Magic numbers when debugging with gcc/g++/gdb/valgrind?

Question

Microsoft's Visual C++ fills memory with 'magic numbers' if it hasn't been initialized by the programmer itself. This helps with debugging of uninitialized memory. (In Visual Studio C++, what are the memory allocation representations?, 0xDEADBEEF vs. NULL)

Is there a similar function when using linux GNU tools (g++/gdb)?

Thanks!

Answer 1

You can override the C++ operator new to set allocations to your preferred byte pattern:

void* operator new(size_t size)
{
    void* mem = malloc(size);
    if (!mem) {
        throw std::bad_alloc();
    }
    memset(mem, 0xEE, size);
    return mem;
}

You can see the full GCC implementation here: https://github.com/gcc-mirror/gcc/blob/master/libstdc%2B%2B-v3/libsupc%2B%2B/new_op.cc in case you want to mirror it more closely.

That will work for anything using the default C++ allocators, but not for things using regular old malloc(). If you need to initialize memory from malloc() directly, you can override that too, but the mechanism to do it is different: you can use the linker's --wrap option to manipulate the symbol table and let you override malloc(). Then you don't need to overload operator new of course. The full approach is illustrated in an answer here: https://stackoverflow.com/a/3662951/4323