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Documentation: kbuild: Update the debug information notes in reproducible-builds.rst

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The debug information part of the "Absolute filenames" section in the
reproducible builds document only mentions providing
'-fdebug-prefix-map' to KCFLAGS but it needs to be provided to KAFLAGS
as well since debug information has been generated for assembly files
for a long time.

Additionally, mention that the build directory may also appear as an
absolute path in the debug information (via DW_AT_comp_dir), so it needs
to be overridden via '-fdebug-prefix-map' as well.

Reported-by: Alexander Coffin <alex@cyberialabs.net>
Closes: https://lore.kernel.org/b8dfe7035d19fd611b9be55ee3145fdb@purelymail.com/
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Link: https://patch.msgid.link/20260313-kbuild-docs-repro-builds-fdebug-prefix-map-updates-v1-1-3aeeef7fa710@kernel.org
Signed-off-by: Nicolas Schier <nsc@kernel.org>
This commit is contained in:
Nathan Chancellor 2026-03-13 16:37:29 -07:00 • committed by Nicolas Schier
commit 2fb62d9154
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7
Documentation/kbuild/reproducible-builds.rst
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@ -50,8 +50,10 @@ Absolute filenames
------------------
When the kernel is built out-of-tree, debug information may include
absolute filenames for the source files. This must be overridden by
including the ``-fdebug-prefix-map`` option in the `KCFLAGS`_ variable.
absolute filenames for the source files and build directory. These must
be overridden by including a ``-fdebug-prefix-map`` option for each in
the `KCFLAGS`_ and `KAFLAGS`_ variables to cover both ``.c`` and ``.S``
files.
Depending on the compiler used, the ``__FILE__`` macro may also expand
to an absolute filename in an out-of-tree build. Kbuild automatically
@ -135,6 +137,7 @@ See ``scripts/setlocalversion`` for details.
.. _KBUILD_BUILD_TIMESTAMP: kbuild.html#kbuild-build-timestamp
.. _KBUILD_BUILD_USER and KBUILD_BUILD_HOST: kbuild.html#kbuild-build-user-kbuild-build-host
.. _KCFLAGS: kbuild.html#kcflags
.. _KAFLAGS: kbuild.html#kaflags
.. _prefix-map options: https://reproducible-builds.org/docs/build-path/
.. _Reproducible Builds project: https://reproducible-builds.org/
.. _SOURCE_DATE_EPOCH: https://reproducible-builds.org/docs/source-date-epoch/