Merge tag 'core-bugs-2025-12-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull bug handling infrastructure updates from Ingo Molnar:
 "Core updates:

   - Improve WARN(), which has vararg printf like arguments, to work
     with the x86 #UD based WARN-optimizing infrastructure by hiding the
     format in the bug_table and replacing this first argument with the
     address of the bug-table entry, while making the actual function
     that's called a UD1 instruction (Peter Zijlstra)

   - Introduce the CONFIG_DEBUG_BUGVERBOSE_DETAILED Kconfig switch (Ingo
     Molnar, s390 support by Heiko Carstens)

  Fixes and cleanups:

   - bugs/s390: Remove private WARN_ON() implementation (Heiko Carstens)

   - <asm/bugs.h>: Make i386 use GENERIC_BUG_RELATIVE_POINTERS (Peter
     Zijlstra)"

* tag 'core-bugs-2025-12-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (31 commits)
  x86/bugs: Make i386 use GENERIC_BUG_RELATIVE_POINTERS
  x86/bug: Fix BUG_FORMAT vs KASLR
  x86_64/bug: Inline the UD1
  x86/bug: Implement WARN_ONCE()
  x86_64/bug: Implement __WARN_printf()
  x86/bug: Use BUG_FORMAT for DEBUG_BUGVERBOSE_DETAILED
  x86/bug: Add BUG_FORMAT basics
  bug: Allow architectures to provide __WARN_printf()
  bug: Implement WARN_ON() using __WARN_FLAGS()
  bug: Add report_bug_entry()
  bug: Add BUG_FORMAT_ARGS infrastructure
  bug: Clean up CONFIG_GENERIC_BUG_RELATIVE_POINTERS
  bug: Add BUG_FORMAT infrastructure
  x86: Rework __bug_table helpers
  bugs/s390: Remove private WARN_ON() implementation
  bugs/core: Reorganize fields in the first line of WARNING output, add ->comm[] output
  bugs/sh: Concatenate 'cond_str' with '__FILE__' in __WARN_FLAGS(), to extend WARN_ON/BUG_ON output
  bugs/parisc: Concatenate 'cond_str' with '__FILE__' in __WARN_FLAGS(), to extend WARN_ON/BUG_ON output
  bugs/riscv: Concatenate 'cond_str' with '__FILE__' in __BUG_FLAGS(), to extend WARN_ON/BUG_ON output
  bugs/riscv: Pass in 'cond_str' to __BUG_FLAGS()
  ...

lib/Kconfig.debug

@@ -206,6 +206,16 @@ config DEBUG_BUGVERBOSE
 	  of the BUG call as well as the EIP and oops trace.  This aids
 	  debugging but costs about 70-100K of memory.
 
+config DEBUG_BUGVERBOSE_DETAILED
+	bool "Verbose WARN_ON_ONCE() reporting (adds 100K)" if DEBUG_BUGVERBOSE
+	help
+	  Say Y here to make WARN_ON_ONCE() output the condition string of the
+	  warning, in addition to the file name and line number.
+	  This helps debugging, but costs about 100K of memory.
+
+	  Say N if unsure.
+
+
 endmenu # "printk and dmesg options"
 
 config DEBUG_KERNEL

lib/bug.c

@@ -139,6 +139,29 @@ void bug_get_file_line(struct bug_entry *bug, const char **file,
 #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
+	/*
+	 * Allow an architecture to:
+	 *  - relative encode NULL (difficult vs KASLR);
+	 *  - use a literal 0 (there are no valid objects inside
+	 *    the __bug_table itself to refer to after all);
+	 *  - use an empty string.
+	 */
+	if (bug->format_disp)
+		format = (const char *)&bug->format_disp + bug->format_disp;
+	if (format && format[0] == '\0')
+		format = NULL;
+#else
+	format = bug->format;
+#endif
+#endif
+	return format;
+}
+
 struct bug_entry *find_bug(unsigned long bugaddr)
 {
 	struct bug_entry *bug;
@@ -150,26 +173,51 @@ struct bug_entry *find_bug(unsigned long bugaddr)
 	return module_find_bug(bugaddr);
 }
 
-static enum bug_trap_type __report_bug(unsigned long bugaddr, struct pt_regs *regs)
+static void __warn_printf(const char *fmt, struct pt_regs *regs)
 {
-	struct bug_entry *bug;
-	const char *file;
-	unsigned line, warning, once, done;
+	if (!fmt)
+		return;
 
-	if (!is_valid_bugaddr(bugaddr))
-		return BUG_TRAP_TYPE_NONE;
+#ifdef HAVE_ARCH_BUG_FORMAT_ARGS
+	if (regs) {
+		struct arch_va_list _args;
+		va_list *args = __warn_args(&_args, regs);
 
-	bug = find_bug(bugaddr);
-	if (!bug)
-		return BUG_TRAP_TYPE_NONE;
+		if (args) {
+			vprintk(fmt, *args);
+			return;
+		}
+	}
+#endif
+
+	printk("%s", fmt);
+}
+
+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 (!bug) {
+		if (!is_valid_bugaddr(bugaddr))
+			return BUG_TRAP_TYPE_NONE;
+
+		bug = find_bug(bugaddr);
+		if (!bug)
+			return BUG_TRAP_TYPE_NONE;
+	}
 
 	disable_trace_on_warning();
 
 	bug_get_file_line(bug, &file, &line);
+	fmt = bug_get_format(bug);
 
-	warning = (bug->flags & BUGFLAG_WARNING) != 0;
-	once = (bug->flags & BUGFLAG_ONCE) != 0;
-	done = (bug->flags & BUGFLAG_DONE) != 0;
+	warning  = bug->flags & BUGFLAG_WARNING;
+	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)
@@ -187,8 +235,10 @@ static enum bug_trap_type __report_bug(unsigned long bugaddr, struct pt_regs *re
 	 * "cut here" line now. WARN() issues its own "cut here" before the
 	 * extra debugging message it writes before triggering the handler.
 	 */
-	if ((bug->flags & BUGFLAG_NO_CUT_HERE) == 0)
+	if (!no_cut) {
 		printk(KERN_DEFAULT CUT_HERE);
+		__warn_printf(fmt, has_args ? regs : NULL);
+	}
 
 	if (warning) {
 		/* this is a WARN_ON rather than BUG/BUG_ON */
@@ -206,13 +256,25 @@ 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;