On Thu, Jul 04, 2024 at 01:15:57PM +0100, Peter Maydell wrote:
> On Sat, 29 Jun 2024 at 04:17, David Gibson <da...@gibson.dropbear.id.au>
> wrote:
> >
> > On Fri, Jun 28, 2024 at 04:20:02PM +0100, Peter Maydell wrote:
> > > On Thu, 27 Jun 2024 at 14:39, Akihiko Odaki <akihiko.od...@daynix.com>
> > > wrote:
> > > >
> > > > FDT properties are aligned by 4 bytes, not 8 bytes.
> > > >
> > > > Signed-off-by: Akihiko Odaki <akihiko.od...@daynix.com>
> > > > ---
> > > > hw/ppc/vof.c | 2 +-
> > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/hw/ppc/vof.c b/hw/ppc/vof.c
> > > > index e3b430a81f4f..b5b6514d79fc 100644
> > > > --- a/hw/ppc/vof.c
> > > > +++ b/hw/ppc/vof.c
> > > > @@ -646,7 +646,7 @@ static void vof_dt_memory_available(void *fdt,
> > > > GArray *claimed, uint64_t base)
> > > > mem0_reg = fdt_getprop(fdt, offset, "reg", &proplen);
> > > > g_assert(mem0_reg && proplen == sizeof(uint32_t) * (ac + sc));
> > > > if (sc == 2) {
> > > > - mem0_end = be64_to_cpu(*(uint64_t *)(mem0_reg +
> > > > sizeof(uint32_t) * ac));
> > > > + mem0_end = ldq_be_p(mem0_reg + sizeof(uint32_t) * ac);
> > > > } else {
> > > > mem0_end = be32_to_cpu(*(uint32_t *)(mem0_reg +
> > > > sizeof(uint32_t) * ac));
> > > > }
> > >
> > > I did wonder if there was a better way to do what this is doing,
> > > but neither we (in system/device_tree.c) nor libfdt seem to
> > > provide one.
> >
> > libfdt does provide unaligned access helpers (fdt32_ld() etc.), but
> > not an automatic aligned-or-unaligned helper. Maybe we should add that?
>
> fdt32_ld() and friends only do the "load from this bit of memory"
> part, which we already have QEMU utility functions for (and which
> are this patch uses).
>
> This particular bit of code is dealing with an fdt property ("memory")
> that is an array of (address, size) tuples where address and size
> can independently be either 32 or 64 bits, and it wants the
> size value of tuple 0. So the missing functionality is something at
> a higher level than fdt32_ld() which would let you say "give me
> tuple N field X" with some way to specify the tuple layout. (Which
> is an awkward kind of API to write in C.)Ah, right. Yeah.. that's a pretty awkward API in C. > Slightly less general, but for this case we could perhaps have > something like the getprop equivalent of qemu_fdt_setprop_sized_cells(): > > uint64_t value_array[2]; > qemu_fdt_getprop_sized_cells(fdt, nodename, "memory", &value_array, > ac, sc); > /* > * fills in value_array[0] with address, value_array[1] with size, > * probably barfs if the varargs-list of cell-sizes doesn't > * cover the whole property, similar to the current assert on > * proplen. > */ > mem0_end = value_array[0]; Seems reasonable to me. The only other thought I had was something like Python's struct.unpack() [0]. But your suggestion is probably more natural in C. [0] https://docs.python.org/3/library/struct.html#struct.unpack -- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson
signature.asc
Description: PGP signature
