*When* does a C++ exception blow up C code

Ok, so I need -fexceptions to allow a C++ exception to propagate through C code. I tried to compare the results from both C++ and C, and, from what I can tell, the compiled routines are identical at the assembly, even without that option [1]. Here is the test:

#include <unistd.h>

typedef int (*Callback)(void* param,void* buffer,int n);

void write_wrapper(int fd,const void* buffer,int n)
{
    const char* temp=(const char*)buffer;
    while(n!=0)
        {
        int k=write(fd,temp,n);
        n-=k;
        temp+=k;
        }
}

int test(Callback cb,void* cb_param)
{
    char buffer[1024];
    int n=0;
    do
        {
        n=cb(cb_param,buffer,1024);
        write_wrapper(STDOUT_FILENO,buffer,n);
        }
    while(n!=1024);
}

int test2(Callback cb,void* cb_param)
{
char more_stack_space_please[1024]={0};
cb(cb_param,more_stack_space_please,1024);
write_wrapper(STDOUT_FILENO,more_stack_space_please,1024);
test(cb,cb_param);
}

Here, it is up to the caller to free resources, so there should be no leak even though the callback function throws an exception.

Even though this example appears to work (tested with simple C++ driver)

#include "lib.h"
#include <cstdio>

class Resource
    {
    public:
        Resource()
            {fprintf(stderr,"A Resource\n");}

        ~Resource()
            {fprintf(stderr,"Not a Resource\n");}
    };

int main()
    {
    try
        {
        Resource foo;
        test([](void* cb_param,void* buffer, int n)->int
            {
            Resource bar;
            throw "test";
            },nullptr);
        test2([](void* cb_param,void* buffer, int n)->int
            {
            throw "test2";
            },nullptr);
        }
    catch(const char* err)
        {
        fprintf(stderr,"Error: %s\n",err);
        return -1;
        }
    return 0;
    }

, I have got uncaught exception errors from GTK callbacks. My thoughts:

• GTK is a shared library, so maybe it only affects the linker, and not the code generator
• GTK (and GLib) contains a lot strange hacks, that may screw things up

[1] https://godbolt.org/g/HfSnjB