common: Define markers for weak symbols

This patch introduces macros to mark weak symbols. These macros are
used to annotate weak definitions, declarations, and overriding
definitions.

__override_proto: declarations
__override: definitions which take precedence
__overridable: default (weak) definitions

Signed-off-by: Daisuke Nojiri <dnojiri@chromium.org>

BUG=chromium.org/964060
BRANCH=none
TEST=buildall

Change-Id: I44cec41e0523e285db19a890d084b52337f64a9c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1633911
Reviewed-by: Jack Rosenthal <jrosenth@chromium.org>
Reviewed-by: Denis Brockus <dbrockus@chromium.org>
Reviewed-by: Jett Rink <jettrink@chromium.org>
Tested-by: Jack Rosenthal <jrosenth@chromium.org>
Commit-Queue: Denis Brockus <dbrockus@chromium.org>

1 files changed, 27 insertions, 0 deletions

diff --git a/include/common.h b/include/common.h
index 388d3f413f..1f01652909 100644
--- a/include/common.h
+++ b/include/common.h
@@ -232,6 +232,33 @@ enum ec_error_list {
 #endif
 
 /*
+ * Weak symbol markers
+ *
+ * These macros are used to annotate weak definitions, their declarations, and
+ * overriding definitions.
+ *
+ * __override_proto: declarations
+ * __override: definitions which take precedence
+ * __overridable: default (weak) definitions
+ *
+ * For example, in foo.h:
+ *   __override_proto void foo(void);
+ *
+ * and in foo.c:
+ *   __overridable void foo(void) {
+ *     ...
+ *   }
+ *
+ * and in board.c:
+ *   __override void foo(void) {
+ *     ...
+ *   }
+ */
+#define __override_proto
+#define __override
+#define __overridable	__attribute__((weak))
+
+/*
  * Mark functions that collide with stdlib so they can be hidden when linking
  * against libraries that require stdlib. HIDE_EC_STDLIB should be defined
  * before including common.h from code that links to cstdlib.