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

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Message-ID: <CAK7LNATb40pkqXXH+o_CXW6Vf3zavAj8oSeWnpGfXq6SCto4kw@mail.gmail.com>
Date: Tue, 11 Mar 2025 11:38:46 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Ingo Molnar <mingo@...nel.org>, Ard Biesheuvel <ardb@...nel.org>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, linux-kbuild@...r.kernel.org, 
	Linus Torvalds <torvalds@...ux-foundation.org>, Peter Zijlstra <peterz@...radead.org>, 
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH 0/4] x86/build: Get rid of vmlinux postlink step

On Sun, Mar 9, 2025 at 6:48 PM Ingo Molnar <mingo@...nel.org> wrote:
>
>
> * Ard Biesheuvel <ardb@...nel.org> wrote:
>
> > On Sat, 8 Mar 2025 at 17:17, Masahiro Yamada <masahiroy@...nel.org> wrote:
> > >
> > ...
> > > I do not think it is broken.
> > > As I mentioned above, I regard vmlinux.relocs as a byproduct
> > > of the atomic build rule of vmlinux. This works.
>
> Except when it doesn't work, such as when an intermediate linking step
> fails, and intermediate build products are lost and cannot be recreated
> easily (or at all without modifying the source)?
>
> And the thing is, there should be no such thing as an 'atomic build
> rule of vmlinux' if it means lost information when the build is broken
> at an intermediate step. What purpose does it have?
>
> > There is no make rule for vmlinux.relocs, and so
> >
> > - if it gets deleted, it cannot be rebuilt and even though the build
> > does not break, the relocation data is missing from the compressed
> > image, and this could potentially break the kaslr startup code,
> > - it vmlinux.relocs is older than vmlinux for some reason, make will
> > not notice and silently reuse the outdated version,
> > - when creating vmlinux.relocs from vmlinux and an error occurs,
> > vmlinux is deleted, making it difficult to diagnose the problem.
> >
> > I think this is badly broken, but if you think this is all working as
> > it should, I am not going to debate this further, and you can consider
> > the patch series withdrawn.
>
> That's very sad, as both the simplification is substantial:
>
>   19 files changed, 52 insertions(+), 87 deletions(-)
>
> and the increase in debuggability is substantial as well.
>
> Thanks,
>
>         Ingo

When a byproduct is accidentally lost
(for example, manually deleted), it is not automatically restored.
Running 'rm vmlinux' or 'make clean' is needed.

vmlinux.relocs is one such byproduct.
Another is the map file when CONFIG_VMLINUX_MAP=y is enabled.

I am a bit concerned about having more and more
intermediate vmlinux.* files, but maybe only me.
I hope vmlinux.unstripped is the only/last one.


OK, let's do this.

Ard, please send v2 with .gitignore and 'clean' target updates.


--
Best Regards
Masahiro Yamada