linux-kernel - Re: [RFC PATCH] kbuild: Make --build-id linker flag configurable

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Message-ID: <cd0e4ca5-542c-42db-bd7c-c63f5df85fc5@linux.microsoft.com>
Date: Tue, 3 Feb 2026 11:58:51 +0530
From: Naman Jain <namjain@...ux.microsoft.com>
To: Nathan Chancellor <nathan@...nel.org>,
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Nicolas Schier <nsc@...nel.org>, Catalin Marinas
 <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Andy Lutomirski <luto@...nel.org>, Thomas Gleixner <tglx@...nel.org>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 "H . Peter Anvin" <hpa@...or.com>, Masahiro Yamada <masahiroy@...nel.org>,
 Miguel Ojeda <ojeda@...nel.org>, Tamir Duberstein <tamird@...il.com>,
 Steven Rostedt <rostedt@...dmis.org>, Kees Cook <kees@...nel.org>,
 Ard Biesheuvel <ardb@...nel.org>, linux-kbuild@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 Saurabh Singh Sengar <ssengar@...ux.microsoft.com>
Subject: Re: [RFC PATCH] kbuild: Make --build-id linker flag configurable

On 2/3/2026 4:45 AM, Nathan Chancellor wrote:
> On Mon, Feb 02, 2026 at 03:15:30PM +0100, Thomas Weißschuh wrote:
>> On Mon, Feb 02, 2026 at 11:06:31AM +0000, Naman Jain wrote:
>>> I am trying to implement reproducible builds for one of my product
>>> kernel. I referred https://reproducible-builds.org/docs/build-path/
>>> and tried to use both -fdebug-prefix-map=OLD=NEW and
>>> -fmacro-prefix-map=OLD=NEW, but still could not achieve bit by bit
>>> binary reproducibility without overwriting build-id to none.
>>> If I move the kernel to same path in other setup, I was able to create
>>> same binary hash, however, without it, there is some difference in
>>> build-id hash values.
>>
>> Can you force the same build path during package building?
>> That should avoid this issue.
> 
> Yeah, I think that it would be better to document this in
> Documentation/kbuild/reproducible-builds.rst, as opposed to adding a
> hack to disable the build ID altogether. It seems easy enough to make
> the paths consistent between machines and environments by using a
> container or such. The new scripts/container in -next could help there.
> 
> Cheers,
> Nathan

Thank you Nathan for your inputs.

I'll plan to ensure same path for my kernel build, and send a patch to 
add this in reproducible builds documentation.

--- a/Documentation/kbuild/reproducible-builds.rst
+++ b/Documentation/kbuild/reproducible-builds.rst
@@ -58,6 +58,9 @@ to an absolute filename in an out-of-tree build. 
Kbuild automatically
  uses the ``-fmacro-prefix-map`` option to prevent this, if it is
  supported.

+If it still does not work, ensure that the kernel is built in the same
+directory, using containers or such.
+
  The Reproducible Builds web site has more information about these
  `prefix-map options`_.

Regards,
Naman