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

[Nathan Chancellor]

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@xxxxxxxxxxxxxxx>
Closes: https://lore.kernel.org/b8dfe7035d19fd611b9be55ee3145fdb@xxxxxxxxxxxxxx/
Signed-off-by: Nathan Chancellor <nathan@xxxxxxxxxx>
---
 Documentation/kbuild/reproducible-builds.rst | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/Documentation/kbuild/reproducible-builds.rst b/Documentation/kbuild/reproducible-builds.rst
index 96d208e578cd..bc1eb82211df 100644
--- a/Documentation/kbuild/reproducible-builds.rst
+++ b/Documentation/kbuild/reproducible-builds.rst
@@ -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/

---
base-commit: 1f318b96cc84d7c2ab792fcc0bfd42a7ca890681
change-id: 20260313-kbuild-docs-repro-builds-fdebug-prefix-map-updates-c4c3c4d69550

Best regards,
--  
Nathan Chancellor <nathan@xxxxxxxxxx>