Is there some version of longjmp that can output long values?

Question

I'm working on a framework on C language, for it I want to implement exceptions, for it I'm using longjump with setjump, but on x64 machines longjump still outputs an integer.

I've created a class (struct with vptr essentially), which represents exception, but to throw it out in code I need to throw a pointer to this structure. The pointer has an unsigned long long value (qword) for x64 machines and unsigned int (dword) for x86, so I shall require only qword to be in output to handle the error.

Are there implementations of longjmp and setjmp, which can output qword?

Or maybe I could write my own longjump, but for it the original source code is required.

Answer 1

You can enclose your jmp_buf-typed variable in a larger structure, possibly larger by just sizeof(void*). Then just before calling longjmp() you can store the pointer in that extra space. There's no need to try to squeeze a pointer into an int.

Example:

#include <stdio.h>
#include <setjmp.h>

struct jmp_buf_struct
{
  jmp_buf jb;
  void* exc_ptr;
};

void may_throw(jmp_buf jb)
{
  struct jmp_buf_struct* jbs_ptr = (struct jmp_buf_struct*)jb;
  jbs_ptr->exc_ptr = "Exception message!";
  longjmp(jb, 1);
}

int main()
{
  struct jmp_buf_struct jbs;
  if (setjmp(jbs.jb))
  {
    printf("Threw %p = \"%s\".", jbs.exc_ptr, (char*)jbs.exc_ptr);
  }
  else
  {
    may_throw(jbs.jb);
    puts("Didn't throw.");
  }
  return 0;
}

Output:

Threw 0x55638ebc78c4 = "Exception message!".