linux-kernel - Re: [PATCH 1/3] kernel/Kconfig.kexec: drop select of KEXEC for CRASH

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Message-ID: <ZV8yi86cA5mhYNll@MiWiFi-R3L-srv>
Date:   Thu, 23 Nov 2023 19:07:55 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Ignat Korchagin <ignat@...udflare.com>
Cc:     linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-s390@...r.kernel.org,
        akpm@...ux-foundation.org, eric_devolder@...oo.com,
        kernel-team <kernel-team@...udflare.com>
Subject: Re: [PATCH 1/3] kernel/Kconfig.kexec: drop select of KEXEC for
 CRASH_DUMP

On 11/23/23 at 08:23am, Ignat Korchagin wrote:
> On Thu, Nov 23, 2023 at 7:37 AM Baoquan He <bhe@...hat.com> wrote:
> >
> > Ignat Korchagin complained that a potential config regression was
> > introduced by commit 89cde455915f ("kexec: consolidate kexec and
> > crash options into kernel/Kconfig.kexec"). Before the commit,
> > CONFIG_CRASH_DUMP has no dependency on CONFIG_KEXEC. After the commit,
> > CRASH_DUMP selects KEXEC. That enforces system to have CONFIG_KEXEC=y
> > as long as CONFIG_CRASH_DUMP=Y which people may not want.
> >
> > In Ignat's case, he sets CONFIG_CRASH_DUMP=y, CONFIG_KEXEC_FILE=y and
> > CONFIG_KEXEC=n because kexec_load interface could have security issue if
> > kernel/initrd has no chance to be signed and verified.
> >
> > CRASH_DUMP has select of KEXEC because Eric, author of above commit,
> > met a LKP report of build failure when posting patch of earlier version.
> > Please see below link to get detail of the LKP report:
> >
> >     https://lore.kernel.org/all/3e8eecd1-a277-2cfb-690e-5de2eb7b988e@oracle.com/T/#u
> >
> > In fact, that LKP report is triggered because arm's <asm/kexec.h> is
> > wrapped in CONFIG_KEXEC ifdeffery scope. That is wrong. CONFIG_KEXEC
> > controls the enabling/disabling of kexec_load interface, but not kexec
> > feature. Removing the wrongly added CONFIG_KEXEC ifdeffery scope in
> > <asm/kexec.h> of arm allows us to drop the select KEXEC for CRASH_DUMP.
> 
> Hm... With the patch, when cross compiling for arm and
> CONFIG_KEXEC_CORE=y
> # CONFIG_KEXEC is not set
> CONFIG_CRASH_DUMP=y
> 
> I get the following linker error at the end:
> 
>   CALL    scripts/checksyscalls.sh
>   UPD     include/generated/utsversion.h
>   CC      init/version-timestamp.o
>   LD      .tmp_vmlinux.kallsyms1
> arm-linux-gnueabi-ld: kernel/kexec_core.o: in function `kimage_free':
> kexec_core.c:(.text+0xf5c): undefined reference to `machine_kexec_cleanup'
> arm-linux-gnueabi-ld: kernel/kexec_core.o: in function `__crash_kexec':
> kexec_core.c:(.text+0x15bc): undefined reference to `machine_crash_shutdown'
> arm-linux-gnueabi-ld: kexec_core.c:(.text+0x15c4): undefined reference
> to `machine_kexec'
> arm-linux-gnueabi-ld: kernel/kexec_core.o: in function `kernel_kexec':
> kexec_core.c:(.text+0x1a04): undefined reference to `machine_kexec'
> make[2]: *** [scripts/Makefile.vmlinux:37: vmlinux] Error 1
> make[1]: *** [/home/ignat/git/linux-upstream/Makefile:1154: vmlinux] Error 2
> make: *** [Makefile:234: __sub-make] Error 2

Oops, I forgot this part. This should fix the link error.

diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index d53f56d6f840..771264d4726a 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -59,7 +59,7 @@ obj-$(CONFIG_FUNCTION_TRACER)	+= entry-ftrace.o
 obj-$(CONFIG_DYNAMIC_FTRACE)	+= ftrace.o insn.o patch.o
 obj-$(CONFIG_FUNCTION_GRAPH_TRACER)	+= ftrace.o insn.o patch.o
 obj-$(CONFIG_JUMP_LABEL)	+= jump_label.o insn.o patch.o
-obj-$(CONFIG_KEXEC)		+= machine_kexec.o relocate_kernel.o
+obj-$(CONFIG_KEXEC_CORE)	+= machine_kexec.o relocate_kernel.o
 # Main staffs in KPROBES are in arch/arm/probes/ .
 obj-$(CONFIG_KPROBES)		+= patch.o insn.o
 obj-$(CONFIG_OABI_COMPAT)	+= sys_oabi-compat.o