[U-Boot] [PATCH v2 07/29] riscv: add Kconfig entries for the code model

[Auer, Lukas]

Hi Bin,

On Tue, 2018-11-13 at 15:34 +0800, Bin Meng wrote:
> Hi Lukas,
> 
> On Wed, Oct 31, 2018 at 11:01 PM Auer, Lukas
> <lukas.auer at aisec.fraunhofer.de> wrote:
> > 
> > Hi Bin,
> > 
> > On Wed, 2018-10-31 at 10:13 +0800, Bin Meng wrote:
> > > Hi Lukas,
> > > 
> > > On Tue, Oct 30, 2018 at 8:57 PM Lukas Auer
> > > <lukas.auer at aisec.fraunhofer.de> wrote:
> > > > 
> > > > RISC-V has two code models, medium low (medlow) and medium any
> > > > (medany).
> > > > Medlow limits addressable memory to a single 2 GiB range
> > > > between
> > > > the
> > > > absolute addresses -2 GiB and +2 GiB. Medany limits addressable
> > > > memory
> > > > to any single 2 GiB address range.
> > > > By default, medlow is selected on 32-bit systems and medany on
> > > > 64-
> > > > bit
> > > > systems. This matches the configuration in Linux.
> > > > 
> > > > The -mcmodel compiler flag is selected according to the Kconfig
> > > > configuration.
> > > > 
> > > > Signed-off-by: Lukas Auer <lukas.auer at aisec.fraunhofer.de>
> > > > ---
> > > > 
> > > > Changes in v2:
> > > > - Change ISA string construction, as suggested by Bin Meng
> > > > 
> > > >  arch/riscv/Kconfig  | 19 +++++++++++++++++++
> > > >  arch/riscv/Makefile |  9 ++++++++-
> > > >  2 files changed, 27 insertions(+), 1 deletion(-)
> > > > 
> > > 
> > > I had a further look at this, and I suspect we should stick to
> > > medlow
> > > for U-Boot, even for 64-bit. As U-Boot will be only running
> > > within
> > > the
> > > low 4GB memory space even for 64-bit. Adding medany seems
> > > unnecessary.
> > > 
> > > Regards,
> > > Bin
> > 
> > You are right, however I think it's actually because U-Boot is
> > compiled
> > as a position independent binary. U-Boot can be relocated above
> > what's
> > addressable with 32-bit if the memory is large enough. This should
> > cause issues with medlow.
> > I suspects that's the reason, but I am not entirely sure. What do
> > you
> > think?
> 
> Sorry I missed this email. I just found in your v3 this patch was
> dropped. I think this is still needed to explicitly pass the code
> model to the compiler. I believe we only need change to:
> 
> +choice
> +       prompt "Code Model"
> +       default CMODEL_MEDLOW
> 
> I can include the modified patch in my upcoming series.
> 
> Regards,
> Bin

Ok, I miss-understood that. Sounds good, thanks!

Lukas