Скачать или смотреть How to Set the Stack Size for a Shared Library in GCC?

Discover why you can't set the stack size of a shared library in GCC and learn about the implications for your code.
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Understanding Stack Size in Shared Libraries

When working with shared libraries in C or C+ + , developers occasionally run into issues relating to memory usage, particularly when large local variables are concerned. A common question is whether it's possible to explicitly set the stack size of a shared library function when using GCC. Let's delve into this problem and clarify how you can manage stack sizes in the context of shared libraries.

The Problem at Hand

Imagine you have created a shared library (.so file) that contains a function using a massive locally scoped array. For example:

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You might think that using the GCC option -Wl,-z,stack-size=4100000 would allow you to define a larger stack size for this. However, you notice that this setting doesn't seem to work when specified for a "shared library". This raises the question: Is it possible to set the stack size for a shared library function?

The Answer: No, It’s Not Possible

Unfortunately, the short answer is no. Here’s why:

Thread Context Matters

Function Calls: When a function from a shared library is called, it runs in the context of the thread that invoked it. This means one of two scenarios occurs:

The call comes from the main application thread, which is created in the main function.

The call is made from a thread generated via the POSIX threads (Pthreads) model.

Stack Allocation: The stack space for each thread is allocated at the time of thread creation, specifically in the pthread_create function. Therefore, any stack size settings applied at the shared library level do not influence the calling thread's stack size.

The -Wl,-z,stack-size Flag Misunderstanding

Applicability: The flag -Wl,-z,stack-size is only applicable to applications, not libraries. When you set it, you’re defining the stack size for the main thread of the application, not for any threads created via shared libraries. Thus, attempting to enforce a larger stack size within a shared library context is futile.

Practical Solutions

Since modifying the stack size directly in shared libraries isn’t possible, what can you do if you expect functions that use large amounts of stack memory?

Alternative Strategies

Use Dynamic Memory Allocation: Instead of declaring large arrays on the stack, consider allocating memory dynamically using malloc or similar functions. This moves the memory allocation to the heap and circumvents stack size limitations entirely.

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Adjust Thread Stack Size: If you control the threads that call the shared library function, you can specify a larger stack size when creating those threads with pthread_create.

Optimize Memory Use: Analyze your code to check if the array size can be reduced or if you can make use of static or global variables instead.

Conclusion

Managing stack size in shared libraries is challenging because of the context in which shared library functions operate. The inability to set this size directly means developers need to depend on alternative strategies for handling large data structures. By opting for heap allocation or optimizing the overall memory usage, you can ensure your library operates smoothly without running into stack overflow issues.