bug: Add report_bug_entry()

Add a report_bug() variant where the bug_entry is already known. This
is useful when the exception instruction is not instantiated per-site.
But instead has a single instance. In such a case the bug_entry
address might be passed along in a known register or something.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251110115757.575795595@infradead.org

Author: Peter Zijlstra

include/linux/bug.h

@@ -42,6 +42,7 @@ void bug_get_file_line(struct bug_entry *bug, const char **file,
 struct bug_entry *find_bug(unsigned long bugaddr);
 
 enum bug_trap_type report_bug(unsigned long bug_addr, struct pt_regs *regs);
+enum bug_trap_type report_bug_entry(struct bug_entry *bug, struct pt_regs *regs);
 
 /* These are defined by the architecture */
 int is_valid_bugaddr(unsigned long addr);
@@ -62,6 +63,13 @@ static inline enum bug_trap_type report_bug(unsigned long bug_addr,
 }
 
 struct bug_entry;
+
+static inline enum bug_trap_type
+report_bug_entry(struct bug_entry *bug, struct pt_regs *regs)
+{
+	return BUG_TRAP_TYPE_BUG;
+}
+
 static inline void bug_get_file_line(struct bug_entry *bug, const char **file,
 				     unsigned int *line)
 {

lib/bug.c

@@ -183,18 +183,20 @@ static void __warn_printf(const char *fmt, struct pt_regs *regs)
 	printk("%s", fmt);
 }
 
-static enum bug_trap_type __report_bug(unsigned long bugaddr, struct pt_regs *regs)
+static enum bug_trap_type __report_bug(struct bug_entry *bug, unsigned long bugaddr, struct pt_regs *regs)
 {
 	bool warning, once, done, no_cut, has_args;
 	const char *file, *fmt;
 	unsigned line;
 
-	if (!is_valid_bugaddr(bugaddr))
-		return BUG_TRAP_TYPE_NONE;
+	if (!bug) {
+		if (!is_valid_bugaddr(bugaddr))
+			return BUG_TRAP_TYPE_NONE;
 
-	bug = find_bug(bugaddr);
-	if (!bug)
-		return BUG_TRAP_TYPE_NONE;
+		bug = find_bug(bugaddr);
+		if (!bug)
+			return BUG_TRAP_TYPE_NONE;
+	}
 
 	disable_trace_on_warning();
 
@@ -244,13 +246,25 @@ static enum bug_trap_type __report_bug(unsigned long bugaddr, struct pt_regs *re
 	return BUG_TRAP_TYPE_BUG;
 }
 
+enum bug_trap_type report_bug_entry(struct bug_entry *bug, struct pt_regs *regs)
+{
+	enum bug_trap_type ret;
+	bool rcu = false;
+
+	rcu = warn_rcu_enter();
+	ret = __report_bug(bug, 0, regs);
+	warn_rcu_exit(rcu);
+
+	return ret;
+}
+
 enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 {
 	enum bug_trap_type ret;
 	bool rcu = false;
 
 	rcu = warn_rcu_enter();
-	ret = __report_bug(bugaddr, regs);
+	ret = __report_bug(NULL, bugaddr, regs);
 	warn_rcu_exit(rcu);
 
 	return ret;