[U-Boot] armv8 relocation questions

[Wolfgang Denk]

Dear Jeroen,

In message <1400485047.1998.17.camel at yellow> you wrote:
> 
> > > "ADRP Xd, label
> > ...
> > > And apparently gcc choose to use it as such. Since the instructions in
> > 
> > Where exactly does it chose to do so?
> 
> In the code emitter which decide to use the following instructions to
> look up a label, as mentioned by David [1]. Since it only uses _part of_
> the pc, it introduces the need to have the relocation offset be a
> multiple of 4k.  
> 
>      adrp  x0,  ...
>      add   x0, x0, 0x30

No.  I mean: to which exact lines of U-Boot C source code will be
translated into that?

I mean, from what has been discussed here that would be the relocation
loop, right?  And there this should not happen, as we deal with random
addresses.  So I wonder if this is either a coding error in the armv8
related assembler code, or a compiler bug, or something else?

> >  I cannot understand why that
> > should be a problem for _start, but not for any of the other symbols
> > we're relocating?
> 
> It is not a problem of _start. Any label / symbol which is looked up
> with only the adrp + compile time offset will be incorrect if the
> relocation offset is not n * 4k. It just that moving _start around makes
> the relocation offset not obey this requirement.

Well, in this case relocation can never work correctly, so we're back
at my question above: bad assembly code of the armv8 port, or a
compiler bug?

> > Sorry, I cannot follow.  where exactly does this happen, and why
> > there, and not anywhere else?
> 
> In any code emitted which uses above pattern. And above code works fine
> if text is 4k natural aligned before and after relocation. It also works
> fine when the same offset is used before and after relocation.

The question is - where does such code get emitted?  Is it generated
from C code, or manually created assembly?

I would like to see the exact source code reference into U-Boot
code...

Best regards,

Wolfgang Denk

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