1.动态库原理
1.1自己生成动态库(失败)
我们还是用在静态库中的TestExample案例先生成动态库
image.png
为了方便我们使用创建build.sh，来使用脚本
clang -target x86_64-apple-macos11.0.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk \
-I./dylib \
-c test.m -o test.o
pushd ./dylib
echo "编译TestExample.m --- TestExample.o"
clang -target x86_64-apple-macos11.0.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk \
-c TestExample.m -o TestExample.o
clang -dynamiclib \
-target x86_64-apple-macos11.0.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk \
TestExample.o -o libTestExample.dylib
echo "编译TestExample.m --- libTestExample.dylib"
clang -target x86_64-apple-macos11.0.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk \
-L./dylib \
-lTestExample \
test.o -o test
运行后报错还是和上面一样 dyld: Library not loaded: libTestExample.dylib
1.2.先生成静态库再链接成动态库
//把我们的o文件变成a文件。也可以使用ar -rc a.a a.o
libtool -static -arch_only x86_64 TestExample.o -o libTestExample.a
ld -dylib -arch x86_64 \
-macosx_version_min 11.0 \
-syslibroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk \
-lsystem -framework Foundation \
-all_load \ //如果没有这个参数，链接器会默认not all load
libTestExample.a -o libTestExample.dylib
运行之后还是报错
Process 25266 launched: '/Users/MacW/Desktop/loginlearn/强化版/强化班-4-动态库/上课代码/动态库原理/test' (x86_64)
dyld: Library not loaded: libTestExample.dylib
Referenced from: /Users/MacW/Desktop/loginlearn/强化版/强化班-4-动态库/上课代码/动态库原理/test
Reason: image not found
错误显示库没有加载进来
我们查看test加载所需要的动态库
otool -l test | grep 'DYLIB' -A 5
//日志如下
cmd LC_LOAD_DYLIB
cmdsize 48
name libTestExample.dylib (offset 24)
time stamp 2 Thu Jan 1 08:00:02 1970
current version 0.0.0
compatibility version 0.0.0
--
cmd LC_LOAD_DYLIB
cmdsize 96
name /System/Library/Frameworks/Foundation.framework/Versions/C/Foundation (offset 24)
time stamp 2 Thu Jan 1 08:00:02 1970
current version 1770.106.0
compatibility version 300.0.0
--
cmd LC_LOAD_DYLIB
cmdsize 56
name /usr/lib/libobjc.A.dylib (offset 24)
time stamp 2 Thu Jan 1 08:00:02 1970
current version 228.0.0
compatibility version 1.0.0
--
cmd LC_LOAD_DYLIB
cmdsize 56
name /usr/lib/libSystem.B.dylib (offset 24)
time stamp 2 Thu Jan 1 08:00:02 1970
current version 1292.0.0
compatibility version 1.0.0
--
cmd LC_LOAD_DYLIB
cmdsize 104
name /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (offset 24)
time stamp 2 Thu Jan 1 08:00:02 1970
current version 1770.106.0
compatibility version 150.0.0
我们看到我们自己创建的库 name libTestExample.dylib (offset 24)，而其他的动态库的name确实库的路径。
我们的动态库能够自己保存自己的路径
otool -l ./dylib/libTestExample.dylib | grep 'ID' -A 5
//-A是向下寻找5行，-B是向上查找
cmd LC_ID_DYLIB
cmdsize 48
name libTestExample.dylib (offset 24)
time stamp 1 Thu Jan 1 08:00:01 1970
current version 0.0.0
compatibility version 0.0.0
--
cmd LC_UUID
cmdsize 24
uuid F26CDB5B-F71B-3658-86BE-C93CBE279ABE
Load command 9
cmd LC_BUILD_VERSION
cmdsize 32
我们看到name 还是 libTestExample.dylib
我们可以使用install_name_tool去给动态库添加路径
man install_name_tool
NAME
install_name_tool - change dynamic shared library install names
install_name_tool就是改变动态的路径。
给动态路添加路径
install_name_tool -id /Users/MacW/Desktop/loginlearn/强化版/强化班-4-动态库/上课代码/动态库原理/dylib/libTestExample.dylib libTestExample.dylib
重新查看动态库的LC_ID_DYLIB
otool -l libTestExample.dylib | grep 'ID' -A 5
cmd LC_ID_DYLIB
cmdsize 144
name /Users/MacW/Desktop/loginlearn/强化版/强化班-4-动态库/上课代码/动态库原理/dylib/libTestExample.dylib (offset 24)
time stamp 1611538070 Mon Jan 25 09:27:50 2021
current version 0.0.0
compatibility version 0.0.0
--
cmd LC_UUID
cmdsize 24
uuid F26CDB5B-F71B-3658-86BE-C93CBE279ABE
Load command 9
cmd LC_BUILD_VERSION
cmdsize 32
然后重新编译和链接我们的test文件运行成功
我们通过install_name_tool，重新给编译过的动态库加的路径，其实ld提供给我们一个参数可以直接加的install_name
所以我们初期的sh脚本如下
clang -target x86_64-apple-macos11.0.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk \
-I./dylib \
-c test.m -o test.o
pushd ./dylib
echo "编译TestExample.m --- TestExample.o"
clang -target x86_64-apple-macos11.0.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk \
-c TestExample.m -o TestExample.o
echo "编译TestExample.o --- libTestExample.a"
# Xcode->静态库
libtool -static -arch_only x86_64 TestExample.o -o libTestExample.a
# -dynamiclib: 动态库
# dylib 最终链接产物 -》
ld -dylib -arch x86_64 \
-macosx_version_min 11.0 \
-syslibroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk \
-lsystem -framework Foundation \
-install_name /Users/MacW/Desktop/loginlearn/强化版/强化班-4-动态库/上课代码/动态库原理/dylib/libTestExample.dylib \
-all_load \
libTestExample.a -o libTestExample.dylib
popd
echo "链接libTestExample.dylib -- test EXEC"
clang -target x86_64-apple-macos11.0.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk \
-L./dylib \
-lTestExample \
test.o -o test
运行没问题
2.动态库复用性
我们在上面指定的路径是我们的绝对路径，如果动态库换了位置，很明显还是会出现之前出现的问题， Reason: image not found
2.1@rpath解决绝对路径的困扰
@rpath
Runpath search Paths
dyld搜索路径
运行时@rpath指示dyld按顺序搜索路径列表，以找到动态库。
@rpath保存一个或多个路径的变量
所以我们修改脚本
-install_name @rpath/dylib/libTestExample.dylib
运行还是报错，为什么呢？我们可以查看test文件是否有rpath的设置
2.2 rpath
otool -l test | grep 'RPATH' -A 5
我们通过install_name_tool给test添加rpath路径
install_name_tool -add_rpath /Users/MacW/Desktop/loginlearn/强化版/强 化班-4-动态库/上课代码/动态库原理 test
正常运行。但是add_rpath也是我们手动添加的，没有可复用性。
2.3.executable_path和loader_path
@executable_path:表示可执行程序所在的目录，解析为可执行文件的绝对路径。
@loader_path:表示被加载的Mach-O 所在的目录，每次加载时，都可能 被设置为不同的路径，由上层指定。
install_name_tool -rpath /Users/MacW/Desktop/loginlearn/强化版/强化班-4-动态库/上课代码/动态库原理 @executable_path test
运行test成功
3.动态库链接动态库
test.m文件使用Frameworks中的TestExample.framework
在TestExample.framework库中使用TestExampleLog.framework
3.1先编译并链接TestExampleLog.framework
clang -target x86_64-apple-macos11.0.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk \
-I./Headers \
-c TestExampleLog.m -o TestExampleLog.o
clang -dynamiclib \
-target x86_64-apple-macos11.0.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk \
-Xlinker -install_name -Xlinker @rpath/TestExampleLog.framework/TestExampleLog \
TestExampleLog.o -o TestExampleLog
install_name是提供给外部需要链接TestExampleLog的路径。
通过查看otool -l TestExampleLog | grep 'ID' -A 5能看出外部需要链接的路径
cmd LC_ID_DYLIB
cmdsize 72
name @rpath/TestExampleLog.framework/TestExampleLog (offset 24)
time stamp 1 Thu Jan 1 08:00:01 1970
current version 0.0.0
compatibility version 0.0.0
--
cmd LC_UUID
cmdsize 24
uuid 73F8F987-0378-346D-B014-890611B76871
Load command 9
cmd LC_BUILD_VERSION
cmdsize 32
3.2.再编译链接TestExample.framework
clang -target x86_64-apple-macos11.0.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk \
-I./Headers \
-I./Frameworks/TestExampleLog.framework/Headers \
-c TestExample.m -o TestExample.o
clang -dynamiclib \
-target x86_64-apple-macos11.0.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk \
-Xlinker -install_name -Xlinker @rpath/TestExample.framework/TestExample \
-Xlinker -rpath -Xlinker @loader_path/Frameworks \
-F./Frameworks \
-framework TestExampleLog \
TestExample.o -o TestExample
echo "-------DYLIB---------"
otool -l TestExample | grep 'DYLIB' -A 5
echo "-------ID---------"
otool -l TestExample | grep 'ID' -A 5
install_name是提供给调用者加载的路径
rpath是提供给调用TestExampleLog的初始路径
3.3编译并链接test
clang -target x86_64-apple-macos11.0.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk \
-I./Frameworks/TestExample.framework/Headers \
-c test.m -o test.o
clang \
-target x86_64-apple-macos11.0.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk \
-Xlinker -rpath -Xlinker @executable_path/Frameworks \
-F./Frameworks \
-framework TestExample \
test.o -o test
运行正常打印
3.4.test文件怎么使用TestExampleLog
如果我们想使用TestExampleLog，我们需要能再TestExample中导出符号中能看到TestExampleLog
objdump --macho --exports-trie TestExample
TestExample:
Exports trie:
0x000080C0 _OBJC_METACLASS_$_TestExample
0x000080E8 _OBJC_CLASS_$_TestExample
我们没有看出有导出符号，所以我们无法在test使用TestExampleLog，我们需要使用reexport_framework
我们修改TestExample内的脚本
clang -dynamiclib \
-target x86_64-apple-macos11.0.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk \
-Xlinker -install_name -Xlinker @rpath/TestExample.framework/TestExample \
-Xlinker -rpath -Xlinker @loader_path/Frameworks \
-Xlinker -reexport_framework -Xlinker TestExampleLog \
-F./Frameworks \
-framework TestExampleLog \
TestExample.o -o TestExample
查看DYLIIB信息
otool -l TestExample | grep 'DYLIB' -A 5
cmd LC_ID_DYLIB
cmdsize 72
name @rpath/TestExample.framework/TestExample (offset 24)
time stamp 1 Thu Jan 1 08:00:01 1970
current version 0.0.0
compatibility version 0.0.0
--
cmd LC_REEXPORT_DYLIB
cmdsize 72
name @rpath/TestExampleLog.framework/TestExampleLog (offset 24)
time stamp 2 Thu Jan 1 08:00:02 1970
current version 0.0.0
compatibility version 0.0.0
可以知道TestExample重新加一个cmd，LC_REEXPORT_DYLIB
我们在test中导入头文件
#import <Foundation/Foundation.h>
#import "TestExample.h"
#import "TestExampleLog.h"
int main(){
NSLog(@"testApp----");
TestExample *manager = [TestExample new];
[manager lg_test: nil];
TestExampleLog *log = [TestExampleLog new];
NSLog(@"testApp----%@",log);
return 0;
}
我们的脚本文件也需要-I头文件，重新运行脚本，正常打印。
