Re: [PATCH] powerpc/boot: request no dynamic linker for boot wrapper

[Nicholas Piggin <npiggin@gmail.com>]

On Mon, 28 Nov 2016 12:39:38 +0000
Nick Clifton <nickc@redhat.com> wrote:

> Hi Nicholas,
> 
> >>> The boot wrapper performs its own relocations and does not require
> >>> PT_INTERP segment.
> >>>
> >>> Without this option, binutils 2.28 and newer tries to create a program
> >>> header segment due to PT_INTERP, and the link fails because there is no
> >>> space for it.    
> >>
> >> 2.28 is not released yet though is it?
> >>
> >> So can we just declare versions with that behaviour broken?  
> > 
> > No it's not released yet, but I don't know if it's due entirely to binutils
> > bug. Let's see what Nick thinks.  
> 
> Well the patch that caused this problem was an attempt to fix the linker so 
> that it would enforce the ELF standard.  Prior to the patch the linker would 
> silently create binaries that violated the standard and which, at least for
> the people reporting the problem in binutils PR 20815, failed to execute.
> 
> It now appears however that some programs, including the boot wrapper and the
> Linux kernel, may actually rely upon non-standard ELF binaries being created.
> Before I revert the patch however, I would like to ask...
> 
> >>> +# Do not include PT_INTERP segment when linking pie. Non-pie linking
> >>> +# just ignores this option.
> >>> +LD_VERSION=$(${CROSS}ld --version | $srctree/scripts/ld-version.sh)
> >>> +LD_NO_DL_MIN_VERSION=$(echo 2.26 | $srctree/scripts/ld-version.sh)
> >>> +if [ "$LD_VERSION" -ge "$LD_NO_DL_MIN_VERSION" ] ; then
> >>> +	nodl="--no-dynamic-linker"
> >>> +fi    
> 
> ... this actually seems like a better fix to me.  If you do not want the 
> PT_INTERP segment, then telling this linker this is a good idea.  So wouldn't
> a patch like this be a better solution to the problem ?

Yes, I wasn't asking for the binutils change to be reverted. We're
generally happy to adapt to toolchain improvements. I don't think the
boot wrapper is relying on this non-standard form. If we go with
--no-dynamic-linker then I'm assuming we get a standard ELF binary?
That seems desirable.

I was just checking whether this is the best think for the kernel to do.
Is it possible to get a similar behaviour using the linker script instead
(so it's compatible with older binutils)?

Thanks,
Nick