gcov: support GCC 12.1 and newer compilers

Starting with GCC 12.1, the created .gcda format can't be read by gcov
tool.  There are 2 significant changes to the .gcda file format that
need to be supported:

a) [gcov: Use system IO buffering]
   (23eb66d1d46a34cb28c4acbdf8a1deb80a7c5a05) changed that all sizes in
   the format are in bytes and not in words (4B)

b) [gcov: make profile merging smarter]
   (72e0c742bd01f8e7e6dcca64042b9ad7e75979de) add a new checksum to the
   file header.

Tested with GCC 7.5, 10.4, 12.2 and the current master.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Martin Liska <[email protected]>
Tested-by: Peter Oberparleiter <[email protected]>
Reviewed-by: Peter Oberparleiter <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

kernel/gcov/gcc_4_7.c

@@ -30,6 +30,13 @@
 
 #define GCOV_TAG_FUNCTION_LENGTH 3
 
+/* Since GCC 12.1 sizes are in BYTES and not in WORDS (4B). */
+#if (__GNUC__ >= 12)
+#define GCOV_UNIT_SIZE 4
+#else
+#define GCOV_UNIT_SIZE 1
+#endif
+
 static struct gcov_info *gcov_info_head;
 
 /**
@@ -383,12 +390,18 @@ size_t convert_to_gcda(char *buffer, struct gcov_info *info)
  pos += store_gcov_u32(buffer, pos, info->version);
  pos += store_gcov_u32(buffer, pos, info->stamp);
 
+#if (__GNUC__ >= 12)
+ /* Use zero as checksum of the compilation unit. */
+ pos += store_gcov_u32(buffer, pos, 0);
+#endif
+
  for (fi_idx = 0; fi_idx < info->n_functions; fi_idx++) {
  fi_ptr = info->functions[fi_idx];
 
  /* Function record. */
  pos += store_gcov_u32(buffer, pos, GCOV_TAG_FUNCTION);
- pos += store_gcov_u32(buffer, pos, GCOV_TAG_FUNCTION_LENGTH);
+ pos += store_gcov_u32(buffer, pos,
+ GCOV_TAG_FUNCTION_LENGTH * GCOV_UNIT_SIZE);
  pos += store_gcov_u32(buffer, pos, fi_ptr->ident);
  pos += store_gcov_u32(buffer, pos, fi_ptr->lineno_checksum);
  pos += store_gcov_u32(buffer, pos, fi_ptr->cfg_checksum);
@@ -402,7 +415,8 @@ size_t convert_to_gcda(char *buffer, struct gcov_info *info)
  /* Counter record. */
  pos += store_gcov_u32(buffer, pos,
  GCOV_TAG_FOR_COUNTER(ct_idx));
- pos += store_gcov_u32(buffer, pos, ci_ptr->num * 2);
+ pos += store_gcov_u32(buffer, pos,
+ ci_ptr->num * 2 * GCOV_UNIT_SIZE);
 
  for (cv_idx = 0; cv_idx < ci_ptr->num; cv_idx++) {
  pos += store_gcov_u64(buffer, pos,