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MrPlow writes:

Submitted via IRC for TheMightyBuzzard to let us know that a serious bug in GCC.

This post is to inform you about a bug in GCC that may cause memory (or other resource) leaks in your valid C++ programs.

One of the pillars of C++ philosophy is what we often call RAII [Resource Acquisition Is Initialization]: if you use classes to manage resources, use constructors for allocating resources and destructors for releasing them, the language makes sure that whatever happens, however you use such classes the resources will get properly released.

[...] This is the contract: I take care that my classes correctly manage resources, and the language takes care that the resources will always be managed correctly regardless of the complexity of the program.

This is where the bug manifests. Member r1 is initialized but never destroyed. Admittedly, this is a rare case: it requires an exception in the middle of initialization, a temporary and an aggregate initialization. But usually, leaks manifest in the face of exceptions. And the fact that it is rare makes you less prepared for it.

Here is a full example:

*SPOILER* (click to show) *SPOILER* (click to hide)

#include <cstdio>
#include <stdexcept>

struct Resource
{
  explicit Resource(int) { std::puts("create"); }
  Resource(Resource const&) { std::puts("create"); }
  ~Resource() { std::puts("destroy"); }
};

Resource make_1() { return Resource(1); }
Resource make_2() { throw std::runtime_error("failed"); }

struct User
{
  Resource r1;
  Resource r2;
};

void process (User) {}

int main()
{
  try {
    process({make_1(), make_2()});
  }
  catch (...) {}
}

You can test it online here. It is present in GCC 4, 5, and 6. For a more real-life, and somewhat longer, illustration of the problem, see this example provided by Tomasz Kamiński.

Interesting but thankfully not my worry at the moment as I'm on a Learn Rust kick and my problem areas of SN are all perl.

Source: https://akrzemi1.wordpress.com/2017/04/27/a-serious-bug-in-gcc/

Original Submission