GCC Bugs
Issue With std::function (and lambdas) With gcc and arm
This specific bug has caused be much pain when cross-compiling C++ code for the Zynq 7020 SoC (which has ARM A9 processors on-board). This caused software to seg fault for not good reason. It appeared when trying to use a captured this inside of a lambda function.
Code To Cause Issue:
#include <iostream>#include <functional>
class App {
public:
std::function<App*()> test_;
void Run() {
// Enable this line, ERROR is printed // Disable this line, app runs o.k. std::cout << "This print statement causes the bug below!" << std::endl;
test_ = [this] () { return this; };
App* returnedThis = test_(); if(returnedThis != this) { std::cout << "ERROR: 'this' returned from lambda (" << returnedThis << ") is NOT the same as 'this' (" << this << ") !?!?!?!?!" << std::endl; } else { std::cout << "Program run successfully." << std::endl; }
}};
int main(void) { App app; app.Run();}
The print to std::cout
causes the bug to occur. Other, non-stream operations will likely cause a similar issue
Effects: Effects GCC v6.2.0, possibly others.
Workaround: Either compile with only -O0 or -O1 level optimizations, or add the gcc compiler flag -fno-schedule-insns2 (which disables instruction scheduling).
I posted a question on StackOverflow regarding this bug. Phillip Huppertz then found the bug logged in gcc’s bugzilla.