782c485880
There's no need to check in generated code. Test: builds & boots Change-Id: Ife368bca4349d4adeb0666db590356196b4fbd63
85 lines
3.1 KiB
Markdown
85 lines
3.1 KiB
Markdown
# Bionic Kernel Header Files
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Bionic comes with a processed set of all of the uapi Linux kernel headers that
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can safely be included by userland applications and libraries.
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These clean headers are automatically generated by several scripts located
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in the `tools/` directory. The tools process the original
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unmodified kernel headers in order to get rid of many annoying
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declarations and constructs that usually result in compilation failure.
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The 'clean headers' only contain type and macro definitions, with the
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exception of a couple static inline functions used for performance
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reason (e.g. optimized CPU-specific byte-swapping routines).
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They can be included from C++, or when compiling code in strict ANSI mode.
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They can be also included before or after any Bionic C library header.
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Description of the directories involved in generating the parsed kernel headers:
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* `external/kernel-headers/original/`
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Contains the uapi kernel headers found in the android kernel. Note this
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also includes the header files that are generated by building the kernel
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sources.
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* `bionic/libc/kernel/uapi/`
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Contains the cleaned kernel headers and mirrors the directory structure
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in `external/kernel-headers/original/uapi/`.
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* `bionic/libc/kernel/tools/`
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Contains various Python and shell scripts used to get and re-generate
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the headers.
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The tools to get/parse the headers:
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* `tools/generate_uapi_headers.sh`
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Checks out the android kernel and generates all uapi header files.
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copies all the changed files into external/kernel-headers.
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* `tools/clean_header.py`
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Prints the clean version of a given kernel header. With the -u option,
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this will also update the corresponding clean header file if its
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content has changed. You can also process more than one file with -u.
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* `tools/update_all.py`
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Automatically update all clean headers from the content of
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`external/kernel-headers/original/`.
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## How To Update The Headers
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IMPORTANT IMPORTANT:
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WHEN UPDATING THE HEADERS, ALWAYS CHECK THAT THE NEW CLEAN HEADERS DO
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NOT BREAK THE KERNEL <-> USER ABI, FOR EXAMPLE BY CHANGING THE SIZE
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OF A GIVEN TYPE. THIS TASK CANNOT BE EASILY AUTOMATED AT THE MOMENT.
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Download the Linux kernel source code:
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```
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> mkdir kernel_src
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> cd kernel_src
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kernel_src> git clone git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
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```
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Then checkout the stable tag for the new kernel headers to import:
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```
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kernel_src> cd linux-stable
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kernel_src/linux-stable> git checkout tags/vXXX
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```
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Before running the command to import the headers, make sure that you have
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done a lunch TARGET. The script uses a variable set by the lunch command
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to determine which directory to use as the destination directory.
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After running lunch, run this command to import the headers into the android
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source tree:
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```
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bionic/libc/kernel/tools/generate_uapi_headers.sh --use-kernel-dir kernel_src
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```
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Next, run this command to copy the parsed files to bionic/libc/kernel/uapi:
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```
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bionic/libc/kernel/tools/update_all.py
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```
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After this, you will need to build/test the tree to make sure that these
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changes do not introduce any errors.
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