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