[CRIU] [PATCH 08/13] vdso: Remap runtime vdso copy to safe place

[Pavel Emelyanov]

On 05/22/2013 11:09 PM, Cyrill Gorcunov wrote:
> 
> Runtime vdso need to be kept in some safe place when all
> self-vmas are unmapped. So we reserve space for it in restorer
> blob area and then remap it into. It's quite important to do
> a remap here rather than data copy because otherwise pfn
> of vdso disappear and in future we won't be able to detect
> vdso are on dumping stage.
> 
> Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
> ---
>  cr-restore.c       | 35 ++++++++++++++++++++++++++++++++---
>  include/restorer.h |  5 +++++
>  include/vdso.h     |  2 ++
>  pie/restorer.c     | 18 ++++++++++++++++++
>  pie/vdso.c         | 17 +++++++++++++++++
>  vdso.c             |  5 +++++
>  6 files changed, 79 insertions(+), 3 deletions(-)
> 


This looks nice, but I don't see much sense in writing _plain_ wrapper
over memcpy and sys_mremap. Just call them directly.

Other than this:

> +	 * Figure out how much memory runtime vdso will need.
> +	 */
> +	vdso_copy_rt_symbols(&vdso_sym_rt);

No need in copying symbols on stack and then on arguments. Copy them on
arguments on demand.

> +	vdso_rt_size = symtable_vma_size(&vdso_sym_rt);
> +	if (vdso_rt_size)
> +		vdso_rt_delta = ALIGN(restore_bootstrap_len, PAGE_SIZE) - restore_bootstrap_len;
> +
> +	/*

> +	/*
> +	 * Where is a safe place for runtime vdso being kept
> +	 * (non intersecting with anything else) since we need
> +	 * it being accessible even when own self-vmas are unmaped.
> +	 */
> +	vdso_rt_parked_at  = exec_mem_hint + restore_bootstrap_len;
> +	vdso_rt_parked_at += vdso_rt_delta;
>  

Plz, follow existing way of filling the bootstrap area.

mem += prev_area_size;
next_area = mem
bla_bla_bla;

mem += next_area_size
next2_area = mem
bla_bla_bla2

mem += next2_area_size
bla_bla_bla3