

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Message-ID: <CAMj1kXEkd-MAN8x88DPTnkZzojg8TRbTgzujO+DZCpo58mZxaA@mail.gmail.com>
Date: Fri, 15 Mar 2024 13:58:14 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: "liuyuntao (F)" <liuyuntao12@...wei.com>
Cc: Arnd Bergmann <arnd@...db.de>, 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 Fri, 15 Mar 2024 at 13:52, liuyuntao (F) <liuyuntao12@...wei.com> wrote:
>
>
>
> On 2024/3/15 20:46, Ard Biesheuvel wrote:
> > On Fri, 15 Mar 2024 at 13:22, liuyuntao (F) <liuyuntao12@...wei.com> wrote:
> >>
> >>
> >>
> >> On 2024/3/15 20:13, Ard Biesheuvel wrote:
> >>> On Fri, 15 Mar 2024 at 13:10, liuyuntao (F) <liuyuntao12@...wei.com> wrote:
> >>>>
> >>>>
> >>>>
> >>>> 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).
> >>>>>
> >>>
> >>> Oops indeed.
> >>>
> >>>> 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.
> >>>
> >>> Indeed.
> >>>
> >>> So
> >>>
> >>> KBUILD_CFLAGS_KERNEL := $(filter-out -fdata-sections,$(KBUILD_CFLAGS_KERNEL))
> >>>
> >>> (assuming I got it right this time without build testing)
> >>
> >> Um, it not worked,too, same error.
> >
> > Aren't you missing a 'L' ?
> >
> >>> --- a/drivers/firmware/efi/libstub/Makefile
> >>> +++ b/drivers/firmware/efi/libstub/Makefile
> >>> @@ -28,6 +28,7 @@ cflags-$(CONFIG_ARM)          += -DEFI_HAVE_STRLEN -DEFI_HAVE_STRNLEN \
> >>>                                     -DEFI_HAVE_MEMCHR -DEFI_HAVE_STRRCHR \
> >>>
> >
> >>> 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
> >>
> >>                                    -DEFI_HAVE_STRCMP -fno-builtin -fpic \
> >>>                                     $(call cc-option,-mno-single-pic-base)
> >>> +KBUILD_CFLAGS_KERNE            := $(filter-out -fdata-sections, $(KBUILD_CFLAGS_KERNE))
> >>>   cflags-$(CONFIG_RISCV)         += -fpic -DNO_ALTERNATIVE -mno-relax
> >>>   cflags-$(CONFIG_LOONGARCH)     += -fpie
> >>
> >>
> Sorry, I was too careless.
> How about reset KBUILD_CFLAGS_KERNEL?
>

No, that is not the solution.

Either avoid setting -fdata-sections altogether, or filter it out.


> > +# KBUILD_CFLAGS_KERNEL is is set by CONFIG_LD_DEAD_CODE_DATA_ELIMINATION,
> > +# not need here, just reset it.
> > +KBUILD_CFLAGS_KERNEL :=
> > +
> >  # non-x86 reuses KBUILD_CFLAGS, x86 does not
> >  cflags-y                       := $(KBUILD_CFLAGS)
>