diff mbox series

[v3] xen/public: fix flexible array definitions

Message ID 20231201112041.5260-1-jgross@suse.com (mailing list archive)
State New, archived
Headers show
Series [v3] xen/public: fix flexible array definitions | expand

Commit Message

Jürgen Groß Dec. 1, 2023, 11:20 a.m. UTC
Flexible arrays in public headers can be problematic with some
compilers.

With XEN_FLEX_ARRAY_DIM there is a mechanism available to deal with
this issue, but care must be taken to not change the affected structs
in an incompatible way.

So bump __XEN_LATEST_INTERFACE_VERSION__ and introduce a new macro
XENPV_FLEX_ARRAY_DIM which will be XENPV_FLEX_ARRAY_DIM with the
interface version being new enough and "1" (the value used today in
the affected headers) when the interface version is an old one.

Replace the arr[1] instances (this includes the ones seen to be
problematic in recent Linux kernels [1]) with arr[XENPV_FLEX_ARRAY_DIM]
in order to avoid compilation errors.

[1]: https://bugzilla.kernel.org/show_bug.cgi?id=217693

Signed-off-by: Juergen Gross <jgross@suse.com>
---
V2:
- bump interface version and make change only for new version
  (Jan Beulich)
V3:
- move XENPV_FLEX_ARRAY_DIM definition to ring.h (Jan Beulich)
- fix 2 wrong XENPV_FLEX_ARRAY_DIM use cases (Julien Grall)
- add CHANGELOG.md entry (Andrew Cooper)
---
 CHANGELOG.md                     |  2 ++
 xen/include/public/io/cameraif.h |  2 +-
 xen/include/public/io/displif.h  |  2 +-
 xen/include/public/io/fsif.h     |  4 ++--
 xen/include/public/io/pvcalls.h  |  2 +-
 xen/include/public/io/ring.h     | 12 ++++++++++--
 xen/include/public/io/sndif.h    |  2 +-
 xen/include/public/xen-compat.h  |  2 +-
 8 files changed, 19 insertions(+), 9 deletions(-)

Comments

Henry Wang Dec. 1, 2023, 11:22 a.m. UTC | #1
Hi Juergen,

> On Dec 1, 2023, at 19:20, Juergen Gross <jgross@suse.com> wrote:
> 
> Flexible arrays in public headers can be problematic with some
> compilers.
> 
> With XEN_FLEX_ARRAY_DIM there is a mechanism available to deal with
> this issue, but care must be taken to not change the affected structs
> in an incompatible way.
> 
> So bump __XEN_LATEST_INTERFACE_VERSION__ and introduce a new macro
> XENPV_FLEX_ARRAY_DIM which will be XENPV_FLEX_ARRAY_DIM with the
> interface version being new enough and "1" (the value used today in
> the affected headers) when the interface version is an old one.
> 
> Replace the arr[1] instances (this includes the ones seen to be
> problematic in recent Linux kernels [1]) with arr[XENPV_FLEX_ARRAY_DIM]
> in order to avoid compilation errors.
> 
> [1]: https://bugzilla.kernel.org/show_bug.cgi?id=217693
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>

Acked-by: Henry Wang <Henry.Wang@arm.com> # CHANGELOG

Kind regards,
Henry
Jan Beulich Dec. 1, 2023, 11:25 a.m. UTC | #2
On 01.12.2023 12:20, Juergen Gross wrote:
> Flexible arrays in public headers can be problematic with some
> compilers.
> 
> With XEN_FLEX_ARRAY_DIM there is a mechanism available to deal with
> this issue, but care must be taken to not change the affected structs
> in an incompatible way.
> 
> So bump __XEN_LATEST_INTERFACE_VERSION__ and introduce a new macro
> XENPV_FLEX_ARRAY_DIM which will be XENPV_FLEX_ARRAY_DIM with the
> interface version being new enough and "1" (the value used today in
> the affected headers) when the interface version is an old one.
> 
> Replace the arr[1] instances (this includes the ones seen to be
> problematic in recent Linux kernels [1]) with arr[XENPV_FLEX_ARRAY_DIM]
> in order to avoid compilation errors.
> 
> [1]: https://bugzilla.kernel.org/show_bug.cgi?id=217693
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>

> --- a/xen/include/public/io/ring.h
> +++ b/xen/include/public/io/ring.h
> @@ -25,8 +25,16 @@
>   * and grant_table.h from the Xen public headers.
>   */
>  
> +#include "../xen.h"
>  #include "../xen-compat.h"

Just to mention it: While perhaps good practice, I'm not convinced this
extra #include is actually needed here.

> +/* Some PV I/O interfaces need a compatibility variant. */
> +#if __XEN_INTERFACE_VERSION__ < 0x00041300
> +#define XENPV_FLEX_ARRAY_DIM  1 /* variable size */
> +#else
> +#define XENPV_FLEX_ARRAY_DIM  XEN_FLEX_ARRAY_DIM
> +#endif
> +
>  #if __XEN_INTERFACE_VERSION__ < 0x00030208
>  #define xen_mb()  mb()
>  #define xen_rmb() rmb()
> @@ -110,7 +118,7 @@ struct __name##_sring {                                                 \
>          uint8_t pvt_pad[4];                                             \
>      } pvt;                                                              \
>      uint8_t __pad[44];                                                  \
> -    union __name##_sring_entry ring[1]; /* variable-length */           \
> +    union __name##_sring_entry ring[XENPV_FLEX_ARRAY_DIM];              \
>  };                                                                      \
>                                                                          \
>  /* "Front" end's private variables */                                   \
> @@ -479,7 +487,7 @@ struct name##_data_intf {                                                     \
>      uint8_t pad2[56];                                                         \
>                                                                                \
>      RING_IDX ring_order;                                                      \
> -    grant_ref_t ref[];                                                        \
> +    grant_ref_t ref[XEN_FLEX_ARRAY_DIM];                                      \
>  };                                                                            \
>  DEFINE_XEN_FLEX_RING(name)
>
Julien Grall Dec. 1, 2023, 11:50 a.m. UTC | #3
On 01/12/2023 11:20, Juergen Gross wrote:
> Flexible arrays in public headers can be problematic with some
> compilers.
> 
> With XEN_FLEX_ARRAY_DIM there is a mechanism available to deal with
> this issue, but care must be taken to not change the affected structs
> in an incompatible way.
> 
> So bump __XEN_LATEST_INTERFACE_VERSION__ and introduce a new macro
> XENPV_FLEX_ARRAY_DIM which will be XENPV_FLEX_ARRAY_DIM with the
> interface version being new enough and "1" (the value used today in
> the affected headers) when the interface version is an old one.
> 
> Replace the arr[1] instances (this includes the ones seen to be
> problematic in recent Linux kernels [1]) with arr[XENPV_FLEX_ARRAY_DIM]
> in order to avoid compilation errors.
> 
> [1]: https://bugzilla.kernel.org/show_bug.cgi?id=217693
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>

Acked-by: Julien Grall <jgrall@amazon.com>

Cheers,
diff mbox series

Patch

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4ecebb9f68..5ee5d41fc9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,8 @@  The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ## [4.19.0 UNRELEASED](https://xenbits.xenproject.org/gitweb/?p=xen.git;a=shortlog;h=staging) - TBD
 
 ### Changed
+ - Changed flexible array definitions in public I/O interface headers to not
+   use "1" as the number of array elements.
 
 ### Added
  - On x86:
diff --git a/xen/include/public/io/cameraif.h b/xen/include/public/io/cameraif.h
index 13763abef9..a389443769 100644
--- a/xen/include/public/io/cameraif.h
+++ b/xen/include/public/io/cameraif.h
@@ -763,7 +763,7 @@  struct xencamera_buf_create_req {
  */
 struct xencamera_page_directory {
     grant_ref_t gref_dir_next_page;
-    grant_ref_t gref[1]; /* Variable length */
+    grant_ref_t gref[XENPV_FLEX_ARRAY_DIM];
 };
 
 /*
diff --git a/xen/include/public/io/displif.h b/xen/include/public/io/displif.h
index 73d0cbdf15..132c96fa5c 100644
--- a/xen/include/public/io/displif.h
+++ b/xen/include/public/io/displif.h
@@ -537,7 +537,7 @@  struct xendispl_dbuf_create_req {
 
 struct xendispl_page_directory {
     grant_ref_t gref_dir_next_page;
-    grant_ref_t gref[1]; /* Variable length */
+    grant_ref_t gref[XENPV_FLEX_ARRAY_DIM];
 };
 
 /*
diff --git a/xen/include/public/io/fsif.h b/xen/include/public/io/fsif.h
index ec57850233..dcade1c698 100644
--- a/xen/include/public/io/fsif.h
+++ b/xen/include/public/io/fsif.h
@@ -40,7 +40,7 @@  struct fsif_read_request {
     int32_t pad;
     uint64_t len;
     uint64_t offset;
-    grant_ref_t grefs[1];  /* Variable length */
+    grant_ref_t grefs[XENPV_FLEX_ARRAY_DIM];
 };
 
 struct fsif_write_request {
@@ -48,7 +48,7 @@  struct fsif_write_request {
     int32_t pad;
     uint64_t len;
     uint64_t offset;
-    grant_ref_t grefs[1];  /* Variable length */
+    grant_ref_t grefs[XENPV_FLEX_ARRAY_DIM];
 };
 
 struct fsif_stat_request {
diff --git a/xen/include/public/io/pvcalls.h b/xen/include/public/io/pvcalls.h
index 230b0719e3..c8c7602470 100644
--- a/xen/include/public/io/pvcalls.h
+++ b/xen/include/public/io/pvcalls.h
@@ -30,7 +30,7 @@  struct pvcalls_data_intf {
     uint8_t pad2[52];
 
     RING_IDX ring_order;
-    grant_ref_t ref[];
+    grant_ref_t ref[XEN_FLEX_ARRAY_DIM];
 };
 DEFINE_XEN_FLEX_RING(pvcalls);
 
diff --git a/xen/include/public/io/ring.h b/xen/include/public/io/ring.h
index 0cae4367be..a79d913142 100644
--- a/xen/include/public/io/ring.h
+++ b/xen/include/public/io/ring.h
@@ -25,8 +25,16 @@ 
  * and grant_table.h from the Xen public headers.
  */
 
+#include "../xen.h"
 #include "../xen-compat.h"
 
+/* Some PV I/O interfaces need a compatibility variant. */
+#if __XEN_INTERFACE_VERSION__ < 0x00041300
+#define XENPV_FLEX_ARRAY_DIM  1 /* variable size */
+#else
+#define XENPV_FLEX_ARRAY_DIM  XEN_FLEX_ARRAY_DIM
+#endif
+
 #if __XEN_INTERFACE_VERSION__ < 0x00030208
 #define xen_mb()  mb()
 #define xen_rmb() rmb()
@@ -110,7 +118,7 @@  struct __name##_sring {                                                 \
         uint8_t pvt_pad[4];                                             \
     } pvt;                                                              \
     uint8_t __pad[44];                                                  \
-    union __name##_sring_entry ring[1]; /* variable-length */           \
+    union __name##_sring_entry ring[XENPV_FLEX_ARRAY_DIM];              \
 };                                                                      \
                                                                         \
 /* "Front" end's private variables */                                   \
@@ -479,7 +487,7 @@  struct name##_data_intf {                                                     \
     uint8_t pad2[56];                                                         \
                                                                               \
     RING_IDX ring_order;                                                      \
-    grant_ref_t ref[];                                                        \
+    grant_ref_t ref[XEN_FLEX_ARRAY_DIM];                                      \
 };                                                                            \
 DEFINE_XEN_FLEX_RING(name)
 
diff --git a/xen/include/public/io/sndif.h b/xen/include/public/io/sndif.h
index 4234a47c87..cce1459b7b 100644
--- a/xen/include/public/io/sndif.h
+++ b/xen/include/public/io/sndif.h
@@ -659,7 +659,7 @@  struct xensnd_open_req {
 
 struct xensnd_page_directory {
     grant_ref_t gref_dir_next_page;
-    grant_ref_t gref[1]; /* Variable length */
+    grant_ref_t gref[XENPV_FLEX_ARRAY_DIM];
 };
 
 /*
diff --git a/xen/include/public/xen-compat.h b/xen/include/public/xen-compat.h
index 97fe698498..078b796664 100644
--- a/xen/include/public/xen-compat.h
+++ b/xen/include/public/xen-compat.h
@@ -10,7 +10,7 @@ 
 #ifndef __XEN_PUBLIC_XEN_COMPAT_H__
 #define __XEN_PUBLIC_XEN_COMPAT_H__
 
-#define __XEN_LATEST_INTERFACE_VERSION__ 0x00040e00
+#define __XEN_LATEST_INTERFACE_VERSION__ 0x00041300
 
 #if defined(__XEN__) || defined(__XEN_TOOLS__)
 /* Xen is built with matching headers and implements the latest interface. */