linker-loader: Add new 'write pointer' command

This is similar to the existing 'add pointer' functionality, but instead
of instructing the guest (BIOS or UEFI) to patch memory, it instructs
the guest to write the pointer back to QEMU via a writeable fw_cfg file.

Signed-off-by: Ben Warren <ben@skyportsystems.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/acpi/bios-linker-loader.c

@@ -78,6 +78,21 @@ struct BiosLinkerLoaderEntry {
             uint32_t length;
         } cksum;
 
+        /*
+         * COMMAND_WRITE_POINTER - write the fw_cfg file (originating from
+         * @dest_file) at @wr_pointer.offset, by adding a pointer to
+         * @src_offset within the table originating from @src_file.
+         * 1,2,4 or 8 byte unsigned addition is used depending on
+         * @wr_pointer.size.
+         */
+        struct {
+            char dest_file[BIOS_LINKER_LOADER_FILESZ];
+            char src_file[BIOS_LINKER_LOADER_FILESZ];
+            uint32_t dst_offset;
+            uint32_t src_offset;
+            uint8_t size;
+        } wr_pointer;
+
         /* padding */
         char pad[124];
     };
@@ -85,9 +100,10 @@ struct BiosLinkerLoaderEntry {
 typedef struct BiosLinkerLoaderEntry BiosLinkerLoaderEntry;
 
 enum {
-    BIOS_LINKER_LOADER_COMMAND_ALLOCATE     = 0x1,
-    BIOS_LINKER_LOADER_COMMAND_ADD_POINTER  = 0x2,
-    BIOS_LINKER_LOADER_COMMAND_ADD_CHECKSUM = 0x3,
+    BIOS_LINKER_LOADER_COMMAND_ALLOCATE          = 0x1,
+    BIOS_LINKER_LOADER_COMMAND_ADD_POINTER       = 0x2,
+    BIOS_LINKER_LOADER_COMMAND_ADD_CHECKSUM      = 0x3,
+    BIOS_LINKER_LOADER_COMMAND_WRITE_POINTER     = 0x4,
 };
 
 enum {
@@ -278,3 +294,47 @@ void bios_linker_loader_add_pointer(BIOSLinker *linker,
 
     g_array_append_vals(linker->cmd_blob, &entry, sizeof entry);
 }
+
+/*
+ * bios_linker_loader_write_pointer: ask guest to write a pointer to the
+ * source file into the destination file, and write it back to QEMU via
+ * fw_cfg DMA.
+ *
+ * @linker: linker object instance
+ * @dest_file: destination file that must be written
+ * @dst_patched_offset: location within destination file blob to be patched
+ *                      with the pointer to @src_file, in bytes
+ * @dst_patched_offset_size: size of the pointer to be patched
+ *                      at @dst_patched_offset in @dest_file blob, in bytes
+ * @src_file: source file who's address must be taken
+ * @src_offset: location within source file blob to which
+ *              @dest_file+@dst_patched_offset will point to after
+ *              firmware's executed WRITE_POINTER command
+ */
+void bios_linker_loader_write_pointer(BIOSLinker *linker,
+                                    const char *dest_file,
+                                    uint32_t dst_patched_offset,
+                                    uint8_t dst_patched_size,
+                                    const char *src_file,
+                                    uint32_t src_offset)
+{
+    BiosLinkerLoaderEntry entry;
+    const BiosLinkerFileEntry *source_file =
+        bios_linker_find_file(linker, src_file);
+
+    assert(source_file);
+    assert(src_offset < source_file->blob->len);
+    memset(&entry, 0, sizeof entry);
+    strncpy(entry.wr_pointer.dest_file, dest_file,
+            sizeof entry.wr_pointer.dest_file - 1);
+    strncpy(entry.wr_pointer.src_file, src_file,
+            sizeof entry.wr_pointer.src_file - 1);
+    entry.command = cpu_to_le32(BIOS_LINKER_LOADER_COMMAND_WRITE_POINTER);
+    entry.wr_pointer.dst_offset = cpu_to_le32(dst_patched_offset);
+    entry.wr_pointer.src_offset = cpu_to_le32(src_offset);
+    entry.wr_pointer.size = dst_patched_size;
+    assert(dst_patched_size == 1 || dst_patched_size == 2 ||
+           dst_patched_size == 4 || dst_patched_size == 8);
+
+    g_array_append_vals(linker->cmd_blob, &entry, sizeof entry);
+}

include/hw/acpi/bios-linker-loader.h

@@ -26,5 +26,12 @@ void bios_linker_loader_add_pointer(BIOSLinker *linker,
                                     const char *src_file,
                                     uint32_t src_offset);
 
+void bios_linker_loader_write_pointer(BIOSLinker *linker,
+                                      const char *dest_file,
+                                      uint32_t dst_patched_offset,
+                                      uint8_t dst_patched_size,
+                                      const char *src_file,
+                                      uint32_t src_offset);
+
 void bios_linker_loader_cleanup(BIOSLinker *linker);
 #endif