linux-kernel - Re: Regression. -6.3.X Good. -6.4-rcY Bad.

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Message-ID: <CAKbZUD3FBiaLGWq=TipfevqXP0SBz8F+=L6JSO+FMZOv0QQ9AQ@mail.gmail.com>
Date:   Mon, 22 May 2023 02:15:13 +0100
From:   Pedro Falcato <pedro.falcato@...il.com>
To:     Bagas Sanjaya <bagasdotme@...il.com>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Build System <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Regressions <regressions@...ts.linux.dev>,
        Linux EFI <linux-efi@...r.kernel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alan Bartlett <ajb@...epo.org>
Subject: Re: Regression. -6.3.X Good. -6.4-rcY Bad.

On Mon, May 22, 2023 at 1:43 AM Bagas Sanjaya <bagasdotme@...il.com> wrote:
>
> Hi,
>
> I notice a simple build-time regression on Bugzilla [1]. Quoting from it:
>
> > This is a very simple to see regression.
> >
> > On arm64 hardware, take any one of the -6.4-rcY tarballs created by Linus. Extract the contents of the tarball and cd to the linux-6.4-rcY directory. Issue a "make clean" or a "make mrproper" or a "make distclean" command. Look at the output (there should not be any). In every case, the output is --
> >
> > nm: 'vmlinux': No such file
> >
> > A bisection of Linus' full tree was performed specifying v6.4-rc1 as bad and v6.3 as good. Here is the result --
> >
> > git bisect start
> > # status: waiting for both good and bad commits
> > # bad: [ac9a78681b921877518763ba0e89202254349d1b] Linux 6.4-rc1
> > git bisect bad ac9a78681b921877518763ba0e89202254349d1b
> > # status: waiting for good commit(s), bad commit known
> > # good: [457391b0380335d5e9a5babdec90ac53928b23b4] Linux 6.3
> > git bisect good 457391b0380335d5e9a5babdec90ac53928b23b4
> > # good: [6e98b09da931a00bf4e0477d0fa52748bf28fcce] Merge tag 'net-next-6.4' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next
> > git bisect good 6e98b09da931a00bf4e0477d0fa52748bf28fcce
> > # good: [70cc1b5307e8ee3076fdf2ecbeb89eb973aa0ff7] Merge tag 'powerpc-6.4-1' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux
> > git bisect good 70cc1b5307e8ee3076fdf2ecbeb89eb973aa0ff7
> > # bad: [865fdb08197e657c59e74a35fa32362b12397f58] Merge tag 'input-for-v6.4-rc0' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input
> > git bisect bad 865fdb08197e657c59e74a35fa32362b12397f58
> > # good: [e81507acdc19d91df4121f409871f3e4e055f6c2] Merge tag 'clk-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/clk/linux
> > git bisect good e81507acdc19d91df4121f409871f3e4e055f6c2
> > # bad: [26c009dffca89b0f8fe7facc41d1ccf88a66825a] Merge tag '6.4-rc-smb3-client-fixes-part1' of git://git.samba.org/sfrench/cifs-2.6
> > git bisect bad 26c009dffca89b0f8fe7facc41d1ccf88a66825a
> > # bad: [10de638d8ea57ebab4231ea077bed01d9bade775] Merge tag 's390-6.4-1' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux
> > git bisect bad 10de638d8ea57ebab4231ea077bed01d9bade775
> > # good: [680957b3b8b0b2e8697592fcb77369d4f643908a] s390/relocate_kernel: use SYM* macros instead of ENTRY(), etc.
> > git bisect good 680957b3b8b0b2e8697592fcb77369d4f643908a
> > # good: [ea76e08f4d901a450619831a255e9e0a4c0ed162] rust: ioctl: Add ioctl number manipulation functions
> > git bisect good ea76e08f4d901a450619831a255e9e0a4c0ed162
> > # bad: [825a0714d2b3883d4f8ff64f6933fb73ee3f1834] Merge tag 'efi-next-for-v6.4' of git://git.kernel.org/pub/scm/linux/kernel/git/efi/efi
> > git bisect bad 825a0714d2b3883d4f8ff64f6933fb73ee3f1834
> > # good: [9489d1bdb763a3dd954e61522043190a9fd1cb4c] power: supply: generic-adc-battery: simplify read_channel logic
> > git bisect good 9489d1bdb763a3dd954e61522043190a9fd1cb4c
> > # good: [528bd42615f4bb564613cc76dead90d7fbae76ba] power: supply: rk817: Drop unneeded debugging code
> > git bisect good 528bd42615f4bb564613cc76dead90d7fbae76ba
> > # good: [538bc0f40b364f2c7b81f11aa163f723b138b40f] efi/zboot: Set forward edge CFI compat header flag if supported
> > git bisect good 538bc0f40b364f2c7b81f11aa163f723b138b40f
> > # bad: [026b85796ab4d52af56f8a1c60d2613983ecd845] efi/zboot: arm64: Grab code size from ELF symbol in payload
> > git bisect bad 026b85796ab4d52af56f8a1c60d2613983ecd845
> > # bad: [45dd403da851124412d32e3193c21de4a51d29da] efi/zboot: arm64: Inject kernel code size symbol into the zboot payload
> > git bisect bad 45dd403da851124412d32e3193c21de4a51d29da
> > # first bad commit: [45dd403da851124412d32e3193c21de4a51d29da] efi/zboot: arm64: Inject kernel code size symbol into the zboot payload
> >
> > Reverting the commit 45dd403da851124412d32e3193c21de4a51d29da resolves the problem.
>
> The regression looks like arm-specific, but the first bad commit
> IMO isn't related to kbuild system.
>
> Anyway, I'm adding it to regzbot:
>
> #regzbot introduced: 45dd403da85112 https://bugzilla.kernel.org/show_bug.cgi?id=217468
> #regzbot title: nm vmlinux ENOENT when "make mrproper" on arm64

I was able to track down the issue.
In line 47, arch/arm64/boot/Makefile, a variable (that gets expanded
on use, hence = and not :=) gets defined, that requires vmlinux to
exist (see the $(shell) invocation).
drivers/firmware/efi/libstub/Makefile.zboot then defines a variable
with :=, which expands on site and not when it actually needs to be
used. This expands EFI_ZBOOT_OBJCOPY_FLAGS without vmlinux existing,
which ENOENTs.

The below patch should fix it. I'm not submitting an actual patch
because I simply don't know if there are any possible side effects
here (although it frankly seems unlikely).

diff --git a/drivers/firmware/efi/libstub/Makefile.zboot
b/drivers/firmware/efi/libstub/Makefile.zboot
index 89ef820f3b3..3fb39dea114 100644
--- a/drivers/firmware/efi/libstub/Makefile.zboot
+++ b/drivers/firmware/efi/libstub/Makefile.zboot
@@ -32,7 +32,7 @@ zboot-size-len-$(CONFIG_KERNEL_GZIP)   := 0
 $(obj)/vmlinuz: $(obj)/vmlinux.bin FORCE
        $(call if_changed,$(zboot-method-y))

-OBJCOPYFLAGS_vmlinuz.o := -I binary -O $(EFI_ZBOOT_BFD_TARGET)
$(EFI_ZBOOT_OBJCOPY_FLAGS) \
+OBJCOPYFLAGS_vmlinuz.o = -I binary -O $(EFI_ZBOOT_BFD_TARGET)
$(EFI_ZBOOT_OBJCOPY_FLAGS) \
                          --rename-section
.data=.gzdata,load,alloc,readonly,contents
 $(obj)/vmlinuz.o: $(obj)/vmlinuz FORCE
        $(call if_changed,objcopy)



-- 
Pedro