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([2405:201:31:d01f:a107:5c92:b303:910a]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c79216ff41dsm3142863a12.2.2026.04.10.15.13.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 10 Apr 2026 15:13:06 -0700 (PDT) From: Piyush Patle To: Nathan Chancellor , Nicolas Schier , Jonathan Corbet , linux-kbuild@vger.kernel.org, linux-doc@vger.kernel.org Cc: Shuah Khan , Mark Rutland , Chen Pei , Randy Dunlap , Arnd Bergmann , Masahiro Yamada , linux-kernel@vger.kernel.org Subject: [PATCH] kbuild: document generation of offset header files Date: Sat, 11 Apr 2026 03:42:54 +0530 Message-ID: <20260410221257.191517-1-piyushpatle228@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Replace the placeholder reference with a description of how Kbuild generates offset header files such as include/generated/asm-offsets.h. Remove the corresponding TODO entry now that this is documented. Signed-off-by: Piyush Patle --- Documentation/kbuild/makefiles.rst | 41 ++++++++++++++++++++++++------ 1 file changed, 33 insertions(+), 8 deletions(-) diff --git a/Documentation/kbuild/makefiles.rst b/Documentation/kbuild/makefiles.rst index 24a4708d26e8..7521cae7d56f 100644 --- a/Documentation/kbuild/makefiles.rst +++ b/Documentation/kbuild/makefiles.rst @@ -1285,8 +1285,39 @@ Example:: In this example, the file target maketools will be processed before descending down in the subdirectories. -See also chapter XXX-TODO that describes how kbuild supports -generating offset header files. +Generating offset header files +------------------------------ + +The ``include/generated/asm-offsets.h`` header exposes C structure +member offsets and other compile-time constants to assembly code. It +is generated from ``arch/$(SRCARCH)/kernel/asm-offsets.c``. + +The source file uses ``DEFINE()``, ``OFFSET()``, ``BLANK()`` and +``COMMENT()`` from ````. These emit marker strings +through inline asm that Kbuild extracts from the compiled assembly +output. + +Example:: + + #include + #include + + int main(void) + { + OFFSET(TSK_ACTIVE_MM, task_struct, active_mm); + DEFINE(THREAD_SIZE, THREAD_SIZE); + BLANK(); + return 0; + } + +The rules are defined in the top-level ``Kbuild`` and +``scripts/Makefile.lib``. The header is built during Kbuild's +``prepare`` phase, after ``archprepare`` and before descending into +subdirectories. + +The same mechanism generates ``include/generated/bounds.h`` from +``kernel/bounds.c`` and ``include/generated/rq-offsets.h`` from +``kernel/sched/rq-offsets.c``. List directories to visit when descending ----------------------------------------- @@ -1690,9 +1721,3 @@ Credits - Updates by Kai Germaschewski - Updates by Sam Ravnborg - Language QA by Jan Engelhardt - -TODO -==== - -- Generating offset header files. -- Add more variables to chapters 7 or 9? -- 2.43.0