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Christopher Ferris 3fc4e11607 Add support for removing structs that cross blocks. 
The latest kernel has a struct that needs to be removed,
but the struct crosses blocks. Add support for removing a
struct that does cross blocks. This support is very primitive,
and will not parse any really complicated struct that uses
defines in complicated ways.

Combine the kernel_structs_to_remove and kernel_struct_replacements
structure into a single map. This allows marking a structure
to be removed as replaced with an #include <bits/STRUCT.h>.

The new support for the remove of structures is all in the
removeStructs function.

Raise an exception if the struct parsing does not work properly.

Add new unit tests for all of the new code.

In addition, fix the algorithm for deleting the uapi directory
before it gets updated. A new file BUILD was checking in that
directory, so delete everything in the directory except that
BUILD file.

Test: Unit tests pass.
Test: Running update_all.py results in the no unexpected changes.
Change-Id: I9a8cef0321beaf71d03b5b874327747a7edb6119
2022-08-09 17:49:31 -07:00
..
android Declare libc's contributions to API surface(s) in Multi-tree 2022-06-29 20:40:11 +00:00
tools Add support for removing structs that cross blocks. 2022-08-09 17:49:31 -07:00
uapi Declare libc's contributions to API surface(s) in Multi-tree 2022-06-29 20:40:11 +00:00
.clang-format Fully disable clang format where needed. 2020-01-30 08:10:17 -08:00
README.md Update kernel update documentation. 2021-03-18 00:38:34 -07:00

README.md

Bionic Kernel Header Files

Bionic comes with a processed set of all of the uapi Linux kernel headers that can safely be included by userland applications and libraries.

These clean headers are automatically generated by several scripts located in the tools/ directory. The tools process the original unmodified kernel headers in order to get rid of many annoying declarations and constructs that usually result in compilation failure.

The 'clean headers' only contain type and macro definitions, with the exception of a couple static inline functions used for performance reason (e.g. optimized CPU-specific byte-swapping routines).

They can be included from C++, or when compiling code in strict ANSI mode. They can be also included before or after any Bionic C library header.

Description of the directories involved in generating the parsed kernel headers:

  • external/kernel-headers/original/uapi/ Contains the uapi kernel headers found in the Android kernel. Note this also includes the header files that are generated by building the kernel sources.

  • external/kernel-headers/original/scsi/ Contains copies of the kernel scsi header files. These where never made into uapi files, but some user space code expects that these headers are available.

  • external/kernel-headers/modified/scsi/ Contains hand-modified versions of a few files from original/scsi/ that removes the kernel specific code from these files so they can be used as uapi headers. The tools to process the kernel headers will warn if any scsi header files have changed and require new versions to be hand-modified.

  • bionic/libc/kernel/uapi/ Contains the cleaned kernel headers and mirrors the directory structure in external/kernel-headers/original/uapi/.

  • bionic/libc/kernel/tools/ Contains various Python and shell scripts used to get and re-generate the headers.

The tools to get/parse the headers:

  • tools/generate_uapi_headers.sh Checks out the Android kernel and generates all uapi header files. copies all the changed files into external/kernel-headers.

  • tools/clean_header.py Prints the clean version of a given kernel header. With the -u option, this will also update the corresponding clean header file if its content has changed. You can also process more than one file with -u.

  • tools/update_all.py Automatically update all clean headers from the content of external/kernel-headers/original/.

How To Update The Headers

IMPORTANT IMPORTANT:

WHEN UPDATING THE HEADERS, ALWAYS CHECK THAT THE NEW CLEAN HEADERS DO NOT BREAK THE KERNEL <-> USER ABI, FOR EXAMPLE BY CHANGING THE SIZE OF A GIVEN TYPE. THIS TASK CANNOT BE EASILY AUTOMATED AT THE MOMENT.

Download the Android mainline kernel source code:

  > mkdir kernel_src
  > cd kernel_src
  kernel_src> git clone https://android.googlesource.com/kernel/common/ -b android-mainline

The Android mainline kernel source has tags that indicate the kernel version to which they correspond. The format of a tag is android-mainline-XXX, where XXX is the kernel version. For example, android-mainline-5.10 corresponds to linux stable kernel 5.10. To check out a particular tag:

  kernel_src> cd common
  kernel_src/common> git checkout tags/android-mainline-XXX

It is expected that a kernel update should only be performed on a valid tag. For testing purposes, it is possible that you can use the top of tree version, but never use that as the basis for importing new kernel headers.

Before running the command to import the headers, make sure that you have done a lunch TARGET. The script uses a variable set by the lunch command to determine which directory to use as the destination directory.

After running lunch, run this command to import the headers into the Android source tree if there is a kernel source tree already checked out:

  bionic/libc/kernel/tools/generate_uapi_headers.sh --use-kernel-dir kernel_src

Run this command to automatically download the latest version of the headers and import them if there is no checked out kernel source tree:

  bionic/libc/kernel/tools/generate_uapi_headers.sh --download-kernel

Next, run this command to copy the parsed files to bionic/libc/kernel/uapi:

  bionic/libc/kernel/tools/update_all.py

After this, you will need to build/test the tree to make sure that these changes do not introduce any errors.