[Xen-devel] [PATCH v4 1/4] x86/HVM: update the start info structure layout

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

After some discussion around the new boot ABI consensus has been reached
about the layout and contents of the start info. The following patch updates
the layout to what has been agreed.

Also, the new layout is described in binary terms in order to avoid issues
with alignments when using C structs.

Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
---
Cc: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>
Cc: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 tools/libxc/include/xc_dom.h | 31 +++++++++++++++++++++++++
 xen/include/public/xen.h     | 55 ++++++++++++++++++++++++++++++--------------
 2 files changed, 69 insertions(+), 17 deletions(-)

diff --git a/tools/libxc/include/xc_dom.h b/tools/libxc/include/xc_dom.h
index cac4698..6ebe946 100644
--- a/tools/libxc/include/xc_dom.h
+++ b/tools/libxc/include/xc_dom.h
@@ -216,6 +216,37 @@ struct xc_dom_image {
     struct xc_hvm_firmware_module smbios_module;
 };
 
+#if defined(__i386__) || defined(__x86_64__)
+/* C representation of the x86/HVM start info layout.
+ *
+ * The canonical definition of this layout resides in public/xen.h, this
+ * is just a way to represent the layout described there using C types.
+ *
+ * NB: the packed attribute is not really needed, but it helps us enforce
+ * the fact this this is just a representation, and it might indeed
+ * be required in the future if there are alignment changes.
+ */
+struct hvm_start_info {
+    uint32_t magic;             /* Contains the magic value 0x336ec578       */
+                                /* ("xEn3" with the 0x80 bit of the "E" set).*/
+    uint32_t version;           /* Version of this structure.                */
+    uint32_t flags;             /* SIF_xxx flags.                            */
+    uint32_t cmdline_paddr;     /* Physical address of the command line.     */
+    uint32_t nr_modules;        /* Number of modules passed to the kernel.   */
+    uint32_t modlist_paddr;     /* Physical address of an array of           */
+                                /* hvm_modlist_entry.                        */
+    uint32_t rsdp_paddr;        /* Physical address of the RSDP ACPI data    */
+                                /* structure.                                */
+} __attribute__((packed));
+
+struct hvm_modlist_entry {
+    uint64_t paddr;             /* Physical address of the module.           */
+    uint64_t size;              /* Size of the module in bytes.              */
+    uint64_t cmdline_paddr;     /* Physical address of the command line.     */
+    uint64_t reserved;
+} __attribute__((packed));
+#endif /* x86 */
+
 /* --- pluggable kernel loader ------------------------------------- */
 
 struct xc_dom_loader {
diff --git a/xen/include/public/xen.h b/xen/include/public/xen.h
index 7b629b1..6ba060f 100644
--- a/xen/include/public/xen.h
+++ b/xen/include/public/xen.h
@@ -787,25 +787,46 @@ typedef struct start_info start_info_t;
 /*
  * Start of day structure passed to PVH guests in %ebx.
  *
- * NOTE: nothing will be loaded at physical address 0, so
- * a 0 value in any of the address fields should be treated
- * as not present.
+ * NOTE: nothing will be loaded at physical address 0, so a 0 value in any
+ * of the address fields should be treated as not present.
+ *
+ *  0 +----------------+
+ *    | magic          | Contains the magic value HVM_START_MAGIC_VALUE
+ *    |                | ("xEn3" with the 0x80 bit of the "E" set).
+ *  4 +----------------+
+ *    | version        | Version of this structure. Current version is 0. New
+ *    |                | versions are guaranteed to be backwards-compatible.
+ *  8 +----------------+
+ *    | flags          | SIF_xxx flags.
+ * 12 +----------------+
+ *    | cmdline_paddr  | Physical address of the command line,
+ *    |                | a zero-terminated ASCII string.
+ * 16 +----------------+
+ *    | nr_modules     | Number of modules passed to the kernel.
+ * 20 +----------------+
+ *    | modlist_paddr  | Physical address of an array of modules
+ *    |                | (layout of the structure below).
+ * 24 +----------------+
+ *    | rsdp_paddr     | Physical address of the RSDP ACPI data structure.
+ * 28 +----------------+
+ *
+ * The layout of each entry in the module structure is the following:
+ *
+ *  0 +----------------+
+ *    | paddr          | Physical address of the module.
+ *  8 +----------------+
+ *    | size           | Size of the module in bytes.
+ * 16 +----------------+
+ *    | cmdline_paddr  | Physical address of the command line,
+ *    |                | a zero-terminated ASCII string.
+ * 24 +----------------+
+ *    | reserved       |
+ * 32 +----------------+
+ *
+ * The address and size of the modules is a 64bit unsigned integer. However
+ * Xen will always try to place all modules below the 4GiB boundary.
  */
-struct hvm_start_info {
 #define HVM_START_MAGIC_VALUE 0x336ec578
-    uint32_t magic;             /* Contains the magic value 0x336ec578       */
-                                /* ("xEn3" with the 0x80 bit of the "E" set).*/
-    uint32_t flags;             /* SIF_xxx flags.                            */
-    uint32_t cmdline_paddr;     /* Physical address of the command line.     */
-    uint32_t nr_modules;        /* Number of modules passed to the kernel.   */
-    uint32_t modlist_paddr;     /* Physical address of an array of           */
-                                /* hvm_modlist_entry.                        */
-};
-
-struct hvm_modlist_entry {
-    uint32_t paddr;             /* Physical address of the module.           */
-    uint32_t size;              /* Size of the module in bytes.              */
-};
 
 /* New console union for dom0 introduced in 0x00030203. */
 #if __XEN_INTERFACE_VERSION__ < 0x00030203
-- 
2.5.4 (Apple Git-61)


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