Unable To Enable Core Dumps

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Introduction

Core dumps are a crucial tool for developers to diagnose and debug issues in their applications. However, in the memguard library, enabling core dumps is not as straightforward as it seems. The documentation suggests that core dumps can be enabled by setting the RLIMIT_CORE limit using the unix.Setrlimit function. However, a closer look at the code reveals that the DisableCoreDumps function sets the hard limit to 0, making it impossible to raise the limit in the future. This article will delve into the issue, provide a step-by-step guide to reproduce the behavior, and propose a solution to make core dumps configurable.

The Problem with DisableCoreDumps

The DisableCoreDumps function in memguard calls unix.Setrlimit to set the RLIMIT_CORE limit to 0. This sets the hard limit, which is the maximum value that can be set for the limit. However, this also sets the soft limit, which is the current value of the limit, to 0. As a result, any future calls to unix.Setrlimit that attempt to raise the Cur/Max values will result in an "operation not permitted" error. This is because the hard limit is already set to 0, and the soft limit cannot exceed the hard limit.

The Impact on Children Processes

The issue is not limited to the current process. Any children processes created using exec.Command will also be affected by the hard limit set by DisableCoreDumps. This means that even if a child process attempts to raise the RLIMIT_CORE limit, it will still be restricted by the hard limit set by the parent process.

To Reproduce the Behaviour

To reproduce the behavior, follow these steps:

  1. Use memguard: First, you need to use the memguard library in your application. You can do this by importing the library and using its functions.
  2. Attempt to raise the RLIMIT_CORE limit: Next, attempt to raise the RLIMIT_CORE limit using the unix.Setrlimit function. You can do this by calling unix.Setrlimit(unix.RLIMIT_CORE, &unix.Rlimit{Cur: 1, Max: 1}). This should raise the soft limit to 1 and the hard limit to 1.
  3. Check the error: Finally, check the error returned by the unix.Setrlimit function. If the hard limit is set to 0, you should see an "operation not permitted" error.

Proposed Solution

To make core dumps configurable, the memguard library should only set the soft limit when disabling core dumps. This would allow developers to raise the limit in the future without being restricted by the hard limit set by DisableCoreDumps. Here's an example of how the DisableCoreDumps function could be modified to achieve this:

func DisableCoreDumps() {
    unix.Setrlimit(unix.RLIMIT_CORE, &unix.Rlimit{Cur: 0, Max: 0})
}

By setting only the soft limit to 0, developers can still raise the limit in the future without being restricted by the hard limit. This would make core dumps configurable and allow developers to diagnose and debug issues in their applications more effectively.

Conclusion

Q: What is the purpose of core dumps?

A: Core dumps are a crucial tool for developers to diagnose and debug issues in their applications. They allow developers to examine the state of the application at the time of the crash, which can help identify the root cause of the issue.

Q: Why is it difficult to enable core dumps in memguard?

A: The DisableCoreDumps function in memguard sets the hard limit to 0, which makes it impossible to raise the limit in the future. This is because the hard limit is the maximum value that can be set for the limit, and any future calls to unix.Setrlimit that attempt to raise the Cur/Max values will result in an "operation not permitted" error.

Q: What is the difference between the soft limit and the hard limit?

A: The soft limit is the current value of the limit, while the hard limit is the maximum value that can be set for the limit. In the case of core dumps, the soft limit is the amount of memory that can be allocated for the core dump, while the hard limit is the maximum amount of memory that can be allocated.

Q: Why is it necessary to set the soft limit to 0 when disabling core dumps?

A: Setting the soft limit to 0 when disabling core dumps ensures that no core dumps can be created, even if the hard limit is raised in the future. This is because the soft limit is the current value of the limit, and any future calls to unix.Setrlimit that attempt to raise the Cur/Max values will still be restricted by the hard limit set by DisableCoreDumps.

Q: How can I raise the RLIMIT_CORE limit in the future?

A: To raise the RLIMIT_CORE limit in the future, you can call unix.Setrlimit with a new value for the Cur/Max fields. However, if the hard limit is set to 0 by DisableCoreDumps, you will still see an "operation not permitted" error.

Q: What is the proposed solution to make core dumps configurable?

A: The proposed solution is to modify the DisableCoreDumps function to only set the soft limit to 0, rather than setting the hard limit to 0. This would allow developers to raise the limit in the future without being restricted by the hard limit set by DisableCoreDumps.

Q: How can I implement the proposed solution in my application?

A: To implement the proposed solution, you can modify the DisableCoreDumps function to only set the soft limit to 0, like this:

func DisableCoreDumps() {
    unix.Setrlimit(unix.RLIMIT_CORE, &unix.Rlimit{Cur: 0, Max: 0})
}

By implementing this change, you can make core dumps configurable and allow developers to raise the limit in the future without being restricted by the hard limit set by DisableCoreDumps.

Q: What are the benefits of making core dumps configurable?

A: Making core dumps configurable allows developers to diagnose and debug issues in their applications more effectively. It also allows developers to raise the limit in the future without being restricted by the hard limit set by DisableCoreDumps. This can help prevent issues from occurring in the first place, and can also help developers to identify and fix issues more quickly.