Re: [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor

Madhavan T. Venkataraman
2020-08-03T16:03:51Z

On 8/3/20 3:27 AM, David Laight wrote:
> From: Mark Rutland
>> Sent: 31 July 2020 19:32
> ...
>>> It requires PC-relative data references. I have not worked on all architectures.
>>> So, I need to study this. But do all ISAs support PC-relative data references?
>> Not all do, but pretty much any recent ISA will as it's a practical
>> necessity for fast position-independent code.
> i386 has neither PC-relative addressing nor moves from %pc.
> The cpu architecture knows that the sequence:
> call 1f
> 1: pop %reg
> is used to get the %pc value so is treated specially so that
> it doesn't 'trash' the return stack.
>
> So PIC code isn't too bad, but you have to use the correct
> sequence.

Is that true only for 32-bit systems only? I thought RIP-relative addressing was
introduced in 64-bit mode. Please confirm.

Madhavan