Re: [Qemu-devel] [PATCH] hw/acpi/nvdimm: Don't take address of fields in packed structs

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

On Mon, Nov 12, 2018 at 02:42:16PM +0000, Peter Maydell wrote:
> Since nobody responded to my ping of a week ago I propose to just
> apply this to master...
> 
> thanks
> -- PMM

Sorry. My LPC talk proposal suddenly got accepted and
I was scrambling to get ready.

Please feel free to apply this for now:

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>

Generally I think we need to rethink our approach to endian-ness. I
think we want to tag fields with specific endian-ness and use static
checkers to verify it. That is how Linux does it.
In particular this will mean no swapping bytes in place.

But that's a subject for another day.


> On 5 November 2018 at 14:40, Peter Maydell <peter.maydell@linaro.org> wrote:
> > Ping? This patch got reviewed but does not seem to have
> > made it into anybody's tree.
> >
> > thanks
> > -- PMM
> >
> > On 16 October 2018 at 18:52, Peter Maydell <peter.maydell@linaro.org> wrote:
> >> Taking the address of a field in a packed struct is a bad idea, because
> >> it might not be actually aligned enough for that pointer type (and
> >> thus cause a crash on dereference on some host architectures). Newer
> >> versions of clang warn about this. Avoid the bug by not using the
> >> "modify in place" byte swapping functions.
> >>
> >> Patch produced with scripts/coccinelle/inplace-byteswaps.cocci.
> >>
> >> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> >> ---
> >> Automatically generated patch, tested with "make check" only.
> >>
> >>  hw/acpi/nvdimm.c | 16 ++++++++--------
> >>  1 file changed, 8 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/hw/acpi/nvdimm.c b/hw/acpi/nvdimm.c
> >> index 27eeb6609f5..e53b2cb6819 100644
> >> --- a/hw/acpi/nvdimm.c
> >> +++ b/hw/acpi/nvdimm.c
> >> @@ -581,7 +581,7 @@ static void nvdimm_dsm_func_read_fit(AcpiNVDIMMState *state, NvdimmDsmIn *in,
> >>      int size;
> >>
> >>      read_fit = (NvdimmFuncReadFITIn *)in->arg3;
> >> -    le32_to_cpus(&read_fit->offset);
> >> +    read_fit->offset = le32_to_cpu(read_fit->offset);
> >>
> >>      fit = fit_buf->fit;
> >>
> >> @@ -742,8 +742,8 @@ static void nvdimm_dsm_get_label_data(NVDIMMDevice *nvdimm, NvdimmDsmIn *in,
> >>      int size;
> >>
> >>      get_label_data = (NvdimmFuncGetLabelDataIn *)in->arg3;
> >> -    le32_to_cpus(&get_label_data->offset);
> >> -    le32_to_cpus(&get_label_data->length);
> >> +    get_label_data->offset = le32_to_cpu(get_label_data->offset);
> >> +    get_label_data->length = le32_to_cpu(get_label_data->length);
> >>
> >>      nvdimm_debug("Read Label Data: offset %#x length %#x.\n",
> >>                   get_label_data->offset, get_label_data->length);
> >> @@ -781,8 +781,8 @@ static void nvdimm_dsm_set_label_data(NVDIMMDevice *nvdimm, NvdimmDsmIn *in,
> >>
> >>      set_label_data = (NvdimmFuncSetLabelDataIn *)in->arg3;
> >>
> >> -    le32_to_cpus(&set_label_data->offset);
> >> -    le32_to_cpus(&set_label_data->length);
> >> +    set_label_data->offset = le32_to_cpu(set_label_data->offset);
> >> +    set_label_data->length = le32_to_cpu(set_label_data->length);
> >>
> >>      nvdimm_debug("Write Label Data: offset %#x length %#x.\n",
> >>                   set_label_data->offset, set_label_data->length);
> >> @@ -877,9 +877,9 @@ nvdimm_dsm_write(void *opaque, hwaddr addr, uint64_t val, unsigned size)
> >>      in = g_new(NvdimmDsmIn, 1);
> >>      cpu_physical_memory_read(dsm_mem_addr, in, sizeof(*in));
> >>
> >> -    le32_to_cpus(&in->revision);
> >> -    le32_to_cpus(&in->function);
> >> -    le32_to_cpus(&in->handle);
> >> +    in->revision = le32_to_cpu(in->revision);
> >> +    in->function = le32_to_cpu(in->function);
> >> +    in->handle = le32_to_cpu(in->handle);
> >>
> >>      nvdimm_debug("Revision %#x Handler %#x Function %#x.\n", in->revision,
> >>                   in->handle, in->function);
> >> --