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

Conor Dooley
2025-04-30T16:04:00Z

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+CC Palmer

On Tue, Mar 11, 2025 at 12:06:20PM +0100, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@kernel.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 running the risk of the data disappearing or being out of date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@kernel.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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