[PATCH 10/17] dyndbg: replace classmap list with a vector

Jim Cromie
2026-05-04T20:45:30Z

Classmaps are stored in an elf section/array, but currently are
individually list-linked onto dyndbg's per-module ddebug_table for
operation. This is unnecessary.

Just like dyndbg's descriptors, classes are packed in compile order;
so even with many builtin modules employing multiple classmaps, each
modules' maps are packed contiguously, and can be treated as a
array-start-address & array-length.

So this drops the whole list building operation done in
ddebug_attach_module_classes(), and removes the list-head members.
The "select-by-modname" condition is reused to find the start,end of
the subrange.

NOTE: This "filter-by-modname" on classmaps should really be done in
ddebug_add_module(1); ie at least one step closer to ddebug_init(2),
which already splits up pr-debug descriptors into subranges by
modname, then calls (1) on each. (2) knows nothing of classmaps
currently, and doesn't need to. For now, just add comment.

Reviewed-by: Louis Chauvet <louis.chauvet@bootlin.com>
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
include/linux/dynamic_debug.h | 1 -
lib/dynamic_debug.c | 62 ++++++++++++++++++++++---------------------
2 files changed, 32 insertions(+), 31 deletions(-)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 92627a03b4d1..9fd36339db52 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -84,7 +84,6 @@ enum class_map_type {
};

struct ddebug_class_map {
- struct list_head link;
struct module *mod;
const char *mod_name; /* needed for builtins */
const char **class_names;
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index a18f4bc63473..94a66c8537ab 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -45,10 +45,11 @@ extern struct ddebug_class_map __start___dyndbg_classes[];
extern struct ddebug_class_map __stop___dyndbg_classes[];

struct ddebug_table {
- struct list_head link, maps;
+ struct list_head link;
const char *mod_name;
- unsigned int num_ddebugs;
struct _ddebug *ddebugs;
+ struct ddebug_class_map *classes;
+ unsigned int num_ddebugs, num_classes;
};

struct ddebug_query {
@@ -149,12 +150,13 @@ static void vpr_info_dq(const struct ddebug_query *query, const char *msg)
}

static struct ddebug_class_map *ddebug_find_valid_class(struct ddebug_table const *dt,
- const char *class_string, int *class_id)
+ const char *class_string,
+ int *class_id)
{
struct ddebug_class_map *map;
- int idx;
+ int i, idx;

- list_for_each_entry(map, &dt->maps, link) {
+ for (map = dt->classes, i = 0; i < dt->num_classes; i++, map++) {
idx = match_string(map->class_names, map->length, class_string);
if (idx >= 0) {
*class_id = idx + map->base;
@@ -165,7 +167,6 @@ static struct ddebug_class_map *ddebug_find_valid_class(struct ddebug_table cons
return NULL;
}

-#define __outvar /* filled by callee */
/*
* Search the tables for _ddebug's which match the given `query' and
* apply the `flags' and `mask' to them. Returns number of matching
@@ -227,7 +228,7 @@ static int ddebug_change(const struct ddebug_query *query,
unsigned int nfound = 0;
struct flagsbuf fbuf, nbuf;
struct ddebug_class_map *map = NULL;
- int __outvar valid_class;
+ int valid_class;

/* search for matching ddebugs */
mutex_lock(&ddebug_lock);
@@ -1134,9 +1135,10 @@ static void *ddebug_proc_next(struct seq_file *m, void *p, loff_t *pos)

static const char *ddebug_class_name(struct ddebug_iter *iter, struct _ddebug *dp)
{
- struct ddebug_class_map *map;
+ struct ddebug_class_map *map = iter->table->classes;
+ int i, nc = iter->table->num_classes;

- list_for_each_entry(map, &iter->table->maps, link)
+ for (i = 0; i < nc; i++, map++)
if (class_in_range(dp->class_id, map))
return map->class_names[dp->class_id - map->base];

@@ -1220,30 +1222,31 @@ static const struct proc_ops proc_fops = {
.proc_write = ddebug_proc_write
};

-static void ddebug_attach_module_classes(struct ddebug_table *dt,
- struct ddebug_class_map *classes,
- int num_classes)
+static void ddebug_attach_module_classes(struct ddebug_table *dt, struct _ddebug_info *di)
{
struct ddebug_class_map *cm;
- int i, j, ct = 0;
+ int i, nc = 0;

- for (cm = classes, i = 0; i < num_classes; i++, cm++) {
+ /*
+ * Find this module's classmaps in a subrange/wholerange of
+ * 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++) {

if (!strcmp(cm->mod_name, dt->mod_name)) {
-
- v2pr_info("class[%d]: module:%s base:%d len:%d ty:%d\n", i,
- cm->mod_name, cm->base, cm->length, cm->map_type);
-
- for (j = 0; j < cm->length; j++)
- v3pr_info(" %d: %d %s\n", j + cm->base, j,
- cm->class_names[j]);
-
- list_add(&cm->link, &dt->maps);
- ct++;
+ if (!nc) {
+ v2pr_info("start subrange, class[%d]: module:%s base:%d len:%d ty:%d\n",
+ i, cm->mod_name, cm->base, cm->length, cm->map_type);
+ dt->classes = cm;
+ }
+ nc++;
}
}
- if (ct)
- vpr_info("module:%s attached %d classes\n", dt->mod_name, ct);
+ if (nc) {
+ dt->num_classes = nc;
+ vpr_info("module:%s attached %d classes\n", dt->mod_name, nc);
+ }
}

/*
@@ -1275,10 +1278,9 @@ static int ddebug_add_module(struct _ddebug_info *di, const char *modname)
dt->num_ddebugs = di->num_descs;

INIT_LIST_HEAD(&dt->link);
- INIT_LIST_HEAD(&dt->maps);

if (di->classes && di->num_classes)
- ddebug_attach_module_classes(dt, di->classes, di->num_classes);
+ ddebug_attach_module_classes(dt, di);

mutex_lock(&ddebug_lock);
list_add_tail(&dt->link, &ddebug_tables);
@@ -1391,8 +1393,8 @@ static void ddebug_remove_all_tables(void)
mutex_lock(&ddebug_lock);
while (!list_empty(&ddebug_tables)) {
struct ddebug_table *dt = list_entry(ddebug_tables.next,
- struct ddebug_table,
- link);
+ struct ddebug_table,
+ link);
ddebug_table_free(dt);
}
mutex_unlock(&ddebug_lock);

--
2.54.0