Re: [Qemu-devel] [PATCH v2] tests/bios-tables-test: Fix endianess problems when passing data to iasl

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Nov 21, 2017 at 04:58:09PM +0100, Igor Mammedov wrote:
> On Tue, 21 Nov 2017 16:47:11 +0200
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Tue, Nov 21, 2017 at 02:26:39PM +0100, Igor Mammedov wrote:
> > > On Mon, 20 Nov 2017 22:32:29 +0200
> > > "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > >   
> > > > On Mon, Nov 20, 2017 at 05:55:22PM +0100, Igor Mammedov wrote:  
> > > > > On Thu, 16 Nov 2017 13:17:02 +0100
> > > > > Thomas Huth <thuth@redhat.com> wrote:
> > > > >     
> > > > > > The bios-tables-test was writing out files that we pass to iasl in
> > > > > > with the wrong endianness in the header when running on a big endian
> > > > > > host. So instead of storing mixed endian information in our structures,
> > > > > > let's keep everything in little endian and byte-swap it only when we
> > > > > > need a value in the code.
> > > > > > 
> > > > > > Reported-by: Daniel P. Berrange <berrange@redhat.com>
> > > > > > Buglink: https://bugs.launchpad.net/qemu/+bug/1724570
> > > > > > Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> > > > > > Signed-off-by: Thomas Huth <thuth@redhat.com>
> > > > > > ---
> > > > > >  v2: Fixed vmgenid-test which was accidentially broken in v1
> > > > > > 
> > > > > >  tests/acpi-utils.h       | 27 +++++----------------------
> > > > > >  tests/bios-tables-test.c | 42 ++++++++++++++++++++++--------------------
> > > > > >  tests/vmgenid-test.c     | 22 ++++++++++++----------
> > > > > >  3 files changed, 39 insertions(+), 52 deletions(-)
> > > > > > 
> > > > > > diff --git a/tests/acpi-utils.h b/tests/acpi-utils.h
> > > > > > index f8d8723..d5ca5b6 100644
> > > > > > --- a/tests/acpi-utils.h
> > > > > > +++ b/tests/acpi-utils.h
> > > > > > @@ -28,24 +28,9 @@ typedef struct {
> > > > > >      bool tmp_files_retain;   /* do not delete the temp asl/aml */
> > > > > >  } AcpiSdtTable;
> > > > > >  
> > > > > > -#define ACPI_READ_FIELD(field, addr)           \
> > > > > > -    do {                                       \
> > > > > > -        switch (sizeof(field)) {               \
> > > > > > -        case 1:                                \
> > > > > > -            field = readb(addr);               \
> > > > > > -            break;                             \
> > > > > > -        case 2:                                \
> > > > > > -            field = readw(addr);               \
> > > > > > -            break;                             \
> > > > > > -        case 4:                                \
> > > > > > -            field = readl(addr);               \
> > > > > > -            break;                             \
> > > > > > -        case 8:                                \
> > > > > > -            field = readq(addr);               \
> > > > > > -            break;                             \
> > > > > > -        default:                               \
> > > > > > -            g_assert(false);                   \
> > > > > > -        }                                      \    
> > > > > probably it's been discussed but, why not do
> > > > >  leXX_to_cpu()
> > > > > here, instead of making each place that access read field
> > > > > to do leXX_to_cpu() manually.?
> > > > > 
> > > > > Beside of keeping access to structure in natural host order,
> > > > > it should also be less error-prone as field users don't
> > > > > have to worry about endianness.    
> > > > 
> > > > Yes, I suggested that.
> > > > The issue is that we don't byte-swap all of the tables
> > > > (we can't, that would require a full ACPI parser).
> > > > So when byte-swapping we end up with a mixed host/LE
> > > > structures.  
> ...
> > > What tables/use-cases do you have in mind where we'd need full
> > > ACPI parser /whatever it is/?  
> > 
> > We dump ACPI tables for parsing by iasl.
> I don't really see a problem here (i.e. how dumping blobs for
> iasl would require byte-swap all of the tables).

It's not all the tables. We would need to track what is and
what isn't swapped.

> Where bios-tables-test.c is concerned we should just read
> a blob from qemu (get its location/len/name) and dump it to
> disk without changing anything in it.

Exactly.

> > >   
> > > > Keeping it all LE seems cleaner.
> > > > 
> > > >