@loader_path - ShenYj/ShenYj.github.io GitHub Wiki

@loader_path

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

在此之后继续探索 @loader_path

实际场景为例: 我们的App链接了一个动态库，动态库中链接了另外一个动态库

最终生成的 test 可执行文件链接了 TestExample 这个动态库，TestExample 中又链接了 TestExampleLog 这个动态库

  • 目录结构

    .
├── Frameworks
│   └── TestExample.framework
│       ├── Frameworks
│       │   └── TestExampleLog.framework
│       │       ├── Headers
│       │       │   └── TestExampleLog.h
│       │       ├── TestExampleLog
│       │       ├── TestExampleLog.m
│       │       └── buildTestExampleLog.sh
│       ├── Headers
│       │   └── TestExample.h
│       ├── TestExample.m
│       └── buildTestExample.sh
├── build.sh
└── test.m

  • 代码

    test、TestExample、TestExampleLog

    • test.m

      #import <Foundation/Foundation.h>
#import "TestExample.h"
#import "TestExampleLog.h"

int main(){
    NSLog(@"testApp----");
    TestExample *manager = [TestExample new];
    [manager test: nil];
    TestExampleLog *log = [TestExampleLog new];
    NSLog(@"testApp----%@",log);
    return 0;
}

    • TestExample.h

      #import <Foundation/Foundation.h>

@interface TestExample : NSObject

- (void)test:(_Nullable id)e;

@end

    • TestExample.m

      #import "TestExample.h"
#import "TestExampleLog.h"

@implementation TestExample

- (void)test:(_Nullable id)e {
    NSLog(@"TestExample----");
    TestExampleLog *log = [TestExampleLog new];
    [log test_example_log: self];
}
@end

    • TestExampleLog.h

      #import <Foundation/Foundation.h>

@interface TestExampleLog : NSObject

- (void)test_example_log:(_Nullable id)e;

@end

    • TestExampleLog.m

      #import "TestExampleLog.h"

@implementation TestExampleLog

- (void)test_example_log:(_Nullable id)e {
    NSLog(@"TestExampleLog---%@", e);
}
@end

脚本

这里采取的链接器 Xlinker -install_name 的时候直接设置路径，免去了生成后在借助install_name_tool修改的环节

  • 脚本中重点关注 -Xlinker -install_name 的不同设置, 尤其是 buildTestExample.sh

  • buildTestExampleLog.sh

    clang -target x86_64-apple-macos12.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk \
-I./Headers \
-c TestExampleLog.m -o TestExampleLog.o

clang -dynamiclib  \
-target x86_64-apple-macos12.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk \
-Xlinker -install_name -Xlinker @rpath/TestExampleLog.framework/TestExampleLog \
TestExampleLog.o -o TestExampleLog

otool -l TestExampleLog | grep 'ID' -A 5
    buildTestExampleLog.sh 编译结果 
    ❯ ./buildTestExampleLog.sh
        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 948B94AA-6EB1-33A3-9BCE-D4F13B5A107D
Load command 10
    cmd LC_BUILD_VERSION
cmdsize 32

  • buildTestExample.sh

    clang -target x86_64-apple-macos12.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk \
-I./Headers \
-I./Frameworks/TestExampleLog.framework/Headers \
-c TestExample.m -o TestExample.o

clang -dynamiclib  \
-target x86_64-apple-macos12.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.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

echo "-------DYLIB---------"
otool -l TestExample | grep 'DYLIB' -A 5
echo "-------ID---------"
otool -l TestExample | grep 'ID' -A 5
    1. -Xlinker -install_name -Xlinker @rpath/TestExample.framework/TestExample
      • 给当前 TestExample 动态库配置 rpath
    2. -Xlinker -rpath -Xlinker @loader_path/Frameworks
      • 这一行是为了保证在 buildTestExample链接TestExampleLog时能够找到正确的路径, 为TestExampleLog补全前面的路径部分
      • 若此时使用 @executable_path 又要拼接中间这个动态库的路径
        可执行程序与TestExampleLog 之间隔着一个 TestExample动态库, 拼接起来不方便
        当然使用 @executable_path/Frameworks/TestExample.framework/Frameworks 也是没有问题的
      • 通过 @loader_path 就能很好的解决这个问题， 谁来链接 TestExampleLog，路径就代表谁
        • 在这个示例中 TestExample 链接了 TestExampleLog, 那么 @loader_path 就能代表 TestExample 所在的路径， 即 .../Frameworks/TestExample.framework
    3. -Xlinker -reexport_framework -Xlinker TestExampleLog 这里保证了可执行程序中能够直接调用 TestExampleLog 的方法
      • 在TestExample动态库中将TestExampleLog 重新导出放入 LC_REEXPORT_DYLIB，保证能够在可执行文件中直接调用到 TestExampleLog api
        • 可执行文件 --> LC_REEXPORT_DYLIB --> TestExampleLog 的符号
    buildTestExample.sh 编译结果 
    ❯ ./buildTestExample.sh
-------DYLIB---------
        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
--
        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 1856.105.0
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 1311.0.0
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 1856.105.0
compatibility version 150.0.0
-------ID---------
        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_UUID
cmdsize 24
    uuid 5F06CDBF-5B3C-3B62-ADFA-1C8EE11B6010
Load command 10
    cmd LC_BUILD_VERSION
cmdsize 32

  • build.sh

    clang -target x86_64-apple-macos12.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk \
-I./Frameworks/TestExample.framework/Headers \
-I./Frameworks/TestExample.framework/Frameworks/TestExampleLog.framework/Headers \
-c test.m -o test.o

clang   \
-target x86_64-apple-macos12.1 \
-fobjc-arc \
-isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX12.1.sdk \
-Xlinker -rpath -Xlinker @executable_path/Frameworks \
-F./Frameworks \
-framework TestExample \
test.o -o test

otool -l test | grep 'RPATH' -A 3
otool -l test | grep 'DYLIB' -A 3
    build.sh 编译结果 
    ❯ ./build.sh
        cmd LC_RPATH
    cmdsize 40
        path @executable_path/Frameworks (offset 12)
Load command 19
        cmd LC_LOAD_DYLIB
    cmdsize 72
        name @rpath/TestExample.framework/TestExample (offset 24)
time stamp 2 Thu Jan  1 08:00:02 1970
--
        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
--
        cmd LC_LOAD_DYLIB
    cmdsize 56
        name /usr/lib/libobjc.A.dylib (offset 24)
time stamp 2 Thu Jan  1 08:00:02 1970
--
        cmd LC_LOAD_DYLIB
    cmdsize 56
        name /usr/lib/libSystem.B.dylib (offset 24)
time stamp 2 Thu Jan  1 08:00:02 1970
--
        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

  • 最后通过 lldb 环境运行，在可执行文件中成功调用了两个动态库的方法

    ❯ lldb -file test
(lldb) target create "test"
Current executable set to '/Users/shenyj/Documents/CodeForTest/lib/loader_path/test' (x86_64).
(lldb) r
Process 5186 launched: '/Users/shenyj/Documents/CodeForTest/lib/loader_path/test' (x86_64)
2022-02-12 01:02:47.507558+0800 test[5186:3840218] testApp----
2022-02-12 01:02:47.507807+0800 test[5186:3840218] TestExample----
2022-02-12 01:02:47.507899+0800 test[5186:3840218] TestExampleLog---<TestExample: 0x600000010000>
2022-02-12 01:02:47.507927+0800 test[5186:3840218] testApp----<TestExampleLog: 0x600000010010>
Process 5186 exited with status = 0 (0x00000000)

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