OS X 和 Android 共享库中覆盖弱函数的不同行为 [英] Different behavior of override weak function in shared library between OS X and Android
问题描述
我在 OS X 和 Android 之间遇到了不同的行为:
I am encountering a different behavior between OS X and Android:
- 我的共享库中有一个弱函数
foo
, - 我想用我的可执行文件中定义的强函数覆盖它.
- 我希望被覆盖的也会影响库内的调用
结果:我在 OS X 上得到了预期的结果,但在 Android 上失败了.
Result: I got expected result on OS X, but failed on Android.
这是我的测试项目:
文件:shared.h
File: shared.h
void library_call_foo();
void __attribute__((weak)) foo();
文件:shared.c
File: shared.c
#include "shared.h"
#include <stdio.h>
void library_call_foo()
{
printf("shared library call foo -> ");
foo();
}
void foo()
{
printf("weak foo in library
");
}
文件:main.c
#include <stdio.h>
#include <shared.h>
void foo()
{
printf("strong foo in main
");
}
int main()
{
library_call_foo();
printf("main call foo -> ");
foo();
return 0;
}
我编译 &在 OS X 中使用命令运行它:
I compile & run it in OS X use commands:
clang -shared -fPIC -o libshared.so shared.c
clang -I. -L. -lshared -o test main.c
./test
按预期返回结果:
shared library call foo -> strong foo in main
main call foo -> strong foo in main
<小时>
但是当我使用 NDK 工具链为 Android 编译它时,使用相同的命令:
But when I compile it for Android with NDK toolchains use same commands:
arm-linux-androideabi-clang -shared -fPIC -o libshared.so shared.c
arm-linux-androideabi-clang -I. -L. -lshared -o test main.c
并在设备上运行它,我得到了不同的结果:
and run it on device, I got different results:
shared library call foo -> weak foo in library
main call foo -> strong foo in main
为什么行为不同,我该如何解决?
Why is the behaviors are different, and how could I fix it?
推荐答案
Android 动态链接器确实支持弱符号.问题是这个特殊情况是库是用 -Bsymbolic 编译的(检查这个运行readelf -d libshared.so").
Android dynamic linker does in fact support weak symbols. The problem is this particular case is that library is compiled with -Bsymbolic (to check this run "readelf -d libshared.so").
解决此问题的方法是在链接库时使用-Wl,-shared"而不是-shared".
The work around this is to use '-Wl,-shared' instead of '-shared' when linking the library.
请参阅 https://code.google.com/p/android/issues/detail?id=68956 了解详细信息和解决方法.
Please see https://code.google.com/p/android/issues/detail?id=68956 for details and workaround.
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