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.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
Breno Leitao (4):
      bootconfig: return 0 from xbc_snprint_cmdline() for a leaf root
      bootconfig: render embedded bootconfig as a kernel cmdline at build time
      bootconfig: add xbc_prepend_embedded_cmdline() helper
      x86/setup: prepend embedded bootconfig cmdline before parse_early_param

 Makefile                   |  5 ++++
 arch/x86/Kconfig           |  1 +
 arch/x86/kernel/setup.c    |  3 +++
 include/linux/bootconfig.h |  7 ++++++
 init/Kconfig               | 33 ++++++++++++++++++++++++++
 init/main.c                | 19 ++++++++++++---
 lib/Makefile               | 16 +++++++++++++
 lib/bootconfig.c           | 58 ++++++++++++++++++++++++++++++++++++++++++++++
 lib/embedded-cmdline.S     | 16 +++++++++++++
 tools/bootconfig/Makefile  |  2 +-
 10 files changed, 156 insertions(+), 4 deletions(-)
---
base-commit: e7e28506af98ce4e1059e5ec59334b335c00a246
change-id: 20260508-bootconfig_using_tools-cfa7aa9d6a5a

Best regards,
--  
Breno Leitao <leitao@debian.org>

On Wed, 27 May 2026 09:41:33 -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.
> 

Thanks Breno, yes, that is what I think about.
Let me check it. And could you also check Sashiko's comments?

https://sashiko.dev/#/patchset/20260527-bootconfig_using_tools-v1-0-b6906a86e7d5%40debian.org

Thanks,

> Signed-off-by: Breno Leitao <leitao@debian.org>
> ---
> Breno Leitao (4):
>       bootconfig: return 0 from xbc_snprint_cmdline() for a leaf root
>       bootconfig: render embedded bootconfig as a kernel cmdline at build time
>       bootconfig: add xbc_prepend_embedded_cmdline() helper
>       x86/setup: prepend embedded bootconfig cmdline before parse_early_param
> 
>  Makefile                   |  5 ++++
>  arch/x86/Kconfig           |  1 +
>  arch/x86/kernel/setup.c    |  3 +++
>  include/linux/bootconfig.h |  7 ++++++
>  init/Kconfig               | 33 ++++++++++++++++++++++++++
>  init/main.c                | 19 ++++++++++++---
>  lib/Makefile               | 16 +++++++++++++
>  lib/bootconfig.c           | 58 ++++++++++++++++++++++++++++++++++++++++++++++
>  lib/embedded-cmdline.S     | 16 +++++++++++++
>  tools/bootconfig/Makefile  |  2 +-
>  10 files changed, 156 insertions(+), 4 deletions(-)
> ---
> base-commit: e7e28506af98ce4e1059e5ec59334b335c00a246
> change-id: 20260508-bootconfig_using_tools-cfa7aa9d6a5a
> 
> Best regards,
> --  
> Breno Leitao <leitao@debian.org>
> 


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

On Fri, May 29, 2026 at 12:15:19AM +0900, Masami Hiramatsu wrote:
> On Wed, 27 May 2026 09:41:33 -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.
> > 
> 
> Thanks Breno, yes, that is what I think about.
> Let me check it. And could you also check Sashiko's comments?

yes, I've spent some time on them, and it reported some good points, in
fact. I will fix those and resend.

Thanks!
--breno

On Fri, May 29, 2026 at 12:15:19AM +0000, Masami Hiramatsu wrote:
> On Wed, 27 May 2026 09:41:33 -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.
> > 
> 
> Thanks Breno, yes, that is what I think about.
> Let me check it. And could you also check Sashiko's comments?
> 
> https://sashiko.dev/#/patchset/20260527-bootconfig_using_tools-v1-0-b6906a86e7d5%40debian.org

Ack, I will have a look at them, thanks for confirming the direction is
correct.

--breno