Add basic infrastructure to support code tagging which stores tag common
information consisting of the module name, function, file name and line
number. Provide functions to register a new code tag type and navigate
between code tags.

Co-developed-by: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 include/linux/codetag.h |  71 ++++++++++++++
 lib/Kconfig.debug       |   4 +
 lib/Makefile            |   1 +
 lib/codetag.c           | 199 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 275 insertions(+)
 create mode 100644 include/linux/codetag.h
 create mode 100644 lib/codetag.c

diff --git a/include/linux/codetag.h b/include/linux/codetag.h
new file mode 100644
index 000000000000..a9d7adecc2a5
--- /dev/null
+++ b/include/linux/codetag.h

@@ -0,0 +1,71 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * code tagging framework
+ */
+#ifndef _LINUX_CODETAG_H
+#define _LINUX_CODETAG_H
+
+#include <linux/types.h>
+
+struct codetag_iterator;
+struct codetag_type;
+struct seq_buf;
+struct module;
+
+/*
+ * An instance of this structure is created in a special ELF section at every
+ * code location being tagged.  At runtime, the special section is treated as
+ * an array of these.
+ */
+struct codetag {
+	unsigned int flags; /* used in later patches */
+	unsigned int lineno;
+	const char *modname;
+	const char *function;
+	const char *filename;
+} __aligned(8);
+
+union codetag_ref {
+	struct codetag *ct;
+};
+
+struct codetag_range {
+	struct codetag *start;
+	struct codetag *stop;
+};
+
+struct codetag_module {
+	struct module *mod;
+	struct codetag_range range;
+};
+
+struct codetag_type_desc {
+	const char *section;
+	size_t tag_size;
+};
+
+struct codetag_iterator {
+	struct codetag_type *cttype;
+	struct codetag_module *cmod;
+	unsigned long mod_id;
+	struct codetag *ct;
+};
+
+#define CODE_TAG_INIT {					\
+	.modname	= KBUILD_MODNAME,		\
+	.function	= __func__,			\
+	.filename	= __FILE__,			\
+	.lineno		= __LINE__,			\
+	.flags		= 0,				\
+}
+
+void codetag_lock_module_list(struct codetag_type *cttype, bool lock);
+struct codetag_iterator codetag_get_ct_iter(struct codetag_type *cttype);
+struct codetag *codetag_next_ct(struct codetag_iterator *iter);
+
+void codetag_to_text(struct seq_buf *out, struct codetag *ct);
+
+struct codetag_type *
+codetag_register_type(const struct codetag_type_desc *desc);
+
+#endif /* _LINUX_CODETAG_H */

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 975a07f9f1cc..0be2d00c3696 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug

@@ -968,6 +968,10 @@ config DEBUG_STACKOVERFLOW
 
 	  If in doubt, say "N".
 
+config CODE_TAGGING
+	bool
+	select KALLSYMS
+
 source "lib/Kconfig.kasan"
 source "lib/Kconfig.kfence"
 source "lib/Kconfig.kmsan"

diff --git a/lib/Makefile b/lib/Makefile
index 6b09731d8e61..6b48b22fdfac 100644
--- a/lib/Makefile
+++ b/lib/Makefile

@@ -235,6 +235,7 @@ obj-$(CONFIG_OF_RECONFIG_NOTIFIER_ERROR_INJECT) += \
 	of-reconfig-notifier-error-inject.o
 obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
 
+obj-$(CONFIG_CODE_TAGGING) += codetag.o
 lib-$(CONFIG_GENERIC_BUG) += bug.o
 
 obj-$(CONFIG_HAVE_ARCH_TRACEHOOK) += syscall.o

diff --git a/lib/codetag.c b/lib/codetag.c
new file mode 100644
index 000000000000..7708f8388e55
--- /dev/null
+++ b/lib/codetag.c

@@ -0,0 +1,199 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/codetag.h>
+#include <linux/idr.h>
+#include <linux/kallsyms.h>
+#include <linux/module.h>
+#include <linux/seq_buf.h>
+#include <linux/slab.h>
+
+struct codetag_type {
+	struct list_head link;
+	unsigned int count;
+	struct idr mod_idr;
+	struct rw_semaphore mod_lock; /* protects mod_idr */
+	struct codetag_type_desc desc;
+};
+
+static DEFINE_MUTEX(codetag_lock);
+static LIST_HEAD(codetag_types);
+
+void codetag_lock_module_list(struct codetag_type *cttype, bool lock)
+{
+	if (lock)
+		down_read(&cttype->mod_lock);
+	else
+		up_read(&cttype->mod_lock);
+}
+
+struct codetag_iterator codetag_get_ct_iter(struct codetag_type *cttype)
+{
+	struct codetag_iterator iter = {
+		.cttype = cttype,
+		.cmod = NULL,
+		.mod_id = 0,
+		.ct = NULL,
+	};
+
+	return iter;
+}
+
+static inline struct codetag *get_first_module_ct(struct codetag_module *cmod)
+{
+	return cmod->range.start < cmod->range.stop ? cmod->range.start : NULL;
+}
+
+static inline
+struct codetag *get_next_module_ct(struct codetag_iterator *iter)
+{
+	struct codetag *res = (struct codetag *)
+			((char *)iter->ct + iter->cttype->desc.tag_size);
+
+	return res < iter->cmod->range.stop ? res : NULL;
+}
+
+struct codetag *codetag_next_ct(struct codetag_iterator *iter)
+{
+	struct codetag_type *cttype = iter->cttype;
+	struct codetag_module *cmod;
+	struct codetag *ct;
+
+	lockdep_assert_held(&cttype->mod_lock);
+
+	if (unlikely(idr_is_empty(&cttype->mod_idr)))
+		return NULL;
+
+	ct = NULL;
+	while (true) {
+		cmod = idr_find(&cttype->mod_idr, iter->mod_id);
+
+		/* If module was removed move to the next one */
+		if (!cmod)
+			cmod = idr_get_next_ul(&cttype->mod_idr,
+					       &iter->mod_id);
+
+		/* Exit if no more modules */
+		if (!cmod)
+			break;
+
+		if (cmod != iter->cmod) {
+			iter->cmod = cmod;
+			ct = get_first_module_ct(cmod);
+		} else
+			ct = get_next_module_ct(iter);
+
+		if (ct)
+			break;
+
+		iter->mod_id++;
+	}
+
+	iter->ct = ct;
+	return ct;
+}
+
+void codetag_to_text(struct seq_buf *out, struct codetag *ct)
+{
+	seq_buf_printf(out, "%s:%u module:%s func:%s",
+		       ct->filename, ct->lineno,
+		       ct->modname, ct->function);
+}