1 files changed, 89 insertions, 8 deletions

diff --git a/qemu/hw/acpi/bios-linker-loader.c b/qemu/hw/acpi/bios-linker-loader.c
index d9382f826..5153ab151 100644
--- a/qemu/hw/acpi/bios-linker-loader.c
+++ b/qemu/hw/acpi/bios-linker-loader.c
@@ -18,12 +18,20 @@
  * with this program; if not, see <http://www.gnu.org/licenses/>.
  */
 
+#include "qemu/osdep.h"
 #include "qemu-common.h"
 #include "hw/acpi/bios-linker-loader.h"
 #include "hw/nvram/fw_cfg.h"
 
 #include "qemu/bswap.h"
 
+/*
+ * Linker/loader is a paravirtualized interface that passes commands to guest.
+ * The commands can be used to request guest to
+ * - allocate memory chunks and initialize them from QEMU FW CFG files
+ * - link allocated chunks by storing pointer to one chunk into another
+ * - calculate ACPI checksum of part of the chunk and store into same chunk
+ */
 #define BIOS_LINKER_LOADER_FILESZ FW_CFG_MAX_FILE_PATH
 
 struct BiosLinkerLoaderEntry {
@@ -87,6 +95,12 @@ enum {
     BIOS_LINKER_LOADER_ALLOC_ZONE_FSEG = 0x2,
 };
 
+/*
+ * bios_linker_loader_init: allocate a new linker file blob array.
+ *
+ * After initialization, linker commands can be added, and will
+ * be stored in the array.
+ */
 GArray *bios_linker_loader_init(void)
 {
     return g_array_new(false, true /* clear */, 1);
@@ -98,6 +112,16 @@ void *bios_linker_loader_cleanup(GArray *linker)
     return g_array_free(linker, false);
 }
 
+/*
+ * bios_linker_loader_alloc: ask guest to load file into guest memory.
+ *
+ * @linker: linker file blob array
+ * @file: file to be loaded
+ * @alloc_align: required minimal alignment in bytes. Must be a power of 2.
+ * @alloc_fseg: request allocation in FSEG zone (useful for the RSDP ACPI table)
+ *
+ * Note: this command must precede any other linker command using this file.
+ */
 void bios_linker_loader_alloc(GArray *linker,
                               const char *file,
                               uint32_t alloc_align,
@@ -105,35 +129,90 @@ void bios_linker_loader_alloc(GArray *linker,
 {
     BiosLinkerLoaderEntry entry;
 
+    assert(!(alloc_align & (alloc_align - 1)));
+
     memset(&entry, 0, sizeof entry);
     strncpy(entry.alloc.file, file, sizeof entry.alloc.file - 1);
     entry.command = cpu_to_le32(BIOS_LINKER_LOADER_COMMAND_ALLOCATE);
     entry.alloc.align = cpu_to_le32(alloc_align);
-    entry.alloc.zone = cpu_to_le32(alloc_fseg ?
-                                    BIOS_LINKER_LOADER_ALLOC_ZONE_FSEG :
-                                    BIOS_LINKER_LOADER_ALLOC_ZONE_HIGH);
+    entry.alloc.zone = alloc_fseg ? BIOS_LINKER_LOADER_ALLOC_ZONE_FSEG :
+                                    BIOS_LINKER_LOADER_ALLOC_ZONE_HIGH;
 
     /* Alloc entries must come first, so prepend them */
     g_array_prepend_vals(linker, &entry, sizeof entry);
 }
 
+/*
+ * bios_linker_loader_add_checksum: ask guest to add checksum of file data
+ * into (same) file at the specified pointer.
+ *
+ * Checksum calculation simply sums -X for each byte X in the range
+ * using 8-bit math (i.e. ACPI checksum).
+ *
+ * @linker: linker file blob array
+ * @file: file that includes the checksum to be calculated
+ *        and the data to be checksummed
+ * @table: @file blob contents
+ * @start, @size: range of data to checksum
+ * @checksum: location of the checksum to be patched within file blob
+ *
+ * Notes:
+ * - checksum byte initial value must have been pushed into @table
+ *   and reside at address @checksum.
+ * - @size bytes must have been pushed into @table and reside at address
+ *   @start.
+ * - Guest calculates checksum of specified range of data, result is added to
+ *   initial value at @checksum into copy of @file in Guest memory.
+ * - Range might include the checksum itself.
+ * - To avoid confusion, caller must always put 0x0 at @checksum.
+ * - @file must be loaded into Guest memory using bios_linker_loader_alloc
+ */
 void bios_linker_loader_add_checksum(GArray *linker, const char *file,
-                                     void *table,
+                                     GArray *table,
                                      void *start, unsigned size,
                                      uint8_t *checksum)
 {
     BiosLinkerLoaderEntry entry;
+    ptrdiff_t checksum_offset = (gchar *)checksum - table->data;
+    ptrdiff_t start_offset = (gchar *)start - table->data;
+
+    assert(checksum_offset >= 0);
+    assert(start_offset >= 0);
+    assert(checksum_offset + 1 <= table->len);
+    assert(start_offset + size <= table->len);
+    assert(*checksum == 0x0);
 
     memset(&entry, 0, sizeof entry);
     strncpy(entry.cksum.file, file, sizeof entry.cksum.file - 1);
     entry.command = cpu_to_le32(BIOS_LINKER_LOADER_COMMAND_ADD_CHECKSUM);
-    entry.cksum.offset = cpu_to_le32(checksum - (uint8_t *)table);
-    entry.cksum.start = cpu_to_le32((uint8_t *)start - (uint8_t *)table);
+    entry.cksum.offset = cpu_to_le32(checksum_offset);
+    entry.cksum.start = cpu_to_le32(start_offset);
     entry.cksum.length = cpu_to_le32(size);
 
     g_array_append_vals(linker, &entry, sizeof entry);
 }
 
+/*
+ * bios_linker_loader_add_pointer: ask guest to add address of source file
+ * into destination file at the specified pointer.
+ *
+ * @linker: linker file blob array
+ * @dest_file: destination file that must be changed
+ * @src_file: source file who's address must be taken
+ * @table: @dest_file blob contents array
+ * @pointer: location of the pointer to be patched within destination file blob
+ * @pointer_size: size of pointer to be patched, in bytes
+ *
+ * Notes:
+ * - @pointer_size bytes must have been pushed into @table
+ *   and reside at address @pointer.
+ * - Guest address is added to initial value at @pointer
+ *   into copy of @dest_file in Guest memory.
+ *   e.g. to get start of src_file in guest memory, put 0x0 there
+ *   to get address of a field at offset 0x10 in src_file, put 0x10 there
+ * - Both @dest_file and @src_file must be
+ *   loaded into Guest memory using bios_linker_loader_alloc
+ */
 void bios_linker_loader_add_pointer(GArray *linker,
                                     const char *dest_file,
                                     const char *src_file,
@@ -141,7 +220,10 @@ void bios_linker_loader_add_pointer(GArray *linker,
                                     uint8_t pointer_size)
 {
     BiosLinkerLoaderEntry entry;
-    size_t offset = (gchar *)pointer - table->data;
+    ptrdiff_t offset = (gchar *)pointer - table->data;
+
+    assert(offset >= 0);
+    assert(offset + pointer_size <= table->len);
 
     memset(&entry, 0, sizeof entry);
     strncpy(entry.pointer.dest_file, dest_file,
@@ -149,7 +231,6 @@ void bios_linker_loader_add_pointer(GArray *linker,
     strncpy(entry.pointer.src_file, src_file,
             sizeof entry.pointer.src_file - 1);
     entry.command = cpu_to_le32(BIOS_LINKER_LOADER_COMMAND_ADD_POINTER);
-    assert(table->len >= offset + pointer_size);
     entry.pointer.offset = cpu_to_le32(offset);
     entry.pointer.size = pointer_size;
     assert(pointer_size == 1 || pointer_size == 2 ||