[PATCH v6 30/31] dyndbg: add DYNAMIC_DEBUG_CLASSMAP_USE_(dd_class_name, offset)

[Jim Cromie <jim.cromie@gmail.com>]

Allow a module to use 2 classmaps together that would otherwise have a
class_id range conflict.

Suppose drm-driver does:

  DYNAMIC_DEBUG_CLASSMAP_USE(drm_debug_classes);
  DYNAMIC_DEBUG_CLASSMAP_USE(drm_accel_xfer_debug);

And (for some reason) drm-accel will not define their constants to
avoid DRM's 0..10 reservations (seems a long stretch).

So I dont think this potential conflict would become an issue until we
have at least a 3-X-3 of classmap-defns X classmap-users

So drop this if its too speculative, knowing theres at least a
notional solution should the situation arise.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
re-ref of an lvalue is fine.
CHECK: Macro argument reuse '_var' - possible side-effects?

-v5+ less hand-wavy
---
 include/linux/dynamic_debug.h | 30 +++++++++++++++++++++++-------
 lib/dynamic_debug.c           | 19 ++++++++++++-------
 2 files changed, 35 insertions(+), 14 deletions(-)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index b22da40e2583..5307be8da5c1 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -87,7 +87,7 @@ struct _ddebug_class_map {
 struct _ddebug_class_user {
 	char *mod_name;
 	struct _ddebug_class_map *map;
-	const int base;		/* user offset to re-number the used map */
+	const int offset;	/* offset from map->base */
 };
 
 /*
@@ -235,21 +235,37 @@ struct _ddebug_class_param {
 /**
  * DYNAMIC_DEBUG_CLASSMAP_USE - refer to a classmap, DEFINEd elsewhere.
  * @_var: name of the exported classmap var
- * @_not_yet: _base-like, but applies only to this USEr. (if needed)
  *
  * This tells dyndbg that the module has prdbgs with classids defined
  * in the named classmap.  This qualifies "class NAME" >controls on
- * the user module, and ignores unknown names.
+ * the user module, and ignores unknown names. This is a wrapper for
+ * DYNAMIC_DEBUG_CLASSMAP_USE_() with a base offset of 0.
  */
-#define DYNAMIC_DEBUG_CLASSMAP_USE(_var)				\
-	DYNAMIC_DEBUG_CLASSMAP_USE_(_var, 0, __UNIQUE_ID(_ddebug_class_user))
-#define DYNAMIC_DEBUG_CLASSMAP_USE_(_var, _base, _uname)		\
+#define DYNAMIC_DEBUG_CLASSMAP_USE(_var) \
+	DYNAMIC_DEBUG_CLASSMAP_USE_(_var, 0)
+
+/**
+ * DYNAMIC_DEBUG_CLASSMAP_USE_ - refer to a classmap with a manual offset.
+ * @_var:   name of the exported classmap var to use.
+ * @_offset:  an integer offset to add to the class IDs of the used map.
+ *
+ * This is an extended version of DYNAMIC_DEBUG_CLASSMAP_USE(). It should
+ * only be used to resolve class ID conflicts when a module uses multiple
+ * classmaps that have overlapping ID ranges.
+ *
+ * The final class IDs for the used map will be calculated as:
+ * original_map_base + class_index + @_base.
+ */
+#define DYNAMIC_DEBUG_CLASSMAP_USE_(_var, _offset)			\
+	__DYNAMIC_DEBUG_CLASSMAP_USE(_var, _offset, __UNIQUE_ID(_ddebug_class_user))
+
+#define __DYNAMIC_DEBUG_CLASSMAP_USE(_var, _offset, _uname)		\
 	extern struct _ddebug_class_map _var;				\
 	static struct _ddebug_class_user __aligned(8) __used		\
 	__section("__dyndbg_class_users") _uname = {			\
 		.mod_name = KBUILD_MODNAME,				\
 		.map = &(_var),						\
-		.base = _base						\
+		.offset = _offset						\
 	}
 
 /**
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 1082e0273f0e..bf1ff29cca95 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -198,7 +198,7 @@ ddebug_find_valid_class(struct _ddebug_info const *di, const char *query_class,
 		if (idx >= 0) {
 			vpr_di_info(di, "class-ref: %s -> %s.%s ",
 				    cli->mod_name, cli->map->mod_name, query_class);
-			*class_id = idx + cli->map->base;
+			*class_id = idx + cli->map->base - cli->offset;
 			return cli->map;
 		}
 	}
@@ -206,12 +206,17 @@ ddebug_find_valid_class(struct _ddebug_info const *di, const char *query_class,
 	return NULL;
 }
 
-static bool ddebug_class_in_range(const int class_id, const struct _ddebug_class_map *map)
+static bool ddebug_class_map_in_range(const int class_id, const struct _ddebug_class_map *map)
 {
 	return (class_id >= map->base &&
 		class_id < map->base + map->length);
 }
 
+static bool ddebug_class_user_in_range(const int class_id, const struct _ddebug_class_user *user)
+{
+	return ddebug_class_map_in_range(class_id - user->offset, user->map);
+}
+
 static struct _ddebug_class_map *
 ddebug_find_map_by_class_id(struct _ddebug_info *di, int class_id)
 {
@@ -220,11 +225,11 @@ ddebug_find_map_by_class_id(struct _ddebug_info *di, int class_id)
 	int i;
 
 	for_subvec(i, map, di, maps)
-		if (ddebug_class_in_range(class_id, map))
+		if (ddebug_class_map_in_range(class_id, map))
 			return map;
 
 	for_subvec(i, cli, di, users)
-		if (ddebug_class_in_range(class_id, cli->map))
+		if (ddebug_class_user_in_range(class_id, cli))
 			return cli->map;
 
 	return NULL;
@@ -1177,12 +1182,12 @@ static const char *ddebug_class_name(struct _ddebug_info *di, struct _ddebug *dp
 	int i;
 
 	for_subvec(i, map, di, maps)
-		if (ddebug_class_in_range(dp->class_id, map))
+		if (ddebug_class_map_in_range(dp->class_id, map))
 			return map->class_names[dp->class_id - map->base];
 
 	for_subvec(i, cli, di, users)
-		if (ddebug_class_in_range(dp->class_id, cli->map))
-			return cli->map->class_names[dp->class_id - cli->map->base];
+		if (ddebug_class_user_in_range(dp->class_id, cli))
+			return cli->map->class_names[dp->class_id - cli->map->base - cli->offset];
 
 	return NULL;
 }
-- 
2.51.1