Using assembly JMP function on x86_64

Question

I'm really new to programming (in general - it's pathetic) and some Python-related assembly has cropped up in this app that I'm hacking to run on 64-bit.

Essentially, the code goes like this:

#define FUNCTION(name)        \
  .globl _##name;             \
  _##name:                    \
    jmp *(_p_##name)

.text
  FUNCTION(name)

The FUNCTION(name) syntax is used about 50 times to define headers for an external Python library as far as I can tell (I'm not going to pretend that I fully understand it, I'm just bugfixing).

Since I'm compiling for x86_64, the following error is spit out by GCC for each FUNCTION(name) instance:

32-bit absolute addressing is not supported for x86-64

cannot do signed 4 byte relocation

How would I go about "fixing" this to run on x86_64?

Answer 1

Grab a copy of the Intel Architecture Software Developer's Manuals. As you're seeing, some forms of the jmp instruction are invalid in 64-bit mode. In particular, the two "Jump far, absolute, address given in operand" forms won't work. You will need to change to a relative addressing or absolute indirect addressing form of the instruction. Volume 2A, page 3-549 in my copy, of the manual has a huge pile of information about jmp.