Hi Julien,
> On 7 Sep 2022, at 09:26, Julien Grall <jul...@xen.org> wrote:
>
> Hi Leo,
>
> On 06/09/2022 12:31, Leo Yan wrote:
>> On Arm64 Linux kernel prints log for Xen version number:
>> [ 0.000000] Xen XEN_VERSION.XEN_SUBVERSION support found
>> Because the header file "xen/compile.h" is missed, XEN_VERSION and
>> XEN_SUBVERSION are not defined, thus compiler directly uses the
>> string "XEN_VERSION" and "XEN_SUBVERSION" in the compatible string.
>> This patch includes the header "xen/compile.h" which defines macros for
>> XEN_VERSION and XEN_SUBVERSION, thus Xen can pass the version number via
>> hypervisor node.
>> Signed-off-by: Leo Yan <leo....@linaro.org>
>
> AFAICT, the problem was introduced when we split the ACPI code from
> arch/domain_build.c. So I would add the following tag:
>
> Fixes: 5d797ee199b3 ("xen/arm: split domain_build.c")
>
> Now, this means we shipped Xen for ~4 years with the wrong compatible. The
> compatible is meant to indicate the Xen version. However, I don't think this
> is used for anything other than printing the version on the console.
>
> Also, the problem occurs only when using ACPI. This is still in tech preview,
> so I think we don't need to document the issue in the documentation (we can
> easily break ABI).
>
>> ---
>> xen/arch/arm/acpi/domain_build.c | 1 +
>> 1 file changed, 1 insertion(+)
>> diff --git a/xen/arch/arm/acpi/domain_build.c
>> b/xen/arch/arm/acpi/domain_build.c
>> index bbdc90f92c..2649e11fd4 100644
>> --- a/xen/arch/arm/acpi/domain_build.c
>> +++ b/xen/arch/arm/acpi/domain_build.c
>> @@ -9,6 +9,7 @@
>> * GNU General Public License for more details.
>> */
>> +#include <xen/compile.h>
>
> So this is fixing the immediate problem. Given the subtlety of the bug, I
> think it would be good to also harden the code at the same time.
I think we should commit the patch as is and harden the code in a subsequent
patch.
>
> I can see two way to do that:
> 1) Dropping the use of __stringify
> 2) Check if XEN_VERSION and XEN_SUBVERSION are defined
>
> The latter is probably lightweight. This could be added right next to
> acpi_make_hypervisor_node() for clarify.
>
> Something like:
>
> #ifndef XEN_VERSION
> # error "XEN_VERSION is not defined"
> #endif
>
> #ifndef XEN_SUBVERSION
> # error "XEN_SUBVERSION is not defined"
> #endif
>
> Could you have a look?
There are actually several places in the code where we use the stringify system.
Would it make sense to actually have a string version provided in compile.h and
use it instead ?
Otherwise if we start adding those kinds of checks, we will have to add them in
at least 3 places in xen code.
Cheers
Bertrand
>
>> #include <xen/mm.h>
>> #include <xen/sched.h>
>> #include <xen/acpi.h>
>
> Cheers,
>
> --
> Julien Grall
