Rob Landley | 451ad11 | 2007-10-16 23:31:16 -0700 | [diff] [blame] | 1 | Exporting kernel headers for use by userspace |
| 2 | ============================================= |
| 3 | |
| 4 | The "make headers_install" command exports the kernel's header files in a |
| 5 | form suitable for use by userspace programs. |
| 6 | |
| 7 | The linux kernel's exported header files describe the API for user space |
| 8 | programs attempting to use kernel services. These kernel header files are |
| 9 | used by the system's C library (such as glibc or uClibc) to define available |
| 10 | system calls, as well as constants and structures to be used with these |
| 11 | system calls. The C library's header files include the kernel header files |
| 12 | from the "linux" subdirectory. The system's libc headers are usually |
| 13 | installed at the default location /usr/include and the kernel headers in |
| 14 | subdirectories under that (most notably /usr/include/linux and |
| 15 | /usr/include/asm). |
| 16 | |
| 17 | Kernel headers are backwards compatible, but not forwards compatible. This |
| 18 | means that a program built against a C library using older kernel headers |
| 19 | should run on a newer kernel (although it may not have access to new |
| 20 | features), but a program built against newer kernel headers may not work on an |
| 21 | older kernel. |
| 22 | |
| 23 | The "make headers_install" command can be run in the top level directory of the |
| 24 | kernel source code (or using a standard out-of-tree build). It takes two |
| 25 | optional arguments: |
| 26 | |
Anish Bhatt | ed45d40 | 2015-06-08 17:37:31 -0700 | [diff] [blame^] | 27 | make headers_install ARCH=i386 INSTALL_HDR_PATH=/usr |
Rob Landley | 451ad11 | 2007-10-16 23:31:16 -0700 | [diff] [blame] | 28 | |
| 29 | ARCH indicates which architecture to produce headers for, and defaults to the |
| 30 | current architecture. The linux/asm directory of the exported kernel headers |
| 31 | is platform-specific, to see a complete list of supported architectures use |
| 32 | the command: |
| 33 | |
| 34 | ls -d include/asm-* | sed 's/.*-//' |
| 35 | |
Anish Bhatt | ed45d40 | 2015-06-08 17:37:31 -0700 | [diff] [blame^] | 36 | INSTALL_HDR_PATH indicates where to install the headers. It defaults to |
| 37 | "./usr". |
| 38 | |
| 39 | An 'include' directory is automatically created inside INSTALL_HDR_PATH and |
| 40 | headers are installed in 'INSTALL_HDR_PATH/include'. |
Rob Landley | 451ad11 | 2007-10-16 23:31:16 -0700 | [diff] [blame] | 41 | |
| 42 | The command "make headers_install_all" exports headers for all architectures |
| 43 | simultaneously. (This is mostly of interest to distribution maintainers, |
| 44 | who create an architecture-independent tarball from the resulting include |
Kirill A. Shutemov | f682030 | 2010-12-13 19:10:28 +0200 | [diff] [blame] | 45 | directory.) You also can use HDR_ARCH_LIST to specify list of architectures. |
| 46 | Remember to provide the appropriate linux/asm directory via "mv" or "ln -s" |
| 47 | before building a C library with headers exported this way. |
Rob Landley | 451ad11 | 2007-10-16 23:31:16 -0700 | [diff] [blame] | 48 | |
| 49 | The kernel header export infrastructure is maintained by David Woodhouse |
| 50 | <dwmw2@infradead.org>. |