[Ffmpeg-devel] [BUG] Compilation failure when using --disable-opts

[Roman Shaposhnik]

Hi

On Thu, 2007-03-15 at 03:52 +0100, Michael Niedermayer wrote:
> Hi
> 
> On Thu, Mar 15, 2007 at 01:32:50AM +0000, M?ns Rullg?rd wrote:
> > Michael Niedermayer <michaelni at gmx.at> writes:
> > 
> > > Hi
> > >
> > > On Thu, Mar 15, 2007 at 12:44:03AM +0000, M?ns Rullg?rd wrote:
> > >> Michael Niedermayer <michaelni at gmx.at> writes:
> > >> 
> > >> > Hi
> > >> >
> > >> > On Thu, Mar 15, 2007 at 12:13:07AM +0000, M?ns Rullg?rd wrote:
> > >> >> Michael Niedermayer <michaelni at gmx.at> writes:
> > >> >> 
> > >> >> > Hi
> > >> >> >
> > >> >> > On Wed, Mar 14, 2007 at 10:16:59PM +0000, M?ns Rullg?rd wrote:
> > >> >> >> Panagiotis Issaris <takis at issaris.org> writes:
> > >> >> > [...]
> > >> >> >> >> And are you certain that this is correct for x86_64?  Is
> > >> >> >> >> the check even needed there, what with all the extra
> > >> >> >> >> registers?
> > >> >> >> > Actually, I do not really know... I figured that because
> > >> >> >> > x86_64 is backwards compatible
> > >> >> >> 
> > >> >> >> The instruction set is compatible, meaning that everything
> > >> >> >> that works on 32-bit x86 still works on a 64-bit chip.
> > >> >> >> Things that don't work on 32-bit chips might still be
> > >> >> >> possible.  8 extra registers come to mind...
> > >> >> >> 
> > >> >> >> > the registers are still there and the tests should still
> > >> >> >> > work. In the worst case the tests would be unnecessary
> > >> >> >> > ofcourse... Prefer to remove it and only add it when
> > >> >> >> > someone figures out how this works on x86_64?
> > >> >> >> 
> > >> >> >> I don't think this is very urgent, so I'd rather wait a day
> > >> >> >> for someone with the knowledge to shed some light.
> > >> >> >
> > >> >> > the tests should be run on x86_64 too
> > >> >> 
> > >> >> Care to explain? 
> > >> >
> > >> > well if the x86 code is put under a CONFIG_EBX which is never set
> > >> > for x86_64 then you practically disable it for x86_64, not nice ...
> > >> 
> > >> What I meant was, is ebx ever reserved the same way on x86_64?  
> > >
> > > i dont know what gcc does with PIC on x86-64 maybe it doesnt reserve
> > > ebx/rbx after all theres no technical reason why it reserves it on
> > > x86-32 it could just handle the extra indirection over the GOT table
> > > like any other pointer dereference in C
> > 
> > Can you suggest some test we could do to find out?
> 
> assume ebx is always available on x86-64 and wait for bugreports ...
> 
> anyway i think zuxy is right that x86-64 uses rip relative addressing to
> reach the GOT but then again thats just what should be done iam too
> tired to use google to check if it actually is ...

  http://www.x86-64.org/documentation/abi.pdf

Thanks,
Roman.

P.S. Its funny that we've had to do a bit of funny dancing on the
compiler side to accommodate weird requests from kernel folks,
but in general zuxy is absolutely right