Re: [PATCH v3 0/6] bootconfig: embed kernel.* cmdline at build time

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Mon, 08 Jun 2026 09:23:57 -0700
Breno Leitao <leitao@debian.org> wrote:

> The userspace pieces (xbc_snprint_cmdline() in lib/, tools/bootconfig -C)
> already landed; this series wires the rendered cmdline into the kernel.
> 
> Motivation: today the embedded bootconfig is parsed at runtime, after
> parse_early_param() has already run, so early_param() handlers can't
> see embedded values. Folding the kernel.* subtree into the cmdline at
> build time gives a CONFIG_CMDLINE-equivalent for embedded-bootconfig
> users without forcing them to maintain two cmdline sources.
> 
> Behaviorally, the "kernel" subtree is rendered to a flat string at
> build time and stashed in .init.rodata. setup_arch() prepends it to
> boot_command_line before parse_early_param() runs. Overflow is a soft
> error: the helper logs and leaves boot_command_line untouched rather
> than panicking, so an oversized embedded bconf cannot brick a boot.
> 

Sashiko still leaves some comments. 
https://sashiko.dev/#/patchset/20260608-bootconfig_using_tools-v3-0-4ddd079a0696%40debian.org

BTW, can you also update the document (Documentation/admin-guide/bootconfig.rst)
about what is the expected behavior of this feature (kconfigs, examples)?

Thank you,


> Signed-off-by: Breno Leitao <leitao@debian.org>
> ---
> Changes in v3:
> - Patch 3: Move HOSTCC override to the kernel-side rule; tool keeps
>   $(CC) for standalone/cross builds.
> - Patch 6: Drop the false fail-safe wording; document the
>   BOOT_CONFIG_FORCE=y default interaction.
> - Link to v2:
>   https://lore.kernel.org/r/20260605-bootconfig_using_tools-v2-0-d309f544b5f7@debian.org
> 
> Changes in v2 (addressing review of v1):
> - Split out a standalone fix for the NULL-pointer arithmetic in
>   xbc_snprint_cmdline() so the build-time render cannot trip host
>   UBSan/FORTIFY_SOURCE.
> - Rework the leaf-root handling: instead of returning early, skip @root
>   inside the loop so a root carrying both a value and subkeys
>   (kernel = x together with kernel.foo = bar) still renders its
>   descendant keys.
> - Build tools/bootconfig with $(HOSTCC) so cross-compiled (ARCH=...)
>   builds render the cmdline on the build host instead of failing with
>   "Exec format error".
> - Mark the embedded cmdline section read-only (drop the "w" flag from
>   .init.rodata).
> - Add a make-clean hook so tools/bootconfig artifacts are removed by
>   make clean.
> - Gate the x86 prepend on "bootconfig" being present on the command
>   line (or CONFIG_BOOT_CONFIG_FORCE), matching the init.* opt-in
>   semantics documented in bootconfig.rst and preserving fail-safe
>   recovery: dropping "bootconfig" from the bootloader cmdline now also
>   disables the embedded kernel.* keys.
> - Link to v1: https://patch.msgid.link/20260527-bootconfig_using_tools-v1-0-b6906a86e7d5@debian.org
> 
> ---
> Breno Leitao (6):
>       bootconfig: fix NULL-pointer arithmetic in xbc_snprint_cmdline()
>       bootconfig: render descendant keys when xbc_snprint_cmdline() root has a value
>       bootconfig: render embedded bootconfig as a kernel cmdline at build time
>       bootconfig: clean build-time tools/bootconfig from make clean
>       bootconfig: add xbc_prepend_embedded_cmdline() helper
>       x86/setup: prepend embedded bootconfig cmdline before parse_early_param
> 
>  MAINTAINERS                |   1 +
>  Makefile                   |  24 +++++++++-
>  arch/x86/Kconfig           |   1 +
>  arch/x86/kernel/setup.c    |  16 +++++++
>  include/linux/bootconfig.h |   9 ++++
>  init/Kconfig               |  36 +++++++++++++++
>  init/main.c                |  25 ++++++++--
>  lib/Makefile               |  16 +++++++
>  lib/bootconfig.c           | 112 ++++++++++++++++++++++++++++++++++++++++++---
>  lib/embedded-cmdline.S     |  16 +++++++
>  tools/bootconfig/Makefile  |   4 +-
>  11 files changed, 247 insertions(+), 13 deletions(-)
> ---
> base-commit: e7e28506af98ce4e1059e5ec59334b335c00a246
> change-id: 20260508-bootconfig_using_tools-cfa7aa9d6a5a
> 
> Best regards,
> -- 
> Breno Leitao <leitao@debian.org>
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>