Re: [Qemu-devel] [PATCH v1 1/1] riscv: virt: Cast the initrd start address to target bit length

[Alistair Francis]

On Wed, Nov 21, 2018 at 5:58 PM Palmer Dabbelt <address@hidden> wrote:
>
> On Wed, 21 Nov 2018 14:34:44 PST (-0800), Alistair Francis wrote:
> > Ensure that the calculate initrd offset points to a valid address for
> > the architecture.
> >
> > Signed-off-by: Alistair Francis <address@hidden>
> > Suggested-by: Alexander Graf <address@hidden>
> > Reported-by: Alexander Graf <address@hidden>
> > ---
> >  hw/riscv/virt.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
> > index 2b38f89070..4467195fac 100644
> > --- a/hw/riscv/virt.c
> > +++ b/hw/riscv/virt.c
> > @@ -85,7 +85,12 @@ static hwaddr load_initrd(const char *filename, uint64_t 
> > mem_size,
> >       * halfway into RAM, and for boards with 256MB of RAM or more we put
> >       * the initrd at 128MB.
> >       */
> > -    *start = kernel_entry + MIN(mem_size / 2, 128 * MiB);
> > +    /* As hwaddr is a 64-bit number we need to cast it for 32-bit */
> > +#if defined(TARGET_RISCV32)
> > +    *start = (uint32_t) (kernel_entry + MIN(mem_size / 2, 128ULL * MiB));
> > +#elif defined(TARGET_RISCV64)
> > +    *start = (uint64_t) (kernel_entry + MIN(mem_size / 2, 128 * MiB));
> > +#endif
> >
> >      size = load_ramdisk(filename, *start, mem_size - *start);
> >      if (size == -1) {
> > --
> > 2.19.1
>
> Maybe I'm missing something, but wouldn't something like
>
>     uint64_t start_unclobbered = kernel_entry + MIN(mem_size / 2, 128ULL * 
> MiB);
>     assert(start_unclobbered == (hwaddr)start_unclobbered);
>     *start = (hwaddr)start_unclobbered;
>
> work better?  That should actually check this all lines up, as opposed to just
> silently truncating a bad address.

The problem is that hwaddr is always 64-bit.

Stupidly I forgot about target_ulong, which should work basically the
same as above. An assert() seems a little harsh though, Alex reported
problem was fixed with just a cast.

Alistair