linux-kernel - Re: [PATCH v2] x86: Avoid relocation information in final vmlinux

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Message-ID: <16941b45-0f4f-e7c9-4602-d9acb0c612c3@suse.com>
Date:   Mon, 28 Nov 2022 15:38:08 +0100
From:   Petr Pavlu <petr.pavlu@...e.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, nicolas@...sle.eu,
        masahiroy@...nel.org, kirill.shutemov@...ux.intel.com,
        tony.luck@...el.com, michael.roth@....com, nathan@...nel.org,
        ndesaulniers@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86: Avoid relocation information in final vmlinux

On 11/25/22 20:25, Borislav Petkov wrote:
> On Tue, Sep 27, 2022 at 10:46:32AM +0200, Petr Pavlu wrote:
>> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
>> index 35ce1a64068b..eba7709d75ae 100644
>> --- a/arch/x86/boot/compressed/Makefile
>> +++ b/arch/x86/boot/compressed/Makefile
>> @@ -120,14 +120,12 @@ $(obj)/vmlinux.bin: vmlinux FORCE
>>  
>>  targets += $(patsubst $(obj)/%,%,$(vmlinux-objs-y)) vmlinux.bin.all vmlinux.relocs
>>  
>> -CMD_RELOCS = arch/x86/tools/relocs
>> -quiet_cmd_relocs = RELOCS  $@
>> -      cmd_relocs = $(CMD_RELOCS) $< > $@;$(CMD_RELOCS) --abs-relocs $<
>> -$(obj)/vmlinux.relocs: vmlinux FORCE
>> -	$(call if_changed,relocs)
>> +# vmlinux.relocs is created by the vmlinux postlink step.
>> +vmlinux.relocs: vmlinux
>> +	@true
>>  
>>  vmlinux.bin.all-y := $(obj)/vmlinux.bin
>> -vmlinux.bin.all-$(CONFIG_X86_NEED_RELOCS) += $(obj)/vmlinux.relocs
>> +vmlinux.bin.all-$(CONFIG_X86_NEED_RELOCS) += vmlinux.relocs
> 
> Any particular reason why vmlinux.relocs must move out of $(obj)/ where
> it resides now?

It looked slightly cleaner to me that Makefile.postlink generates
vmlinux.relocs at the same directory level where it is executed instead of
stuffing the file into arch/x86/boot/compressed. Makefile.postlink is invoked
in the context where it has no $(obj) variable set and has no immediate
knowledge about arch/x86/boot/compressed. It would also require that
Makefile.postlink makes first sure that this directory exists in the target
build tree as this step is run prior to arch/x86/boot/compressed/Makefile.

Let me know if this move of vmlinux.relocs is ok or if it would be preferred
to preserve its location.

With the move, the patch should be however at least updated to remove
vmlinux.relocs from arch/x86/boot/compressed/.gitignore, which I missed.

Thanks,
Petr