From: Julien Grall <jgrall@xxxxxxxxxx>
The documentation of pvcalls suggests there is padding for 32-bit x86
at the end of most the structure. However, they are not described in
in the public header.
Because of that all the structures would be 32-bit aligned and not
64-bit aligned for 32-bit x86.
For all the other architectures supported (Arm and 64-bit x86), the
structure are aligned to 64-bit because they contain uint64_t field.
Therefore all the structures contain implicit padding.
The paddings are now corrected for 32-bit x86 and written explicitly for
all the architectures.
While the structure size between 32-bit and 64-bit x86 is different, it
shouldn't cause any incompatibility between a 32-bit and 64-bit
frontend/backend because the commands are always 56 bits and the padding
are at the end of the structure.
As an aside, the padding sadly cannot be mandated to be 0 as they are
already present. So it is not going to be possible to use the padding
for extending a command in the future.
Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
---
Changes in v2:
- It is not possible to use the same padding for 32-bit x86 and
all the other supported architectures.
---
docs/misc/pvcalls.pandoc | 18 ++++++++++--------
xen/include/public/io/pvcalls.h | 14 ++++++++++++++
2 files changed, 24 insertions(+), 8 deletions(-)
diff --git a/docs/misc/pvcalls.pandoc b/docs/misc/pvcalls.pandoc
index 665dad556c39..c25412868f5d 100644
--- a/docs/misc/pvcalls.pandoc
+++ b/docs/misc/pvcalls.pandoc
@@ -246,9 +246,9 @@ The format is defined as follows:
uint32_t domain;
uint32_t type;
uint32_t protocol;
- #ifdef CONFIG_X86_32
+ #ifndef CONFIG_X86_32
uint8_t pad[4];
- #endif
+ #endif
} socket;
struct xen_pvcalls_connect {
uint64_t id;
@@ -257,16 +257,18 @@ The format is defined as follows:
uint32_t flags;
grant_ref_t ref;
uint32_t evtchn;
- #ifdef CONFIG_X86_32
+ #ifndef CONFIG_X86_32
uint8_t pad[4];
- #endif
+ #endif
} connect;
struct xen_pvcalls_release {
uint64_t id;
uint8_t reuse;
- #ifdef CONFIG_X86_32
+ #ifndef CONFIG_X86_32
uint8_t pad[7];
- #endif
+ #else
+ uint8_t pad[3];
+ #endif
} release;
struct xen_pvcalls_bind {
uint64_t id;
@@ -276,9 +278,9 @@ The format is defined as follows:
struct xen_pvcalls_listen {
uint64_t id;
uint32_t backlog;
- #ifdef CONFIG_X86_32
+ #ifndef CONFIG_X86_32
uint8_t pad[4];
- #endif
+ #endif
} listen;
struct xen_pvcalls_accept {
uint64_t id;
diff --git a/xen/include/public/io/pvcalls.h b/xen/include/public/io/pvcalls.h
index cb8171275c13..590c5e9e41aa 100644
--- a/xen/include/public/io/pvcalls.h
+++ b/xen/include/public/io/pvcalls.h
@@ -65,6 +65,9 @@ struct xen_pvcalls_request {
uint32_t domain;
uint32_t type;
uint32_t protocol;
+#ifndef CONFIG_X86_32
+ uint8_t pad[4];
+#endif
} socket;
struct xen_pvcalls_connect {
uint64_t id;
@@ -73,10 +76,18 @@ struct xen_pvcalls_request {
uint32_t flags;
grant_ref_t ref;
uint32_t evtchn;
+#ifndef CONFIG_X86_32
+ uint8_t pad[4];
+#endif
} connect;
struct xen_pvcalls_release {
uint64_t id;
uint8_t reuse;
+#ifndef CONFIG_X86_32
+ uint8_t pad[7];
+#else
+ uint8_t pad[3];
+#endif
} release;
struct xen_pvcalls_bind {
uint64_t id;
@@ -86,6 +97,9 @@ struct xen_pvcalls_request {
struct xen_pvcalls_listen {
uint64_t id;
uint32_t backlog;
+#ifndef CONFIG_X86_32
+ uint8_t pad[4];
+#endif
} listen;
struct xen_pvcalls_accept {
uint64_t id;
