From: Madhavan T. Venkataraman > Sent: 03 August 2020 17:03 > > 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. I said i386 not amd64 or x86-64. So yes, 64bit code has PC-relative addressing. But I'm pretty sure it has no other way to get the PC itself except using call - certainly nothing in the 'usual' instructions. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
