[PATCH v6 14/31] dyndbg: macrofy a 2-index for-loop pattern

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

dynamic-debug currently has 2 __sections (__dyndbg, __dyndb_classes),
struct _ddebug_info keeps track of them both, with 2 members each:
_vec and _vec#_len.

We need to loop over these sections, with index and record pointer,
making ref to both _vec and _vec_len.  This is already fiddly and
error-prone, and will get worse as we add a 3rd section.

Lets instead embed/abstract the fiddly-ness in the `for_subvec()`
macro, and avoid repeating it going forward.

This is a for-loop macro expander, so it syntactically expects to
precede either a single statement or a { block } of them, and the
usual typeof or do-while-0 tricks are unavailable to fix the
multiple-expansion warning.

The macro needs a lot from its caller: it needs 2 local vars, 1 of
which is a ref to a contained struct with named members.  To support
these requirements, add:

1. __ASSERT_IS_LVALUE(_X):
   ie: ((void)sizeof((void)0, &(x)))

2. __ASSERT_HAS_VEC_MEMBERS(_X, _Y):
   compile-time check that the _Y "vector" exists
   ie: _X->_Y and _X->num##_Y are lvalues.

The for_subvec() macro then invokes these before the for-loop itself;
they disappear at runtime.  They do cause a "complex macro" CHECK from
checkpatch --strict.

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>

---
-v5+
  add __ASSERT_*() macros
  add then drop __chkp_no_side_effects() macro
  due to changes v5+ drop Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>

this patch evokes these complaints,
the "reuses" are all lvalues, so not issues.
(vec) is incompatible with ## paste-up
do-while also wont work here.

CHECK: Macro argument '_vec' may be better as '(_vec)' to avoid precedence issues
WARNING: Non-declarative macros with multiple statements should be enclosed in a do - while loop
CHECK: Macro argument reuse '_i' - possible side-effects?
CHECK: Macro argument reuse '_sp' - possible side-effects?
CHECK: Macro argument reuse '_box' - possible side-effects?
CHECK: Macro argument reuse '_vec' - possible side-effects?
---
 lib/dynamic_debug.c | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index e882e951d585..94d05d09a128 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -128,6 +128,28 @@ do {								\
 #define v3pr_info(fmt, ...)	vnpr_info(3, fmt, ##__VA_ARGS__)
 #define v4pr_info(fmt, ...)	vnpr_info(4, fmt, ##__VA_ARGS__)
 
+/*
+ * simplify a repeated for-loop pattern walking N steps in a T _vec
+ * member inside a struct _box.  It expects int i and T *_sp to be
+ * declared in the caller.
+ * @_i:  caller provided counter.
+ * @_sp: cursor into _vec, to examine each item.
+ * @_box: ptr to a struct containing @_vec member
+ * @_vec: name of a member in @_box
+ */
+#define __ASSERT_IS_LVALUE(x) ((void)sizeof((void)0, &(x)))
+#define __ASSERT_HAS_VEC_MEMBER(_box, _vec) ({	\
+	(void)sizeof((_box)->_vec);		\
+	(void)sizeof((_box)->num_##_vec);	\
+})
+#define for_subvec(_i, _sp, _box, _vec)			\
+	__ASSERT_IS_LVALUE(_i);				\
+	__ASSERT_IS_LVALUE(_sp);			\
+	__ASSERT_HAS_VEC_MEMBER(_box, _vec);		\
+	for ((_i) = 0, (_sp) = (_box)->_vec;		\
+	     (_i) < (_box)->num_##_vec;			\
+	     (_i)++, (_sp)++)
+
 static void vpr_info_dq(const struct ddebug_query *query, const char *msg)
 {
 	/* trim any trailing newlines */
@@ -155,7 +177,7 @@ static struct ddebug_class_map *ddebug_find_valid_class(struct ddebug_table cons
 	struct ddebug_class_map *map;
 	int i, idx;
 
-	for (map = dt->classes, i = 0; i < dt->num_classes; i++, map++) {
+	for_subvec(i, map, dt, classes) {
 		idx = match_string(map->class_names, map->length, class_string);
 		if (idx >= 0) {
 			*class_id = idx + map->base;
@@ -1231,8 +1253,7 @@ static void ddebug_attach_module_classes(struct ddebug_table *dt, struct _ddebug
 	 * the builtin/modular classmap vector/section.  Save the start
 	 * and length of the subrange at its edges.
 	 */
-	for (cm = di->classes, i = 0; i < di->num_classes; i++, cm++) {
-
+	for_subvec(i, cm, di, classes) {
 		if (!strcmp(cm->mod_name, dt->mod_name)) {
 			if (!nc) {
 				v2pr_info("start subrange, class[%d]: module:%s base:%d len:%d ty:%d\n",
-- 
2.51.1