Re: where do I figure out "relocation R_X86_64_PC32" errors

[sean <seandarcy2 at gmail dot com>]

H. J. Lu wrote:
> On Sun, Sep 17, 2006 at 09:27:29PM -0400, sean wrote:
>
> > Alan Modra wrote:
> >
> > > On Sun, Sep 17, 2006 at 05:05:14PM -0400, sean wrote:
> > >
> > >
> > > > H. J. Lu wrote:
> > > >
> > > >
> > > > > On Sun, Sep 17, 2006 at 10:38:23AM -0400, sean wrote:
> > > > >
> > > > >
> > > > > > mmx_00ffw is just a constant in yuv2rgb.c:
> > > > > >
> > > > > > uint64_t attribute_used __attribute__((aligned(8))) 
> > > > > > mmx_00ffw = 0x00ff00ff00ff00ffULL;
> > >
> > >
> > > The trouble is that this variable is used in asm statements using rip
> > > addressing, and the variable is global.  ELF shared libraries have
> > > particular rules regarding global symbol resolution;  A global symbol
> > > in a shared library may be overridden by the same symbol in the main
> > > app code (or another shared lib).  rip addressing won't work in this
> > > situation for two reasons: a) the rip offset is in read-only code, so
> > > relocating the offset means the library can't share that page of text,
> > > and more seriously, b) the rip offset is only 32-bit so might not
> > > reach to the app symbol or another library sym (64-bit address space).
> > >
> > > There is a simple fix.  Add __attribute__ ((hidden)) to the variable
> > > definition to make it local to the shared library.
> >
> > Nope. Same error message.
> >
> > grep 00ffw ffmpeg/libswscale/yuv2rgb.c
> > uint64_t attribute_used __attribute__((aligned(8))) 
> > __attribute__((hidden)) mmx_00ffw = 0x00ff00ff00ff00ffULL;
>
>
> It should be __attribute__((visibility("hidden"))).
>
>
> H.J.

Yup. That did it.

Is this a generalizable lesson. That is, if I have another 
problem with  -fPIC not allowing linking, I need to modify 
the attributes? Or is this clever thinking amongst the 
cognescenti?

In any event, thanks for all the help. I appreciate the time 
and attention.

sean