What are the differences comparing PIE, PIC code and executable on 64-bit x86 platform?

Question

The test is on Ubuntu 12.04 64-bit. x86 architecture.

I am confused about the concept Position Independent Executable (PIE) and Position Independent code (PIC), and

Answer 1

I am confused about the concept Position Independent Executable (PIE) and Position Independent code (PIC), and I guess they are not orthogonal.

The only real difference between PIE and PIC is that you are allowed to interpose symbols in PIC, but not in PIE. Except for that, they are pretty much equivalent.

You can read about symbol interposition here.

C. a_pie.out contains syntax-identical instructions comparing with a_pic.out. However, the memory addresses of a_pie.out's .text section range from 0x630 to 0xa57, while the same section of a_pic.out ranges from 0x400410 to 0x400817.

It's hard to understand what you find surprising about this.

The PIE binary is linked just as a shared library, and so its default load address (the .p_vaddr of the first LOAD segment) is zero. The expectation is that something will relocate this binary away from zero page, and load it at some random address.

On the other hand, a non-PIE executable is always loaded at its linked-at address. On Linux, the default address for x86_64 binaries is 0x400000, and so the .text ends up not far from there.