编译库是添加-fPIC选项的方式及验证

编译库是添加-fPIC选项的方式及验证

1.CMakeLists.txt中的合适位置添加：

SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fPIC")
SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fPIC")

合适的位置可以理解为不影响其他组件编译的位置，或者用cmake宏可以控制的位置；

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2.Makefile中， 查找DEBUG_CFLAGS、RELEASE_CFLAGS或CFLAGS、CXXFLAGS（CPPFLAGS），在其后添加**-fPIC**；

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3.configure中，先运行指令**./configure --help**，然后查看C compiler flags对应的名称，先正确使用configure生成makefile，然后在makefile中修改，如下：
（1）运行./configure --help进行查找得到：
（2）生成makefile后，进行关键字（CFLAGS和CXXFLAGS）查找，添加**-fPIC**即可：

第一步：
  CC          C compiler command
  CFLAGS      C compiler flags
  LDFLAGS     linker flags, e.g. -L if you have libraries in a
              nonstandard directory 
  LIBS        libraries to pass to the linker, e.g. -l
  CPPFLAGS    C/C++/Objective C preprocessor flags, e.g. -I if
              you have headers in a nonstandard directory 
  CXX         C++ compiler command
  CXXFLAGS    C++ compiler flags

第二步：
AWK = gawk
CC = gcc
CCDEPMODE = depmode=gcc3
CFLAGS = -g -fPIC -O2 -Wall -fno-strict-aliasing -pthread
CPP = gcc -E
CPPFLAGS = -fPIC
CYGPATH_W = echo
DEFS = -DHAVE_CONFIG_H
DEPDIR = .deps
DLLTOOL = false

4.编译出静态库后验证-fPIC选项是否添加成功：

readelf --relocs 静态库路径 | egrep '(GOT|PLT|JU?MP_SLOT)'

eg：

相对路径：readelf --relocs libtinyxml.a | egrep '(GOT|PLT|JU?MP_SLOT)'
绝对路径：readelf --relocs /chenbin/3th_library/jsoncpp-1.8.4/build/install/lib64/libjsoncpp_static.a| egrep '(GOT|PLT|JU?MP_SLOT)'

如果运行指令后控制台输出不为空，则表示添加选项成功，如下所示：

[root@localhost build]# readelf --relocs /chenbin/3th_library/jsoncpp-1.8.4/build/install/lib64/libjsoncpp_static.a| egrep '(GOT|PLT|JU?MP_SLOT)'
000000000000  00a600000137 R_AARCH64_ADR_GOT 0000000000000000 _ZTVN4Json17CharReader + 0
000000001aec  00a600000137 R_AARCH64_ADR_GOT 0000000000000000 _ZTVN4Json17CharReader + 0
000000003130  011400000137 R_AARCH64_ADR_GOT 0000000000000000 _ZTVN4Json13OurCharRea + 0
000000003448  012900000137 R_AARCH64_ADR_GOT 0000000000000000 _ZTVSt9basic_iosIcSt11 + 0
000000003460  012b00000137 R_AARCH64_ADR_GOT 0000000000000000 _ZTTNSt7__cxx1119basic + 0
0000000034b4  00ec00000137 R_AARCH64_ADR_GOT 0000000000000000 _ZTVSt15basic_streambu + 0
0000000034bc  012d00000137 R_AARCH64_ADR_GOT 0000000000000000 _ZTVNSt7__cxx1119basic + 0
0000000034cc  00eb00000137 R_AARCH64_ADR_GOT 0000000000000000 _ZTVNSt7__cxx1115basic + 0
000000003694  012b00000137 R_AARCH64_ADR_GOT 0000000000000000 _ZTTNSt7__cxx1119basic + 0
0000000038d8  013500000137 R_AARCH64_ADR_GOT 0000000000000000 _ZN4Json5Value14maxLar + 0
00000000396c  013600000137 R_AARCH64_ADR_GOT 0000000000000000 _ZN4Json5Value6maxIntE + 0
0000000039f8  013800000137 R_AARCH64_ADR_GOT 0000000000000000 _ZN4Json5Value13maxLar + 0
000000003a3c  013900000137 R_AARCH64_ADR_GOT 0000000000000000 _ZN4Json5Value13minLar + 0
...
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