Linux build：头文件安装

文章目录

• [1. 前言](#1. 前言)
• [2. 安装头文件](#2. 安装头文件)

1. 前言

限于作者能力水平，本文可能存在谬误，因此而给读者带来的损失，作者不做任何承诺。

2. 安装头文件

Linux 通过下面的命令

$ make ARCH=arm headers_install

导出头文件给用户空间，通常是给 glibc 这样的库使用，但用户空间程序也可以直接使用。

先看 linux/Makefile：

...

PHONY += __headers
__headers: $(version_h) scripts_basic uapi-asm-generic archheaders archscripts
	$(Q)$(MAKE) $(build)=scripts build_unifdef

...

PHONY += headers_install
headers_install: __headers
	$(if $(wildcard $(srctree)/arch/$(hdr-arch)/include/uapi/asm/Kbuild),, \
	  $(error Headers not exportable for the $(SRCARCH) architecture))
	$(Q)$(MAKE) $(hdr-inst)=include/uapi dst=include
	$(Q)$(MAKE) $(hdr-inst)=arch/$(hdr-arch)/include/uapi $(hdr-dst)

具体的安装操作见 ./scripts/Makefile.headersinst：

# SPDX-License-Identifier: GPL-2.0
# ==========================================================================
# Installing headers
#
# All headers under include/uapi, include/generated/uapi,
# arch/<arch>/include/uapi and arch/<arch>/include/generated/uapi are
# exported.
# They are preprocessed to remove __KERNEL__ section of the file.
#
# ==========================================================================

PHONY := __headers
__headers:

include scripts/Kbuild.include

srcdir        := $(srctree)/$(obj)

# When make is run under a fakechroot environment, the function
# $(wildcard $(srcdir)/*/.) doesn't only return directories, but also regular
# files. So, we are using a combination of sort/dir/wildcard which works
# with fakechroot.
subdirs       := $(patsubst $(srcdir)/%/,%,\
		 $(filter-out $(srcdir)/,\
		 $(sort $(dir $(wildcard $(srcdir)/*/)))))

# Recursion
__headers: $(subdirs)

.PHONY: $(subdirs)
$(subdirs):
	$(Q)$(MAKE) $(hdr-inst)=$(obj)/$@ dst=$(dst)/$@

# Skip header install/check for include/uapi and arch/$(hdr-arch)/include/uapi.
# We have only sub-directories there.
skip-inst := $(if $(filter %/uapi,$(obj)),1)

ifeq ($(skip-inst),)

# Kbuild file is optional
kbuild-file := $(srctree)/$(obj)/Kbuild
-include $(kbuild-file)

installdir    := $(INSTALL_HDR_PATH)/$(dst)
gendir        := $(objtree)/$(subst include/,include/generated/,$(obj))
header-files  := $(notdir $(wildcard $(srcdir)/*.h))
header-files  += $(notdir $(wildcard $(srcdir)/*.agh))
header-files  := $(filter-out $(no-export-headers), $(header-files))
genhdr-files  := $(notdir $(wildcard $(gendir)/*.h))
genhdr-files  := $(filter-out $(header-files), $(genhdr-files))

# files used to track state of install/check
install-file  := $(installdir)/.install
check-file    := $(installdir)/.check

# all headers files for this dir
all-files     := $(header-files) $(genhdr-files)
output-files  := $(addprefix $(installdir)/, $(all-files))

ifneq ($(mandatory-y),)
missing       := $(filter-out $(all-files),$(mandatory-y))
ifneq ($(missing),)
$(error Some mandatory headers ($(missing)) are missing in $(obj))
endif
endif

# Work out what needs to be removed
oldheaders    := $(patsubst $(installdir)/%,%,$(wildcard $(installdir)/*.h))
unwanted      := $(filter-out $(all-files),$(oldheaders))

# Prefix unwanted with full paths to $(INSTALL_HDR_PATH)
unwanted-file := $(addprefix $(installdir)/, $(unwanted))

printdir = $(patsubst $(INSTALL_HDR_PATH)/%/,%,$(dir $@))

quiet_cmd_install = INSTALL $(printdir) ($(words $(all-files))\
                            file$(if $(word 2, $(all-files)),s))
      cmd_install = \
        $(CONFIG_SHELL) $< $(installdir) $(srcdir) $(header-files); \
        $(CONFIG_SHELL) $< $(installdir) $(gendir) $(genhdr-files); \
        touch $@

quiet_cmd_remove = REMOVE  $(unwanted)
      cmd_remove = rm -f $(unwanted-file)

quiet_cmd_check = CHECK   $(printdir) ($(words $(all-files)) files)
# Headers list can be pretty long, xargs helps to avoid
# the "Argument list too long" error.
      cmd_check = for f in $(all-files); do                          \
                  echo "$(installdir)/$${f}"; done                      \
                  | xargs                                            \
                  $(PERL) $< $(INSTALL_HDR_PATH)/include $(SRCARCH); \
	          touch $@

ifndef HDRCHECK
# Rules for installing headers
__headers: $(install-file)
	@:

targets += $(install-file)
$(install-file): scripts/headers_install.sh \
		 $(addprefix $(srcdir)/,$(header-files)) \
		 $(addprefix $(gendir)/,$(genhdr-files)) FORCE
	$(if $(unwanted),$(call cmd,remove),)
	$(if $(wildcard $(dir $@)),,$(shell mkdir -p $(dir $@)))
	$(call if_changed,install)

else
__headers: $(check-file)
	@:

targets += $(check-file)
$(check-file): scripts/headers_check.pl $(output-files) FORCE
	$(call if_changed,check)

endif

targets := $(wildcard $(sort $(targets)))
cmd_files := $(wildcard \
             $(foreach f,$(targets),$(dir $(f)).$(notdir $(f)).cmd))

ifneq ($(cmd_files),)
	include $(cmd_files)
endif

endif # skip-inst

.PHONY: $(PHONY)
PHONY += FORCE
FORCE: ;

可以看到，安装下面这 4个目录下的头文件：

# 公用 UAPI 头文件
include/uapi
include/generated/uapi # 编译时生成
# 架构 UAPI 头文件
arch/$(hdr-arch)/include/uapi # 如 arch/arm/include/uapi
arch/<arch>/include/generated/uapi # 编译时生成

./scripts/Makefile.headersinst 调用 scripts/headers_install.sh 进行头文件安装，默认安装在 linux/usr 目录下，生成一个 linux/usr/include 文件夹，其中包含所有安装的头文件。

看看4个安装目录下都有哪些头文件：

# 这个有点多，就不用 tree 命令展开了
$ ls include/uapi
asm-generic  drm  linux  misc  mtd  rdma  scsi  sound  video  xen

$ tree include/generated/uapi/
include/generated/uapi/
└── linux
    └── version.h

1 directory, 1 file

$ tree arch/arm/include/uapi
arch/arm/include/uapi
└── asm
    ├── auxvec.h
    ├── byteorder.h
    ├── fcntl.h
    ├── hwcap.h
    ├── ioctls.h
    ├── Kbuild
    ├── kvm.h
    ├── kvm_para.h
    ├── mman.h
    ├── perf_regs.h
    ├── posix_types.h
    ├── ptrace.h
    ├── setup.h
    ├── sigcontext.h
    ├── signal.h
    ├── statfs.h
    ├── stat.h
    ├── swab.h
    ├── types.h
    └── unistd.h

1 directory, 20 files
asm

$ tree arch/arm/include/generated/uapi
arch/arm/include/generated/uapi
└── asm
    ├── bitsperlong.h
    ├── errno.h
    ├── ioctl.h
    ├── ipcbuf.h
    ├── msgbuf.h
    ├── param.h
    ├── poll.h
    ├── resource.h
    ├── sembuf.h
    ├── shmbuf.h
    ├── siginfo.h
    ├── socket.h
    ├── sockios.h
    ├── termbits.h
    ├── termios.h
    ├── unistd-common.h
    ├── unistd-eabi.h
    └── unistd-oabi.h

1 directory, 18 files

看一下安装过程：

$ make ARCH=arm headers_install
  CHK     include/generated/uapi/linux/version.h
  HOSTCC  scripts/unifdef
  INSTALL usr/include/asm-generic/ (36 files)
  INSTALL usr/include/drm/ (25 files)
  INSTALL usr/include/linux/ (485 files)
  INSTALL usr/include/linux/android/ (1 file)
  INSTALL usr/include/linux/byteorder/ (2 files)
  INSTALL usr/include/linux/caif/ (2 files)
  INSTALL usr/include/linux/can/ (6 files)
  INSTALL usr/include/linux/cifs/ (1 file)
  INSTALL usr/include/linux/dvb/ (8 files)
  INSTALL usr/include/linux/genwqe/ (1 file)
  INSTALL usr/include/linux/hdlc/ (1 file)
  INSTALL usr/include/linux/hsi/ (2 files)
  INSTALL usr/include/linux/iio/ (2 files)
  INSTALL usr/include/linux/isdn/ (1 file)
  INSTALL usr/include/linux/mmc/ (1 file)
  INSTALL usr/include/linux/netfilter/ (87 files)
  INSTALL usr/include/linux/netfilter/ipset/ (4 files)
  INSTALL usr/include/linux/netfilter_arp/ (2 files)
  INSTALL usr/include/linux/netfilter_bridge/ (17 files)
  INSTALL usr/include/linux/netfilter_ipv4/ (9 files)
  INSTALL usr/include/linux/netfilter_ipv6/ (12 files)
  INSTALL usr/include/linux/nfsd/ (5 files)
  INSTALL usr/include/linux/raid/ (2 files)
  INSTALL usr/include/linux/sched/ (1 file)
  INSTALL usr/include/linux/spi/ (1 file)
  INSTALL usr/include/linux/sunrpc/ (1 file)
  INSTALL usr/include/linux/tc_act/ (15 files)
  INSTALL usr/include/linux/tc_ematch/ (4 files)
  INSTALL usr/include/linux/usb/ (12 files)
  INSTALL usr/include/linux/wimax/ (1 file)
  INSTALL usr/include/misc/ (1 file)
  INSTALL usr/include/mtd/ (5 files)
  INSTALL usr/include/rdma/ (20 files)
  INSTALL usr/include/rdma/hfi/ (2 files)
  INSTALL usr/include/scsi/ (4 files)
  INSTALL usr/include/scsi/fc/ (4 files)
  INSTALL usr/include/sound/ (15 files)
  INSTALL usr/include/video/ (3 files)
  INSTALL usr/include/xen/ (4 files)
  INSTALL usr/include/asm/ (37 files)

默认在 linux/usr 目录下，创建 linux/usr/include 目录，然后安装所有 UAPI 头文件。为什么只安装 uapi 目录下头文件？因为 linux uapi 目录 下头文件就是导出给用户使用的，其它的头文件不应该导出，是不对用户开放的黑盒子。

另外，可以通过 INSTALL_HDR_PATH 将头文件安装到指定目录：

$ make ARCH=arm INSTALL_HDR_PATH=<target-path> headers_install

同样会在 <target-path> 目录下创建 <target-path>/include 文件夹安装所有头文件。另外，O= 参数也是支持的，如：

$ make ARCH=arm O=output headers_install

则会在 output/usr/include 目录下安装所有头文件。当然，也可以同时使用 INSTALL_HDR_PATH= 和 O= 参数：

$ make ARCH=arm O=output INSTALL_HDR_PATH=<target-path> headers_install

最后，还可以通过命令：

$ make headers_install_all

安装所有架构的头文件。

调试可以加上 V=1 参数。