[U-Boot] [PATCH v2 2/3] arm: relocate the exception vectors

Tue Oct 21 15:54:51 CEST 2014

Hi Georges,

On Mon, 20 Oct 2014 23:08:30 +0200, Georges Savoundararadj
<savoundg at gmail.com> wrote:

> Hi Albert,
> 
> Le 15/10/2014 00:11, Albert ARIBAUD a écrit :
> > Hi Georges,
> >
> > On Tue, 14 Oct 2014 22:02:00 +0200, Georges Savoundararadj
> > <savoundg at gmail.com> wrote:
> >
> >> Hi Albert,
> >>
> >> Hi Masahiro,
> > (putting Masahiro in Cc: just in case)
> >
> >> As my issue is related to Kconfig, I would like you to give me your
> >> opinions.
> >>
> >>
> >> Le 11/10/2014 12:47, Albert ARIBAUD a écrit :
> >>> Hi Georges,
> >>>
> >>> On Sat, 27 Sep 2014 21:48:10 +0200, Georges Savoundararadj
> >>> <savoundg at gmail.com> wrote:
> >>>
> >>>> This commit relocates the exception vectors.
> >>>> As ARM1176 and ARMv7 have the security extensions, it uses VBAR.  For
> >>>> the other ARM processors, it copies the relocated exception vectors to
> >>>> the correct address: 0x00000000 or 0xFFFF0000.
> >>>>
> >>>> Signed-off-by: Georges Savoundararadj <savoundg at gmail.com>
> >>>> Cc: Albert Aribaud <albert.u.boot at aribaud.net>
> >>>> Cc: Tom Warren <twarren at nvidia.com>
> >>>>
> >>>> ---
> >>>> This patch needs some tests because it impacts many boards. I have
> >>>> tested it with my raspberry pi in the two cases: using VBAR and
> >>>> using the copied exception vectors.
> >>>>
> >>>> Changes in v2:
> >>>> - Relocate exception vectors also on processors which do not support
> >>>>     security extensions
> >>>> - Reword the commit message
> >>>>
> >>>>    arch/arm/cpu/armv7/start.S |  6 ------
> >>>>    arch/arm/lib/relocate.S    | 30 ++++++++++++++++++++++++++++++
> >>>>    2 files changed, 30 insertions(+), 6 deletions(-)
> >>>>
> >>>> diff --git a/arch/arm/cpu/armv7/start.S b/arch/arm/cpu/armv7/start.S
> >>>> index fedd7c8..fdc05b9 100644
> >>>> --- a/arch/arm/cpu/armv7/start.S
> >>>> +++ b/arch/arm/cpu/armv7/start.S
> >>>> @@ -81,12 +81,6 @@ ENTRY(c_runtime_cpu_setup)
> >>>>    	mcr     p15, 0, r0, c7, c10, 4	@ DSB
> >>>>    	mcr     p15, 0, r0, c7, c5, 4	@ ISB
> >>>>    #endif
> >>>> -/*
> >>>> - * Move vector table
> >>>> - */
> >>>> -	/* Set vector address in CP15 VBAR register */
> >>>> -	ldr     r0, =_start
> >>>> -	mcr     p15, 0, r0, c12, c0, 0  @Set VBAR
> >>>>    
> >>>>    	bx	lr
> >>>>    
> >>>> diff --git a/arch/arm/lib/relocate.S b/arch/arm/lib/relocate.S
> >>>> index 8035251..88a478e 100644
> >>>> --- a/arch/arm/lib/relocate.S
> >>>> +++ b/arch/arm/lib/relocate.S
> >>>> @@ -6,6 +6,8 @@
> >>>>     * SPDX-License-Identifier:	GPL-2.0+
> >>>>     */
> >>>>    
> >>>> +#include <asm-offsets.h>
> >>>> +#include <config.h>
> >>>>    #include <linux/linkage.h>
> >>>>    
> >>>>    /*
> >>>> @@ -52,6 +54,34 @@ fixnext:
> >>>>    	cmp	r2, r3
> >>>>    	blo	fixloop
> >>>>    
> >>>> +	/*
> >>>> +	 * Relocate the exception vectors
> >>>> +	 */
> >>>> +#if (defined(CONFIG_ARM1176) || defined(CONFIG_ARMV7))
> >>> I would prefer a single CONFIG_HAS_VBAR symbol defined through
> >>> Kconfig.
> >> 1)
> >> Actually, there is no Kconfig entry such as "config ARM1176" nor "config
> >> ARMV7" in U-Boot,
> >> unlike in Linux (arch/arm/mm/Kconfig).
> >>
> >> If there were such entries, we would simply do like the following (in
> >> arch/arm/Kconfig):
> >>
> >> config HAS_VBAR
> >>       bool
> >>
> >> config ARM1176
> >>       select HAS_VBAR
> >>
> >> config ARMV7
> >>       select HAS_VBAR
> >>
> >> Should we go in this direction?
> >> It is the cleanest way to use Kconfig but it requires some work in order
> >> to convert all
> >> "#define CONFIG_<cpu>" into Kconfig entries.
> >>
> >> 2)
> >> Otherwise, we can insert a "select HAS_VBAR" in all boards that have a
> >> ARM1176 or a ARMv7
> >> processor in arch/arm/Kconfig. It is not logical but this is what has
> >> been done with the Kconfig
> >> entry ARM64. And, it does not require much change.
> >>
> >> 3)
> >> The last thing we can do is as follows:
> >>
> >> config HAS_VBAR
> >>           bool
> >>           depends on SYS_CPU = "arm1176" || SYS_CPU = "armv7"
> >>           default y
> >>
> >> CONFIG_HAS_VBAR will be defined if SYS_CPU are arm1176 or armv7. It does
> >> not require much
> >> change as well but, I think, it is bad code.
> >>
> >> What do you think is the best way to introduce CONFIG_HAS_VBAR symbol?
> >> (1, 2 or 3)
> > I believe you have already sorted the options in order of decreasing
> > 'quality' -- 1 being the best option, and 3 being the worst... Indeed
> > option 1 would be the best and cleanest, and it could possibly open the
> > way for other per-CPU options.
> >
> > We could try and limit the effort to converting only ARM1176 and ARMV7
> > and leaving other CONFIG_<cpu> #define'd until some later point in the
> > future, but experience shows that such half-hearted attempts are never
> > completed.
> >
> > Amicalement,
> 
> I am currently trying to implement solution 1. only for ARM1176 and 
> ARMV7 but I wonder
> if this work worth the effort just for one CPU feature.
> Do you expect more CPU feature like HAS_VBAR coming in the future?
> 
> I add the following lines in arch/arm/Kconfig:
> config HAS_VBAR
>         bool
> 
> config ARM1176
>         bool
>         select HAS_VBAR
> 
> config ARMV7
>          bool
>          select HAS_VBAR
> 
> config SYS_CPU
>         default "arm1176" if ARM1176
>         default "armv7" if ARMV7
> 
> Then, in the same file, under each "config TARGET_<board>",  I add 
> "select ARM1176" or "select ARMV7".
> Also, I delete the Kconfig entries "config SYS_CPU" in all Kconfig of 
> *all* boards that use ARM1176 and ARMV7.
> 
> Actually, I find the change quite big. What do you think about this 
> implementation?
> Should I continue in this direction?

This looks like the right way to me (even if ideally I would prefer
that SYS_CPU be deduced from the SYS_SOC defined in the boards' Kconfig
files rather than added to them).

Hopefully you can devise a sed, awk o perl script to do the change
without too much manual effort?

Incidentally, this raises a question which Masahiro can probably
answer. In arch/arm/Kconfig, every ARM board is referred to twice:

- once in a "config TARGET_<board>" block;

- once in a "source board[/<maker>]/<board>/Kconfig directive.

Would it be possible to move each "TARGET_<board>" block from
arch/arm/Kconfig to the corresponding board[/<maker>]/<board>/Kconfig
and only keep the "source" directives in arch/arm/Kconfig?

(and then, I'd *really* like a way to source all ARM-based boards in a
few lines, e.g. source /board/*/Kconfig + source board/*/*/Kconfig)

It would be nice if all Kconfig settings for a given board were found
in the board's Kconfig.

> Regards,
> 
> Georges

Amicalement,
-- 
Albert.