C++ operator delete override not always used - c++

Question

I have some C++ unit tests using google test. Threw together some code to override the new/delete operators to check for leaks in the unit tests. Having an issue though. Some of the google test new/deletes use my overridden methods, but some don't, so I get false errors in the tracking code -- sometimes seeing that memory was leaked even though it was really deleted and sometimes seeing that malloc returns
Here is my minimal new/delete overrides (just prints the addresses for manual inspection):
void * operator new(size_t size)
{
void * addr = malloc(size);
std::cout << " tracking create: " << addr << "(size " << size << ")" << std::endl;
return addr;
}
void * operator new[](size_t size)
{
void * addr = malloc(size);
std::cout << " tracking create: " << addr << "(size " << size << ")" << std::endl;
return addr;
}
void operator delete(void * addr) noexcept
{
std::cout << " tracking delete: " << addr << std::endl;
free(addr);
}
void operator delete[](void * addr) noexcept
{
std::cout << " tracking delete: " << addr << std::endl;
free(addr);
}
And here is the google test line that does NOT go through my overridden delete (gtest-port.h):
void reset(T* p = NULL) {
if (p != ptr_) {
if (IsTrue(sizeof(T) > 0)) { // Makes sure T is a complete type.
delete ptr_;
}
ptr_ = p;
}
}
When I break on the delete ptr_ line in gdb, then step, it steps directly to the ptr_ = p line, so there isn't something else overriding that delete.
I'm building gtest as an archive file and linking it in when I build my unit tests. In case it matters: I'm on windows building with mingw using cygwin.
Here's a minimal example, 2 files min.cpp and minmain.cpp. Here's min.cpp:
#include <iostream>
#include <string>
// Overload the new/delete operators to check for memory errors
void * operator new(size_t size)
{
void * addr = malloc(size);
std::cout << " tracking create: " << addr << "(size " << size << ")" << std::endl;
return addr;
}
void * operator new[](size_t size)
{
void * addr = malloc(size);
std::cout << " tracking create: " << addr << "(size " << size << ")" << std::endl;
return addr;
}
void operator delete(void * addr) noexcept
{
std::cout << " tracking delete: " << addr << std::endl;
free(addr);
}
void operator delete[](void * addr) noexcept
{
std::cout << " tracking delete: " << addr << std::endl;
free(addr);
}
minmain.cpp:
#include "gtest/gtest.h"
TEST(MinTest, MinimalTest)
{
int test = 5;
test++;
test++;
test++;
ASSERT_EQ(test, 8);
}
int main(int argc, char *argv[])
{
char* t = new char();
t[0] = 't'; std::cout << "t is " << t[0] << std::endl;
::testing::InitGoogleTest(&argc, argv);
return RUN_ALL_TESTS();
}
compiled with:
/bin/x86_64-w64-mingw32-g++.exe -std=c++11 -D_USE_MATH_DEFINES -g -Wall -I../third_party/googletest-1.8.0/googletest/include -c min.cpp -o min.o
to create the min.o, then compile main and link all together with:
/bin/x86_64-w64-mingw32-g++.exe -std=c++11 -D_USE_MATH_DEFINES -g -Wall -I../third_party/googletest-1.8.0/googletest/include -o minmain minmain.cpp min.o ../third_party/googletest-1.8.0/googletest/make/gtest_main.a
Using version 1.8.0 of gtest, break at gtest-port.h:1145 to get to the delete ptr_ line, then step.
Here is some sample output from running the example above (first few lines of output):
tracking create: 0x30e4c0(size 392)
tracking create: 0xa477e0(size 392)
tracking create: 0xa477e0(size 392)
tracking create: 0xa477e0(size 392)
tracking create: 0xa477e0(size 392)
tracking create: 0xa47b80(size 28)
tracking delete: 0xa47b80
The fact that I get tracked creates on the same address with no tracked deletes in between is a problem, because there were deletes in between allowing the same address to be allocated again, but those deletes did not go through my overridden delete operator.
Why does that delete ptr_; line in gtest not use my overridden delete function?

Answer 1

Looks like this is a bug in MinGW:
MinGW bug #634
A work-around is to link the static version of libstdc++ instead of letting it link the dynamic library. Not the most ideal solution, but it's good enough for my unit tests and it allows me to override correctly.
I modified by compile/link command to the following to do this:
/bin/x86_64-w64-mingw32-g++.exe -std=c++11 -D_USE_MATH_DEFINES -g -Wall -I../third_party/googletest-1.8.0/googletest/include -o minmain minmain.cpp min.o ../third_party/googletest-1.8.0/googletest/make/gtest_main.a /cygdrive/c/cygwin64/lib/gcc/x86_64-w64-mingw32/6.4.0/libstdc++.a
Mucho thanko to Peter for putting me down the right path to finding this.