Where is __dso_handle defined?

问题

I have an unresolved symbol error when trying to compile my program which complains that it cannot find __dso_handle. Which library is this function usually defined in?

Does the following result from nm on libstdc++.so.6 mean it contains that?

I tried to link against it but the error still occurs.

nm libstdc++.so.6 | grep dso
00000000002fc480 d __dso_handle

回答1:

__dso_handle is a "guard" that is used to identify dynamic shared objects during global destruction.

Realistically, you should stop reading here. If you're trying to defeat object identification by messing with __dso_handle, something is likely very wrong.

However, since you asked where it is defined: the answer is complex. To surface the location of its definition (for GCC), use iostream in a C++ file, and, after that, do extern int __dso_handle;. That should surface the location of the declaration due to a type conflict (see this forum thread for a source).

Sometimes, it is defined manually.

Sometimes, it is defined/supplied by the "runtime" installed by the compiler (in practice, the CRT is usually just a bunch of binary header/entry-point-management code, and some exit guards/handlers). In GCC (not sure if other compilers support this; if so, it'll be in their sources):

Main definition
Testing __dso_handle replacement/tracker example 1
Testing __dso_handle replacement/tracker example 2

Often, it is defined in the stdlib:

Android
BSD

回答2:

I ran into this problem. Here are the conditions which seem to reliably generate the trouble:

g++ linking without the C/C++ standard library: -nostdlib (typical small embedded scenario).
Defining a statically allocated standard library object; specific to my case is std::vector. Previously this was std::array statically allocated without any problems. Apparently not all std:: statically allocated objects will cause the problem.
Note that I am not using a shared library of any type.
GCC/ARM cross compiler is in use.

If this is your use case then merely add the command line option to your compile/link command line: -fno-use-cxa-atexit

Here is a very good link to the __dso_handle usage as 'handle to dynamic shared object'.

There appears to be a typo in the page, but I have no idea who to contact to confirm:

~~After you have called the objects' constructor destructors GCC automatically calls the function ...~~

I think this should read "Once all destructors have been called GCC calls the function" ...

One way to confirm this would be to implement the __cxa_atexit function as mentioned and then single step the program and see where it gets called. I'll try that one of these days, but not right now.

来源：https://stackoverflow.com/questions/34308720/where-is-dso-handle-defined

标签

linker

llvm

libstdc++