linux-kernel - [PATCH 04/11] bug: Add BUG_FORMAT

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Message-ID: <20250607095618.472060044@infradead.org>
Date: Sat, 07 Jun 2025 11:42:28 +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: [PATCH 04/11] bug: Add BUG_FORMAT_ARGS infrastructure

Add BUG_FORMAT_ARGS; when an architecture is able to provide a va_list
given pt_regs, use this to print format arguments.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 include/asm-generic/bug.h |    1 +
 lib/bug.c                 |   17 +++++++++++++++--
 2 files changed, 16 insertions(+), 2 deletions(-)

--- 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_ARGS		(1 << 4)
 #define BUGFLAG_TAINT(taint)	((taint) << 8)
 #define BUG_GET_TAINT(bug)	((bug)->flags >> 8)
 #endif
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -163,11 +163,23 @@ struct bug_entry *find_bug(unsigned long
 	return module_find_bug(bugaddr);
 }
 
-static void __warn_printf(const char *fmt)
+static void __warn_printf(const char *fmt, struct pt_regs *regs)
 {
 	if (!fmt)
 		return;
 
+#ifdef HAVE_ARCH_BUG_FORMAT_ARGS
+	if (regs) {
+		struct arch_va_list _args;
+		va_list *args = __warn_args(&_args, regs);
+
+		if (args) {
+			vprintk(fmt, *args);
+			return;
+		}
+	}
+#endif
+
 	printk("%s", fmt);
 }
 
@@ -193,6 +205,7 @@ static enum bug_trap_type __report_bug(u
 	once     = bug->flags & BUGFLAG_ONCE;
 	done     = bug->flags & BUGFLAG_DONE;
 	no_cut   = bug->flags & BUGFLAG_NO_CUT_HERE;
+	has_args = bug->flags & BUGFLAG_ARGS;
 
 	if (warning && once) {
 		if (done)
@@ -212,7 +225,7 @@ static enum bug_trap_type __report_bug(u
 	 */
 	if (!no_cut) {
 		printk(KERN_DEFAULT CUT_HERE);
-		__warn_printf(fmt);
+		__warn_printf(fmt, has_args ? regs : NULL);
 	}
 
 	if (warning) {