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112 lines
4.4 KiB
112 lines
4.4 KiB
# 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/uapi/`
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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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* `external/kernel-headers/original/scsi/`
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Contains copies of the kernel scsi header files. These where never
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made into uapi files, but some user space code expects that these
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headers are available.
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* `external/kernel-headers/modified/scsi/`
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Contains hand-modified versions of a few files from `original/scsi/`
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that removes the kernel specific code from these files so they can
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be used as uapi headers. The tools to process the kernel headers will
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warn if any scsi header files have changed and require new versions
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to be hand-modified.
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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 Android mainline 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 https://android.googlesource.com/kernel/common/ -b android-mainline
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```
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The Android mainline kernel source has tags that indicate the kernel
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version to which they correspond. The format of a tag is
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android-mainline-XXX, where XXX is the kernel version. For example,
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android-mainline-5.10 corresponds to linux stable kernel 5.10. To check out
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a particular tag:
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```
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kernel_src> cd common
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kernel_src/common> git checkout tags/android-mainline-XXX
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```
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It is expected that a kernel update should only be performed on a valid tag.
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For testing purposes, it is possible that you can use the top of tree
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version, but never use that as the basis for importing new kernel headers.
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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 if there is a kernel source tree already checked out:
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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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Run this command to automatically download the latest version of the headers
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and import them if there is no checked out kernel source tree:
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```
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bionic/libc/kernel/tools/generate_uapi_headers.sh --download-kernel
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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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