Hi,
On Fri, Jun 17, 2022 at 05:38:01PM -0700, Ricardo Koller wrote:
> Hi Nikos,
>
> On Fri, May 06, 2022 at 09:55:45PM +0100, Nikos Nikoleris wrote:
> > XSDT provides pointers to other ACPI tables much like RSDT. However,
> > contrary to RSDT that provides 32-bit addresses, XSDT provides 64-bit
> > pointers. ACPI requires that if XSDT is valid then it takes precedence
> > over RSDT.
> >
> > Signed-off-by: Nikos Nikoleris <nikos.nikoleris@xxxxxxx>
> > ---
> > lib/acpi.h | 6 ++++
> > lib/acpi.c | 103 ++++++++++++++++++++++++++++++++---------------------
> > 2 files changed, 68 insertions(+), 41 deletions(-)
> >
> > diff --git a/lib/acpi.h b/lib/acpi.h
> > index 42a2c16..d80b983 100644
> > --- a/lib/acpi.h
> > +++ b/lib/acpi.h
> > @@ -13,6 +13,7 @@
> >
> > #define RSDP_SIGNATURE ACPI_SIGNATURE('R','S','D','P')
> > #define RSDT_SIGNATURE ACPI_SIGNATURE('R','S','D','T')
> > +#define XSDT_SIGNATURE ACPI_SIGNATURE('X','S','D','T')
> > #define FACP_SIGNATURE ACPI_SIGNATURE('F','A','C','P')
> > #define FACS_SIGNATURE ACPI_SIGNATURE('F','A','C','S')
> >
> > @@ -56,6 +57,11 @@ struct rsdt_descriptor_rev1 {
> > u32 table_offset_entry[0];
> > } __attribute__ ((packed));
> >
> > +struct acpi_table_xsdt {
> > + ACPI_TABLE_HEADER_DEF
> > + u64 table_offset_entry[1];
>
> nit: This should be "[0]" to match the usage above (in rsdt).
>
> I was about to suggest using an unspecified size "[]", but after reading
> what the C standard says about it (below), now I'm not sure. was the
> "[1]" needed for something that I'm missing?
>
> 106) The length is unspecified to allow for the fact that
> implementations may give array members different
> alignments according to their lengths.
GCC prefers "flexible array members" (array[]) [1]. Linux has deprecated
the use of zero-length arrays [2]. The kernel docs do make a pretty good
case for flexible array members.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://elixir.bootlin.com/linux/v5.18/source/Documentation/process/deprecated.rst#L234
Thanks,
Alex
