On 07/09/2022 09:30, Bertrand Marquis wrote:
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 thought about this. However, if we do the hardening in the same patch,
then it makes a lot easier to confirm that the patch works when ingested
in downstream code or backported.
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 ?
I think so.
Otherwise if we start adding those kinds of checks, we will have to add them in
at least 3 places in xen code.
The solution I proposed above is easy to implement right now. My gut
feeling is tweaking __stringify (or else) will take a bit more time.
If you (or Leo) can come up with a solution quickly then fine.
Otherwise, I think we still want some hardening for backporting purpose.
Cheers,
--
Julien Grall
