kpatch-build: let locals_match to match 90% of local symbols

With clang PGO is used, the compiler uses function signature to match
functions to profile data. When the signature of a function changed as
part of livepatch, the profile data is ignore. This may cause the compiler
to make different inline decisions, and thus cause mismatch in local
functions.

To adapt to this case, let locals_match to count the number of match and
mismatch symbols. If 90% of the symbols match, we consider the two files
are the same.

Signed-off-by: Song Liu <song@kernel.org>

Author: liu-song-6

kpatch-build/lookup.c

@@ -91,11 +91,13 @@ static bool maybe_discarded_sym(const char *name)
 }
 
 static bool locals_match(struct lookup_table *table, int idx,
-			struct symbol *file_sym, struct list_head *sym_list)
+			 struct symbol *file_sym, struct list_head *sym_list,
+			 int match_pct)
 {
 	struct symbol *sym;
 	struct object_symbol *table_sym;
 	int i, found;
+	int match_cnt = 0, mismatch_cnt = 0;
 
 	i = idx + 1;
 	for_each_obj_symbol_continue(i, table_sym, table) {
@@ -121,10 +123,18 @@ static bool locals_match(struct lookup_table *table, int idx,
 			}
 		}
 
-		if (!found)
-			return false;
+		if (found)
+			match_cnt++;
+		else
+			mismatch_cnt++;
 	}
 
+	if (match_cnt * 100 < (match_cnt + mismatch_cnt) * match_pct)
+		return false;
+
+	match_cnt = 0;
+	mismatch_cnt = 0;
+
 	sym = file_sym;
 	list_for_each_entry_continue(sym, sym_list, list) {
 		if (sym->type == STT_FILE)
@@ -157,11 +167,13 @@ static bool locals_match(struct lookup_table *table, int idx,
 			}
 		}
 
-		if (!found)
-			return false;
+		if (found)
+			match_cnt++;
+		else
+			mismatch_cnt++;
 	}
 
-	return true;
+	return match_cnt * 100 >= (match_cnt + mismatch_cnt) * match_pct;
 }
 
 static void find_local_syms(struct lookup_table *table, struct symbol *file_sym,
@@ -176,7 +188,7 @@ static void find_local_syms(struct lookup_table *table, struct symbol *file_sym,
 			continue;
 		if (strcmp(file_sym->name, sym->name))
 			continue;
-		if (!locals_match(table, i, file_sym, sym_list))
+		if (!locals_match(table, i, file_sym, sym_list, 90 /* match_pct */))
 			continue;
 		if (lookup_table_file_sym)
 			ERROR("found duplicate matches for %s local symbols in %s symbol table",