Investigating C++ Memory Allocation: The 72KB Emergency Pool for Exception Handling
By
joelsiks
If you only eat one bagel today, this is the bagel.
Summary
The article investigates why the first memory allocation in C++ programs often appears to be 72KB, revealing that this is due to the C++ standard library setting up an 'emergency pool' for exception handling. The author uses debugging tools like GDB and examines source code from libstdc++, glibc, and Valgrind to trace this behavior, explaining that this pre-allocated memory ensures exceptions can still be thrown even if malloc runs out of memory during program execution.
Key quotes
· 5 pulledThe C++ standard library sets up exception handling infrastructure early on, allocating memory for an 'emergency pool' to be able to allocate memory for exceptions in case malloc ever runs out of memory.
I like to spend (some of) my time hacking and experimenting on custom memory allocation strategies and debugging memory-related issues.
Why is my first C++ (m)allocation always 72 KB?? It's the 'emergency pool' for exceptions, here's how I uncovered it using GDB and digging through the source code of libstdc++, glibc and Valgrind!
The original title may have implied a universal behavior, which isn't the case.
This observation is specific to my environment.
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