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