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

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Message-ID: <Z7y_i-ySL68BfkgQ@gmail.com>
Date: Mon, 24 Feb 2025 19:51:35 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Ard Biesheuvel <ardb+git@...gle.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
	linux-kbuild@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step


* 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

Nice! Does this also result in any measurable speedup of the build, or 
are the steps still similar?

But in terms of justification for upstreaming, the reduction in 
complexity alone makes it worth it IMO:

  19 files changed, 52 insertions(+), 87 deletions(-)

Thanks,

	Ingo