I am trying to implement my own C++ new & delete operators in my program as below:
#include <stdio.h>
#include <stdlib.h>
#include <new>
using namespace std;
void *operator new(std::size_t size) throw(std::bad_alloc)
{
printf("My new is called!\n");
return malloc(size);
}
void operator delete(void *ptr) throw ()
{
printf("My delete is called!\n");
free(ptr);
}
void *operator new(std::size_t size, const std::nothrow_t&) throw()
{
return malloc(size);
}
void operator delete(void *ptr, const std::nothrow_t&) throw()
{
free(ptr);
}
void *operator new[](std::size_t size) throw(std::bad_alloc)
{
return malloc(size);
}
void operator delete[](void *ptr) throw ()
{
free(ptr);
}
void *operator new[](std::size_t size,
const std::nothrow_t&) throw()
{
return malloc(size);
}
void operator delete[](void *ptr,
const std::nothrow_t&) throw()
{
free(ptr);
}
class Object
{
public:
Object() {}
~Object() {}
private:
int a;
};
int main()
{
Object* obj = new Object();
if (obj)
delete obj;
return 0;
}
Then I find that, if the program is built out as:
- an exe, then my new/delete is called as expected
- a shared-object, then symbols of new & delete is to be relocated, so in my env when this so is loaded by dlopen in another program then the new & delete will be mapped to another program's new & delete.
The detailed information is as bellow.
build out an exe:
$ gcc -m32 -c main.cpp
$ gcc -m32 main.o -o main.exe
$ ./main.exe
My new is called!
My delete is called!
$ objdump -d main.exe
080484ac <main>:
80484ac: 55 push %ebp
80484ad: 89 e5 mov %esp,%ebp
80484af: 53 push %ebx
80484b0: 83 ec 24 sub $0x24,%esp
80484b3: 83 e4 f0 and $0xfffffff0,%esp
80484b6: b8 00 00 00 00 mov $0x0,%eax
80484bb: 83 c0 0f add $0xf,%eax
80484be: 83 c0 0f add $0xf,%eax
80484c1: c1 e8 04 shr $0x4,%eax
80484c4: c1 e0 04 shl $0x4,%eax
80484c7: 29 c4 sub %eax,%esp
80484c9: c7 04 24 04 00 00 00 movl $0x4,(%esp)
80484d0: e8 1f ff ff ff call 80483f4 <_Znwj>
^-> new: expected!!
80484d5: 89 c3 mov %eax,%ebx
80484d7: 89 1c 24 mov %ebx,(%esp)
80484da: e8 35 00 00 00 call 8048514 <_ZN6ObjectC1Ev>
80484df: 89 5d f8 mov %ebx,-0x8(%ebp)
80484e2: 83 7d f8 00 cmpl $0x0,-0x8(%ebp)
80484e6: 74 22 je 804850a <main+0x5e>
80484e8: 8b 45 f8 mov -0x8(%ebp),%eax
80484eb: 89 45 e8 mov %eax,-0x18(%ebp)
80484ee: 83 7d e8 00 cmpl $0x0,-0x18(%ebp)
80484f2: 74 16 je 804850a <main+0x5e>
80484f4: 8b 45 e8 mov -0x18(%ebp),%eax
80484f7: 89 04 24 mov %eax,(%esp)
80484fa: e8 1b 00 00 00 call 804851a <_ZN6ObjectD1Ev>
80484ff: 8b 45 e8 mov -0x18(%ebp),%eax
8048502: 89 04 24 mov %eax,(%esp)
8048505: e8 0a ff ff ff call 8048414 <_ZdlPv>
^-> delete: expected
build out a shared object:
$ gcc -m32 -c main.cpp
$ gcc --shared -m32 main.o -o main.so
$ objdump -d main.so
000006d4 <main>:
6d4: 55 push %ebp
6d5: 89 e5 mov %esp,%ebp
6d7: 53 push %ebx
6d8: 83 ec 24 sub $0x24,%esp
6db: 83 e4 f0 and $0xfffffff0,%esp
6de: b8 00 00 00 00 mov $0x0,%eax
6e3: 83 c0 0f add $0xf,%eax
6e6: 83 c0 0f add $0xf,%eax
6e9: c1 e8 04 shr $0x4,%eax
6ec: c1 e0 04 shl $0x4,%eax
6ef: 29 c4 sub %eax,%esp
6f1: c7 04 24 04 00 00 00 movl $0x4,(%esp)
6f8: e8 fc ff ff ff call 6f9 <main+0x25>
---> new: to be relocated, unexpected :(
6fd: 89 c3 mov %eax,%ebx
6ff: 89 1c 24 mov %ebx,(%esp)
702: e8 fc ff ff ff call 703 <main+0x2f>
707: 89 5d f8 mov %ebx,-0x8(%ebp)
70a: 83 7d f8 00 cmpl $0x0,-0x8(%ebp)
70e: 74 22 je 732 <main+0x5e>
710: 8b 45 f8 mov -0x8(%ebp),%eax
713: 89 45 e8 mov %eax,-0x18(%ebp)
716: 83 7d e8 00 cmpl $0x0,-0x18(%ebp)
71a: 74 16 je 732 <main+0x5e>
71c: 8b 45 e8 mov -0x18(%ebp),%eax
71f: 89 04 24 mov %eax,(%esp)
722: e8 fc ff ff ff call 723 <main+0x4f>
---> delete: to be relocated, unexpected :(
727: 8b 45 e8 mov -0x18(%ebp),%eax
72a: 89 04 24 mov %eax,(%esp)
72d: e8 fc ff ff ff call 72e <main+0x5a>
