[U-Boot] [PATCH v2 1/4] mx31pdk: copy SPL directly, not using relocate_code.

[Albert ARIBAUD]

Hi Benoît,

On Tue, 14 May 2013 19:10:10 +0200 (CEST), Benoît Thébaudeau
<benoit.thebaudeau at advansee.com> wrote:

> Hi Albert,
> 
> On Tuesday, May 14, 2013 6:13:55 PM, Albert ARIBAUD wrote:
> > Hi Benoît,
> > 
> > On Tue, 14 May 2013 17:14:12 +0200 (CEST), Benoît Thébaudeau
> > <benoit.thebaudeau at advansee.com> wrote:
> > 
> > > Hi Albert,
> > > 
> > > On Tuesday, May 14, 2013 11:50:27 AM, Albert ARIBAUD wrote:
> > > > Signed-off-by: Albert ARIBAUD <albert.u.boot at aribaud.net>
> > > > ---
> > > > Changes in v2:
> > > > - dropped relocate_code() call from mx31pdk SPL
> > > > 
> > > >  board/freescale/mx31pdk/mx31pdk.c |   16 +++++++++++++++-
> > > >  1 file changed, 15 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/board/freescale/mx31pdk/mx31pdk.c
> > > > b/board/freescale/mx31pdk/mx31pdk.c
> > > > index 49158bd..4f6cfee 100644
> > > > --- a/board/freescale/mx31pdk/mx31pdk.c
> > > > +++ b/board/freescale/mx31pdk/mx31pdk.c
> > > > @@ -39,7 +39,21 @@ DECLARE_GLOBAL_DATA_PTR;
> > > >  #ifdef CONFIG_SPL_BUILD
> > > >  void board_init_f(ulong bootflag)
> > > >  {
> > > > -	relocate_code(CONFIG_SPL_TEXT_BASE);
> > > > +	/*
> > > > +	 * copy ourselves from where we are running to where we were
> > > > +	 * linked at. Use ulong pointers as all addresses involved
> > > > +	 * are 4-byte-aligned.
> > > > +	 */
> > > > +	ulong *start_ptr, *end_ptr, *link_ptr, *run_ptr, *dst;
> > > > +	asm volatile ("ldr %0, =_start" : "=r"(start_ptr));
> > > > +	asm volatile ("ldr %0, =_end" : "=r"(end_ptr));
> > > 
> > > Why not __image_copy_start/end instead? I know that the result will be the
> > > same
> > > here, but the naming would be more appropriate. The existing u-boot-spl.lds
> > > still gives access to __image_copy_*.
> > 
> > Well, yes, the naming seems appropriate, and I thought and said so
> > myself some time ago. But then, I realize that __image_copy_start and
> > __image_copy_end are tightly coupled with relocation, and I want to
> > avoid creating any additional ties between relocation and SPL just when
> > I am severing them. IOW, I want to keep the option of having a reduced
> > SPL linker file, distinct from the u-boot one, and where none of
> > __image_copy_*, __rel_dyn_* or __dynsym_start exist.
> 
> OK, that's fine.
> 
> Since _end is linker-generated contrary to the other symbols that you use in
> those asm lines, have you checked that no R_ARM_ABS32 relocation data is
> generated here? OTOH, -pie is not used with SPL, so there should be no
> relocation data at all generated here, and the true final addresses should be in
> the binary image.

Indeed, SPL is meant to be loaded at its link-time address -- or, in the
case of mx31pdk and tx25, loaded in a read buffer then moved by itself
to its link-time address. In no case is SPL supposed to be relocated.
You can verify with readelf -r that no relocation records are generated
for SPL builds.

> Best regards,
> Benoît

Amicalement,
-- 
Albert.