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

David Laight
2020-08-03T08:27:31Z

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.

David

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