linux-kernel - [RFC 2/8] bug: Add BUGFLAG

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Message-ID: <20250602144755.436183368@infradead.org>
Date: Mon, 02 Jun 2025 16:42:03 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
 peterz@...radead.org,
 kees@...nel.org,
 acarmina@...hat.com,
 jpoimboe@...nel.org,
 mark.rutland@....com,
 torvalds@...uxfoundation.org
Subject: [RFC 2/8] bug: Add BUGFLAG_FORMAT infrastructure

Add BUGFLAG_FORMAT; an architecture opt-in feature that allows adding
the WARN_printf() format string to the bug_entry table.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 include/asm-generic/bug.h |    8 ++++++++
 lib/bug.c                 |   20 ++++++++++++++++++++
 2 files changed, 28 insertions(+)

--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -13,6 +13,7 @@
 #define BUGFLAG_ONCE		(1 << 1)
 #define BUGFLAG_DONE		(1 << 2)
 #define BUGFLAG_NO_CUT_HERE	(1 << 3)	/* CUT_HERE already sent */
+#define BUGFLAG_FORMAT		(1 << 4)
 #define BUGFLAG_TAINT(taint)	((taint) << 8)
 #define BUG_GET_TAINT(bug)	((bug)->flags >> 8)
 #endif
@@ -36,6 +37,13 @@ struct bug_entry {
 #else
 	signed int	bug_addr_disp;
 #endif
+#ifdef HAVE_ARCH_BUG_FORMAT
+#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
+	const char	*format;
+#else
+	signed int	format_disp;
+#endif
+#endif
 #ifdef CONFIG_DEBUG_BUGVERBOSE
 #ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
 	const char	*file;
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -139,6 +139,19 @@ void bug_get_file_line(struct bug_entry
 #endif
 }
 
+static const char *bug_get_format(struct bug_entry *bug)
+{
+	const char *format = NULL;
+#ifdef HAVE_ARCH_BUG_FORMAT
+#ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
+	format = (const char *)&bug->format_disp + bug->format_disp;
+#else
+	format = bug->format;
+#endif
+#endif
+	return format;
+}
+
 struct bug_entry *find_bug(unsigned long bugaddr)
 {
 	struct bug_entry *bug;
@@ -150,6 +163,10 @@ struct bug_entry *find_bug(unsigned long
 	return module_find_bug(bugaddr);
 }
 
+#ifndef __warn_printf
+#define __warn_printf(...)
+#endif
+
 static enum bug_trap_type __report_bug(unsigned long bugaddr, struct pt_regs *regs)
 {
 	struct bug_entry *bug;
@@ -190,6 +207,9 @@ static enum bug_trap_type __report_bug(u
 	if ((bug->flags & BUGFLAG_NO_CUT_HERE) == 0)
 		printk(KERN_DEFAULT CUT_HERE);
 
+	if (bug->flags & BUGFLAG_FORMAT)
+		__warn_printf(bug_get_format(bug), regs);
+
 	if (warning) {
 		/* this is a WARN_ON rather than BUG/BUG_ON */
 		__warn(file, line, (void *)bugaddr, BUG_GET_TAINT(bug), regs,