Re: [PATCH 3/12] i386: Force section size to be non-zero to prevent a symbol becoming absolute

Vivek Goyal
2006-10-04T16:14:50Z

On Wed, Oct 04, 2006 at 09:09:46AM -0700, Andrew Morton wrote:
> On Tue, 3 Oct 2006 13:09:08 -0400
> Vivek Goyal <vgoyal@in.ibm.com> wrote:
>
> > o Relocation patches for i386, moved the symbols in vmlinux.lds.S inside
> > sections so that these symbols become section relative and are no more
> > absolute. If these symbols become absolute, its bad as they are not
> > relocated if kernel is not loaded at the address it has been compiled
> > for.
> >
> > o Ironically, just moving the symbols inside the section does not
> > gurantee that symbols inside will not become absolute. Recent
> > versions of linkers, do some optimization, and if section size is
> > zero, it gets rid of the section and makes any defined symbol as absolute.
> >
> > o This leads to a failure while second kernel is booting.
> > arch/i386/alternative.c frees any pages present between __smp_alt_begin
> > and __smp_alt_end. In my case size of section .smp_altinstructions is
> > zero and symbol __smpt_alt_begin becomes absolute and is not relocated
> > and system crashes while it is trying to free the memory starting
> > from __smp_alt_begin.
> >
> > o This issue is being fixed by the linker guys and they are making sure
> > that linker does not get rid of an empty section if there is any
> > section relative symbol defined in it. But we need to fix it at
> > kernel level too so that people using the linker version without fix,
> > are not affected.
> >
> > o One of the possible solutions is that force the section size to be
> > non zero to make sure these symbols don't become absolute. This
> > patch implements that.
>
> Would it be reasonable to omit this patch and require that the small number
> of people who want to build relocatable kernels install binutils
> 2.17.50.0.5 or later?

I think that's a reasonable thing to do for now.

Thanks
Vivek