linux-kernel - Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

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Message-ID: <CAMj1kXHamiZ8u4YO9FnrWhpcotUkAusDF_db_5H2qaVD85qmVA@mail.gmail.com>
Date: Thu, 6 Mar 2025 17:47:33 +0100
From: Ard Biesheuvel <ardb@...nel.org>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, linux-kbuild@...r.kernel.org, 
	Masahiro Yamada <masahiroy@...nel.org>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

On Mon, 24 Feb 2025 at 14:21, Ard Biesheuvel <ardb+git@...gle.com> wrote:
>
> From: Ard Biesheuvel <ardb@...nel.org>
>
> Kbuild supports an architecture specific Makefile.postlink file that is
> invoked for the vmlinux target after it has been built. This Makefile
> takes 'vmlinux' (which has just been built) as the target, and mangles
> the file and/or constructs other intermediate artifacts from it.
>
> This violates the general philosophy of Make, which is based on rules
> and dependencies, and artifacts that are rebuilt only when any of their
> dependencies have been updated.
>
> Instead, the different incarnations of vmlinux that are consumed by
> different stages of the build should be emitted as distinct files, where
> rules and dependencies are used to define one in terms of the other.
>
> This also works around an error observed here [0], where vmlinux is
> deleted by Make because a subsequent step that consumes it as input
> throws an error.
>
> So refactor the vmlinux shell scripts and build rules so that
> architectures that rely on --emit-relocs to construct vmlinux with
> static relocations preserved will get a separate vmlinux.unstripped file
> carrying those relocations. This removes the need for an imperative
> postlink step, given that any rules that depend on the unstripped
> vmlinux can now simply depend on vmlinux.unstripped, rather than inject
> a build step into Makefile.postlink
>
> S390 should be able to do the same. MIPS and RISC-V perform some
> post-build checks on vmlinux, which is reasonable in principle for a
> postlink step, although deleting vmlinux when the check fails is equally
> unhelpful.
>
> [0] https://lore.kernel.org/all/Z5ARucnUgqjwBnrp@gmail.com/T/#m731ed0206949fc3f39fcc8a7b82fe348a8fc80c4
>
> Cc: Masahiro Yamada <masahiroy@...nel.org>
> Cc: Ingo Molnar <mingo@...nel.org>
>
> Ard Biesheuvel (4):
>   Kbuild/link-vmlinux.sh: Make output file name configurable
>   Kbuild: Introduce Kconfig symbol for linking vmlinux with relocations
>   Kbuild: Create intermediate vmlinux build with relocations preserved
>   x86: Get rid of Makefile.postlink
>

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