linux-kernel - Re: [PATCH v2 3/4] Kbuild: Create intermediate vmlinux build with relocations preserved

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Message-ID: <20250430-bronze-unsuited-3f47ce46d8d2@spud>
Date: Wed, 30 Apr 2025 17:03:56 +0100
From: Conor Dooley <conor@...nel.org>
To: Ard Biesheuvel <ardb+git@...gle.com>
Cc: linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
	x86@...nel.org, Ard Biesheuvel <ardb@...nel.org>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Ingo Molnar <mingo@...nel.org>, palmer@...belt.com
Subject: Re: [PATCH v2 3/4] Kbuild: Create intermediate vmlinux build with
 relocations preserved

+CC Palmer

On Tue, Mar 11, 2025 at 12:06:20PM +0100, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@...nel.org>
> 
> The imperative paradigm used to build vmlinux, extract some info from it
> or perform some checks on it, and subsequently modify it again goes
> against the declarative paradigm that is usually employed for defining
> make rules.
> 
> In particular, the Makefile.postlink files that consume their input via
> an output rule result in some dodgy logic in the decompressor makefiles
> for RISC-V and x86, given that the vmlinux.relocs input file needed to
> generate the arch-specific relocation tables may not exist or be out of
> date, but cannot be constructed using the ordinary Make dependency based
> rules, because the info needs to be extracted while vmlinux is in its
> ephemeral, non-stripped form.
> 
> So instead, for architectures that require the static relocations that
> are emitted into vmlinux when passing --emit-relocs to the linker, and
> are subsequently stripped out again, introduce an intermediate vmlinux
> target called vmlinux.unstripped, and organize the reset of the build
> logic accordingly:
> 
> - vmlinux.unstripped is created only once, and not updated again
> - build rules under arch/*/boot can depend on vmlinux.unstripped without
>   running the risk of the data disappearing or being out of date
> - the final vmlinux generated by the build is not bloated with static
>   relocations that are never needed again after the build completes.
> 
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>

Delayed report since I have been slacking on my testing, but looks like
this has broken boot for me on riscv (mpfs-icicle-kit), no output after
"Starting kernel", defconfig should be:
https://raw.githubusercontent.com/ConchuOD/riscv-env/refs/heads/dev/conf/defconfig
Toolchain is llvm 16. LMK if there's some salient info missing.

Cheers,
Conor.

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