同名新二进制文件上的dlopen返回旧句柄 [英] dlopen on new binary with same name returns old handle

问题描述

我正在使用dlopen加载动态生成的代码.该程序在代码上调用编译器，并生成一个.so文件，然后由该程序加载以扩展自身.

I'm using dlopen to load dynamically generated code. The program calls the compiler on the code and generates a .so file which is then loaded by the program to extend itself.

问题是，如果我对生成的代码使用相同的名称，则dlopen将返回旧对象的句柄，而不是新对象的句柄.

The problem is that if I use the same name for the generated code, the dlopen returns a handle to the old object, not the new one.

代码如下:

…generate code into test.cpp
system("gcc <args> test.cpp -o test.so");
void *handle = dlopen("test.so");
void *sym = dlsym(handle, "run");
(*sym)();
dlclose(handle);
…Do other work
…generate different code to test.cpp
system("gcc <args> test.cpp -o test.so");
void *handle = dlopen("test.so");
void *sym = dlsym(handle, "run");
(*sym)();
<crash here because the code isn't what was expected>

这是否是 dlopen 的缓存代码中的基本缺陷，还是 dlopen 中没有很好记录的东西?

Is this a basic flaw in dlopen's cache code or something well known and not well documented in dlopen?

推荐答案

大多数可能 dlclose 无法卸载该库.这通常发生在它包含 GNU_UNIQUE符号(如果您与静态libstdc ++链接).可以通过

Most probly dlclose failed to unload the library. This usually happens when it contains GNU_UNIQUE symbols (which tend to sneak in if you link with static libstdc++). This can be verified via

$ readelf -sW --dyn-syms path/to/libxyz.so | grep '\bUNIQUE\b'
...
3808: 0000000000302e78     8 OBJECT  UNIQUE DEFAULT   27 _ZNSt8messagesIcE2idE@@GLIBCXX_3.4

要解决此问题，您可以尝试以下操作之一:

To fix this, you can try one of the following:

• 使用 -fvisibility = hidden 和 __ attribute __((visibility("default")))构建库以隐藏唯一的符号
• 使用 -Wl，-version-script 构建以实现相同的目的
• 使用通过-disable-gnu-unique-object 配置的工具链构建shlib(请参阅

• build library with -fvisibility=hidden and __attribute__((visibility("default"))) to hide unique symbols
• build with -Wl,--version-script to achieve the same
• build shlib with toolchain that was configured with --disable-gnu-unique-object (see discussion in GCC list)

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