Re: [PATCH] generic-loader: remove the ram_size limit when a loading binary file

[Damien Hedde]

On 10/7/21 08:41, Alistair Francis wrote:
> On Wed, Oct 6, 2021 at 10:04 PM Damien Hedde <damien.hedde@greensocs.com> wrote:
> > On 10/6/21 13:49, Philippe Mathieu-Daudé wrote:
> > > On 10/6/21 13:37, Damien Hedde wrote:
> > > > Right now, we cannot load some binary file if it is bigger than the
> > > > machine's ram size. This limitation only occurs when loading a
> > > > binary file: we can load a corresponding elf file without this
> > > > limitation.
> > > >
> > > > This is an issue for machines that have small ram or do not use the
> > > > ram_size feature at all.
> > > >
> > > > Also get rid of "hw/boards.h" include, since we needed it only
> > > > to access `current_machine`.
> > > >
> > > > Fixes: e481a1f63c9 ("generic-loader: Add a generic loader")
> > > > Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
> > > > ---
> > > >
> > > > Hi Alistair,
> > > >
> > > > I found this while experimenting with a ram_size=0 machine.
> >
> >
> >
> > > Where are you loading your file?
> >
> > In a rom.
> >
> > The loader does not check at all that we are loading to the machine's
> > ram. It just check the size for the raw binary file format.
>
> Hmmm... This is probably correct, in that a user might want to load a
> binary into ROM and doesn't want to be blocked by the ram size.
>
> In general though a user would expect an error if they are loading a
> file into RAM that is larger then the RAM. So I'm not fully convinced
> we want this change.

I do agree for the error, but right now if you give a wrong base 
address, it does not fail (see below).

I can give a look to see if such check would be possible.

> What error do you get if you try to load a binary that is too large
> with this patch applied?

Nothing if you pass the ram_size check. You can even try to load 
something to an unmapped area, it doesn't report an error.

But it does not do anything visible to the guest I suppose (in the 
monitor, x/'xp' commands still tell you it cannot access the memory if 
you tried to load it somewhere that does not exist).

If you try to load something bigger than the target region, the region 
seems to be initialized.

Thanks,
Damien

> Alistair
>
> > --
> > Damien