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Date:   Mon, 20 Nov 2023 09:33:19 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     WANG Xuerui <kernel@...0n.name>, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
        Ard Biesheuvel <ardb@...nel.org>,
        Simon Glass <sjg@...omium.org>
Subject: Re: [PATCH] loongarch: add dependency between vmlinuz.efi and vmlinux.efi

Hi, Masahiro,

On Sun, Nov 19, 2023 at 10:25 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> On Sun, Nov 19, 2023 at 8:59 PM Huacai Chen <chenhuacai@...nel.org> wrote:
> >
> > Hi, Masahiro,
> >
> > On Sun, Nov 19, 2023 at 1:35 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
> > >
> > > A common issue in Makefile is a race in parallel building.
> > >
> > > You need to be careful to prevent multiple threads from writing to the
> > > same file simultaneously.
> > >
> > > Commit 3939f3345050 ("ARM: 8418/1: add boot image dependencies to not
> > > generate invalid images") addressed such a bad scenario.
> > >
> > > A similar symptom occurs with the following command:
> > >
> > >   $ make -j$(nproc) ARCH=loongarch vmlinux.efi vmlinuz.efi
> > >     [ snip ]
> > >     SORTTAB vmlinux
> > >     OBJCOPY arch/loongarch/boot/vmlinux.efi
> > >     OBJCOPY arch/loongarch/boot/vmlinux.efi
> > >     PAD     arch/loongarch/boot/vmlinux.bin
> > >     GZIP    arch/loongarch/boot/vmlinuz
> > >     OBJCOPY arch/loongarch/boot/vmlinuz.o
> > >     LD      arch/loongarch/boot/vmlinuz.efi.elf
> > >     OBJCOPY arch/loongarch/boot/vmlinuz.efi
> > >
> > > The log "OBJCOPY arch/loongarch/boot/vmlinux.efi" is displayed twice.
> > >
> > > It indicates that two threads simultaneously enter arch/loongarch/boot/
> > > and write to arch/loongarch/boot/vmlinux.efi.
> > >
> > > It occasionally leads to a build failure:
> > >
> > >   $ make -j$(nproc) ARCH=loongarch vmlinux.efi vmlinuz.efi
> > >     [ snip ]
> > >     SORTTAB vmlinux
> > >     OBJCOPY arch/loongarch/boot/vmlinux.efi
> > >     PAD     arch/loongarch/boot/vmlinux.bin
> > >   truncate: Invalid number: ‘arch/loongarch/boot/vmlinux.bin’
> > >   make[2]: *** [drivers/firmware/efi/libstub/Makefile.zboot:13:
> > >   arch/loongarch/boot/vmlinux.bin] Error 1
> > >   make[2]: *** Deleting file 'arch/loongarch/boot/vmlinux.bin'
> > >   make[1]: *** [arch/loongarch/Makefile:146: vmlinuz.efi] Error 2
> > >   make[1]: *** Waiting for unfinished jobs....
> > >   make: *** [Makefile:234: __sub-make] Error 2
> > >
> > > vmlinuz.efi depends on vmlinux.efi, but such a dependency is not
> > > specified in arch/loongarch/Makefile.
> > >
> > > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> > > ---
> > >
> > >  arch/loongarch/Makefile | 1 +
> > >  1 file changed, 1 insertion(+)
> > >
> > > diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
> > > index 9eeb0c05f3f4..6022bf3d30c9 100644
> > > --- a/arch/loongarch/Makefile
> > > +++ b/arch/loongarch/Makefile
> > > @@ -142,6 +142,7 @@ vdso-install-y += arch/loongarch/vdso/vdso.so.dbg
> > >
> > >  all:   $(notdir $(KBUILD_IMAGE))
> > >
> > > +vmlinuz.efi: vmlinux.efi
> > >  vmlinux.elf vmlinux.efi vmlinuz.efi: vmlinux
> > >         $(Q)$(MAKE) $(build)=$(boot) $(bootvars-y) $(boot)/$@
> > It is a little strange, because
> >
> > in drivers/firmware/efi/libstub/Makefile.zboot:
> > vmlinuz.efi depends on vmlinuz.efi.elf, vmlinuz.efi.elf depends on
> > vmlinuz.o, vmlinuz.o depends on vmlinuz, vmlinuz depends on
> > vmlinux.bin, vmlinux.bin depends on $(EFI_ZBOOT_PAYLOAD).
> >
> > in arch/loongarch/boot/Makefile,
> > EFI_ZBOOT_PAYLOAD := vmlinux.efi
> >
> > So I think vmlinuz.efi has already depend on vmlinux.efi.
>
>
>
> That is a story in arch/loongarch/boot/Makefile.
>
>
> I am talking about arch/loongarch/Makefile,
> which is included from the top Makefile.
>
>
> See this code.
>
>
> vmlinux.elf vmlinux.efi vmlinuz.efi: vmlinux
>         $(Q)$(MAKE) $(build)=$(boot) $(bootvars-y) $(boot)/$@
>
>
>
>
> Only the required dependency is
>
>  - vmlinux.elf depends on vmlinux
>  - vmlinuz.elf depends on vmlinux
>
>
> vmlinux.elf and vmlinuz.elf are independent of each other.
>
>
>
> In parallel building, GNU Make considers that
> vmlinux.elf and vmlinuz.elf can be built simultaneously.
>
>
> GNU Make spawns two processes to execute these simultaneously:
>
>  $(MAKE) $(build)=$(boot) $(bootvars-y) $(boot)/vmlinux.elf
>  $(MAKE) $(build)=$(boot) $(bootvars-y) $(boot)/vmlinuz.elf
>
>
>
> The former enters arch/loongarch/boot/Makefile to build
> vmlinux.elf.  (A)
>
>
> The latter also enters arch/loongarch/boot/Makefile to build
> vmlinuz.elf, which depends on vmlinux.elf  (B)
>
>
>
> (A) and (B) are independent processes, hence none of them
> know the other.
>
>
> I hope it is clearer.
Sorry, I'm not familiar with Makefile rules, so you are probably
right, but should we do it like this (remove the direct dependency
from vmlinuz.efi to vmlinux)?

vmlinuz.efi: vmlinux.efi
vmlinux.elf vmlinux.efi: vmlinux
        $(Q)$(MAKE) $(build)=$(boot) $(bootvars-y) $(boot)/$@

Huacai

>
>
>
>
>
>
> > Huacai
> >
> > >
> > > --
> > > 2.40.1
> > >
> > >
> >
>
>
> --
> Best Regards
> Masahiro Yamada

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