Re: gcc 7.3: Replacing global operator new/delete in shared libraries

[Jonathan Wakely <jwakely.gcc@gmail.com>]

On 7 February 2018 at 23:38, Martin Sebor wrote:
> On 02/06/2018 03:56 PM, Paul Smith wrote:
>>
>> Hi all.
>>
>> Hopefully this isn't too annoying a question :).
>>
>> My environment has been using GCC 6.2 (locally compiled) on GNU/Linux
>> systems.  We use a separate heap management library (jemalloc) rather
>> than the libc allocator.  The way we did this in the past was to
>> declare operator new/delete (all forms) as inline functions in a header
>> and ensure that this header was always the very first thing in every
>> source file, before even any standard header files.  I know that inline
>> operator new/delete isn't OK in the C++ standard, but in fact it has
>> worked for us on the systems we care about.
>
>
> I don't know if something has changed that would expose this
> problem but...
>
> I'm not sure I see how defining operator new inline can work
> unless you recompile the world (i.e., all the DSOs used by
> the program, including libstdc++). As Marc already hinted,
> if libstdc++ dynamically allocates an object using the default
> operator new and returns that object to the program to destroy,
> it will end up causing a mismatch.

And without actually checking the code, I'm pretty sure that's what
happens in this case:

#include <iostream>
int main()
{
  std::string s;
  std::cin >> s;
}

The code to read a string from an istream is instantiated in the
library, so the string gets resized (allocating using malloc) by code
inside libstdc++.so.6 and then the destructor is run (deallocating
using your inline operator delete) in main.

That would be my first guess at explaining the stack trace you showed.