[RFC 2/8] bug: Add BUGFLAG_FORMAT infrastructure

Peter Zijlstra
2025-06-02T14:50:43Z

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@infradead.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,