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()
  ...

12 files changed, 317 insertions, 134 deletions

diff --git a/arch/arm64/include/asm/bug.h b/arch/arm64/include/asm/bug.h
index 28be048db3f6..bceeaec21fb9 100644
--- a/arch/arm64/include/asm/bug.h
+++ b/arch/arm64/include/asm/bug.h
@@ -19,7 +19,7 @@
 	unreachable();					\
 } while (0)
 
-#define __WARN_FLAGS(flags) __BUG_FLAGS(BUGFLAG_WARNING|(flags))
+#define __WARN_FLAGS(cond_str, flags) __BUG_FLAGS(BUGFLAG_WARNING|(flags))
 
 #define HAVE_ARCH_BUG
 
diff --git a/arch/loongarch/include/asm/bug.h b/arch/loongarch/include/asm/bug.h
index f6f254f2c5db..d090a5bec5eb 100644
--- a/arch/loongarch/include/asm/bug.h
+++ b/arch/loongarch/include/asm/bug.h
@@ -11,7 +11,7 @@
 #else
 #define __BUGVERBOSE_LOCATION(file, line)			\
 		.pushsection .rodata.str, "aMS", @progbits, 1;	\
-	10002:	.string file;					\
+	10002:	.ascii file "\0";				\
 		.popsection;					\
 								\
 		.long 10002b - .;				\
@@ -20,39 +20,38 @@
 #endif
 
 #ifndef CONFIG_GENERIC_BUG
-#define __BUG_ENTRY(flags)
+#define __BUG_ENTRY(cond_str, flags)
 #else
-#define __BUG_ENTRY(flags) 					\
+#define __BUG_ENTRY(cond_str, flags)				\
 		.pushsection __bug_table, "aw";			\
 		.align 2;					\
 	10000:	.long 10001f - .;				\
-		_BUGVERBOSE_LOCATION(__FILE__, __LINE__)	\
-		.short flags; 					\
+		_BUGVERBOSE_LOCATION(WARN_CONDITION_STR(cond_str) __FILE__, __LINE__) \
+		.short flags;					\
 		.popsection;					\
 	10001:
 #endif
 
-#define ASM_BUG_FLAGS(flags)					\
-	__BUG_ENTRY(flags)					\
+#define ASM_BUG_FLAGS(cond_str, flags)				\
+	__BUG_ENTRY(cond_str, flags)				\
 	break		BRK_BUG;
 
-#define ASM_BUG()	ASM_BUG_FLAGS(0)
+#define ASM_BUG()	ASM_BUG_FLAGS("", 0)
 
-#define __BUG_FLAGS(flags, extra)					\
-	asm_inline volatile (__stringify(ASM_BUG_FLAGS(flags))		\
-			     extra);
+#define __BUG_FLAGS(cond_str, flags, extra)			\
+	asm_inline volatile (__stringify(ASM_BUG_FLAGS(cond_str, flags)) extra);
 
-#define __WARN_FLAGS(flags)					\
+#define __WARN_FLAGS(cond_str, flags)				\
 do {								\
 	instrumentation_begin();				\
-	__BUG_FLAGS(BUGFLAG_WARNING|(flags), ANNOTATE_REACHABLE(10001b));\
+	__BUG_FLAGS(cond_str, BUGFLAG_WARNING|(flags), ANNOTATE_REACHABLE(10001b));\
 	instrumentation_end();					\
 } while (0)
 
 #define BUG()							\
 do {								\
 	instrumentation_begin();				\
-	__BUG_FLAGS(0, "");					\
+	__BUG_FLAGS("", 0, "");					\
 	unreachable();						\
 } while (0)
 
diff --git a/arch/parisc/include/asm/bug.h b/arch/parisc/include/asm/bug.h
index 833555f74ffa..5aa1623e4f2f 100644
--- a/arch/parisc/include/asm/bug.h
+++ b/arch/parisc/include/asm/bug.h
@@ -50,7 +50,7 @@
 #endif
 
 #ifdef CONFIG_DEBUG_BUGVERBOSE
-#define __WARN_FLAGS(flags)						\
+#define __WARN_FLAGS(cond_str, flags)					\
 	do {								\
 		asm volatile("\n"					\
 			     "1:\t" PARISC_BUG_BREAK_ASM "\n"		\
@@ -61,12 +61,12 @@
 			     "\t.short %1, %2\n"			\
 			     "\t.blockz %3-2*4-2*2\n"			\
 			     "\t.popsection"				\
-			     : : "i" (__FILE__), "i" (__LINE__),	\
+			     : : "i" (WARN_CONDITION_STR(cond_str) __FILE__), "i" (__LINE__), \
 			     "i" (BUGFLAG_WARNING|(flags)),		\
 			     "i" (sizeof(struct bug_entry)) );		\
 	} while(0)
 #else
-#define __WARN_FLAGS(flags)						\
+#define __WARN_FLAGS(cond_str, flags)					\
 	do {								\
 		asm volatile("\n"					\
 			     "1:\t" PARISC_BUG_BREAK_ASM "\n"		\
diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
index bbaa7e81f821..0db48977c70c 100644
--- a/arch/powerpc/include/asm/bug.h
+++ b/arch/powerpc/include/asm/bug.h
@@ -51,11 +51,11 @@
 	".previous\n"
 #endif
 
-#define BUG_ENTRY(insn, flags, ...)			\
+#define BUG_ENTRY(cond_str, insn, flags, ...)		\
 	__asm__ __volatile__(				\
 		"1:	" insn "\n"			\
 		_EMIT_BUG_ENTRY				\
-		: : "i" (__FILE__), "i" (__LINE__),	\
+		: : "i" (WARN_CONDITION_STR(cond_str) __FILE__), "i" (__LINE__),	\
 		  "i" (flags),				\
 		  "i" (sizeof(struct bug_entry)),	\
 		  ##__VA_ARGS__)
@@ -67,12 +67,12 @@
  */
 
 #define BUG() do {						\
-	BUG_ENTRY("twi 31, 0, 0", 0);				\
+	BUG_ENTRY("", "twi 31, 0, 0", 0);			\
 	unreachable();						\
 } while (0)
 #define HAVE_ARCH_BUG
 
-#define __WARN_FLAGS(flags) BUG_ENTRY("twi 31, 0, 0", BUGFLAG_WARNING | (flags))
+#define __WARN_FLAGS(cond_str, flags) BUG_ENTRY(cond_str, "twi 31, 0, 0", BUGFLAG_WARNING | (flags))
 
 #ifdef CONFIG_PPC64
 #define BUG_ON(x) do {						\
@@ -80,7 +80,7 @@
 		if (x)						\
 			BUG();					\
 	} else {						\
-		BUG_ENTRY(PPC_TLNEI " %4, 0", 0, "r" ((__force long)(x)));	\
+		BUG_ENTRY(#x, PPC_TLNEI " %4, 0", 0, "r" ((__force long)(x)));	\
 	}							\
 } while (0)
 
@@ -90,7 +90,7 @@
 		if (__ret_warn_on)				\
 			__WARN();				\
 	} else {						\
-		BUG_ENTRY(PPC_TLNEI " %4, 0",			\
+		BUG_ENTRY(#x, PPC_TLNEI " %4, 0",			\
 			  BUGFLAG_WARNING | BUGFLAG_TAINT(TAINT_WARN),	\
 			  "r" (__ret_warn_on));	\
 	}							\
diff --git a/arch/riscv/include/asm/bug.h b/arch/riscv/include/asm/bug.h
index 4c03e20ad11f..6f581b84d8fc 100644
--- a/arch/riscv/include/asm/bug.h
+++ b/arch/riscv/include/asm/bug.h
@@ -60,28 +60,28 @@ typedef u32 bug_insn_t;
 			".org 2b + " size "\n\t"                \
 			".popsection"				\
 
-#define __BUG_FLAGS(flags)					\
+#define __BUG_FLAGS(cond_str, flags)				\
 do {								\
 	__asm__ __volatile__ (					\
 		ARCH_WARN_ASM("%0", "%1", "%2", "%3")		\
 		:						\
-		: "i" (__FILE__), "i" (__LINE__),		\
+		: "i" (WARN_CONDITION_STR(cond_str) __FILE__), "i" (__LINE__),	\
 		  "i" (flags),					\
 		  "i" (sizeof(struct bug_entry)));              \
 } while (0)
 
 #else /* CONFIG_GENERIC_BUG */
-#define __BUG_FLAGS(flags) do {					\
+#define __BUG_FLAGS(cond_str, flags) do {			\
 	__asm__ __volatile__ ("ebreak\n");			\
 } while (0)
 #endif /* CONFIG_GENERIC_BUG */
 
 #define BUG() do {						\
-	__BUG_FLAGS(0);						\
+	__BUG_FLAGS("", 0);					\
 	unreachable();						\
 } while (0)
 
-#define __WARN_FLAGS(flags) __BUG_FLAGS(BUGFLAG_WARNING|(flags))
+#define __WARN_FLAGS(cond_str, flags) __BUG_FLAGS(cond_str, BUGFLAG_WARNING|(flags))
 
 #define ARCH_WARN_REACHABLE
 
diff --git a/arch/s390/include/asm/bug.h b/arch/s390/include/asm/bug.h
index c500d45fb465..acb4b13d98c5 100644
--- a/arch/s390/include/asm/bug.h
+++ b/arch/s390/include/asm/bug.h
@@ -2,69 +2,55 @@
 #ifndef _ASM_S390_BUG_H
 #define _ASM_S390_BUG_H
 
-#include <linux/compiler.h>
-
-#ifdef CONFIG_BUG
-
-#ifdef CONFIG_DEBUG_BUGVERBOSE
-
-#define __EMIT_BUG(x) do {					\
-	asm_inline volatile(					\
-		"0:	mc	0,0\n"				\
-		".section .rodata.str,\"aMS\",@progbits,1\n"	\
-		"1:	.asciz	\""__FILE__"\"\n"		\
-		".previous\n"					\
-		".section __bug_table,\"aw\"\n"			\
-		"2:	.long	0b-.\n"				\
-		"	.long	1b-.\n"				\
-		"	.short	%0,%1\n"			\
-		"	.org	2b+%2\n"			\
-		".previous\n"					\
-		: : "i" (__LINE__),				\
-		    "i" (x),					\
-		    "i" (sizeof(struct bug_entry)));		\
-} while (0)
-
-#else /* CONFIG_DEBUG_BUGVERBOSE */
-
-#define __EMIT_BUG(x) do {					\
-	asm_inline volatile(					\
-		"0:	mc	0,0\n"				\
-		".section __bug_table,\"aw\"\n"			\
-		"1:	.long	0b-.\n"				\
-		"	.short	%0\n"				\
-		"	.org	1b+%1\n"			\
-		".previous\n"					\
-		: : "i" (x),					\
-		    "i" (sizeof(struct bug_entry)));		\
+#include <linux/stringify.h>
+
+#ifndef CONFIG_DEBUG_BUGVERBOSE
+#define _BUGVERBOSE_LOCATION(file, line)
+#else
+#define __BUGVERBOSE_LOCATION(file, line)			\
+		.pushsection .rodata.str, "aMS", @progbits, 1;	\
+	10002:	.ascii file "\0";				\
+		.popsection;					\
+								\
+		.long 10002b - .;				\
+		.short line;
+#define _BUGVERBOSE_LOCATION(file, line) __BUGVERBOSE_LOCATION(file, line)
+#endif
+
+#ifndef CONFIG_GENERIC_BUG
+#define __BUG_ENTRY(cond_str, flags)
+#else
+#define __BUG_ENTRY(cond_str, flags)				\
+		.pushsection __bug_table, "aw";			\
+		.align 4;					\
+	10000:	.long 10001f - .;				\
+		_BUGVERBOSE_LOCATION(WARN_CONDITION_STR(cond_str) __FILE__, __LINE__) \
+		.short flags;					\
+		.popsection;					\
+	10001:
+#endif
+
+#define ASM_BUG_FLAGS(cond_str, flags)				\
+	__BUG_ENTRY(cond_str, flags)				\
+	mc		0,0
+
+#define ASM_BUG()	ASM_BUG_FLAGS("", 0)
+
+#define __BUG_FLAGS(cond_str, flags)				\
+	asm_inline volatile(__stringify(ASM_BUG_FLAGS(cond_str, flags)));
+
+#define __WARN_FLAGS(cond_str, flags)				\
+do {								\
+	__BUG_FLAGS(cond_str, BUGFLAG_WARNING|(flags));		\
 } while (0)
 
-#endif /* CONFIG_DEBUG_BUGVERBOSE */
-
-#define BUG() do {					\
-	__EMIT_BUG(0);					\
-	unreachable();					\
+#define BUG()							\
+do {								\
+	__BUG_FLAGS("", 0);					\
+	unreachable();						\
 } while (0)
 
-#define __WARN_FLAGS(flags) do {			\
-	__EMIT_BUG(BUGFLAG_WARNING|(flags));		\
-} while (0)
-
-#define WARN_ON(x) ({					\
-	int __ret_warn_on = !!(x);			\
-	if (__builtin_constant_p(__ret_warn_on)) {	\
-		if (__ret_warn_on)			\
-			__WARN();			\
-	} else {					\
-		if (unlikely(__ret_warn_on))		\
-			__WARN();			\
-	}						\
-	unlikely(__ret_warn_on);			\
-})
-
 #define HAVE_ARCH_BUG
-#define HAVE_ARCH_WARN_ON
-#endif /* CONFIG_BUG */
 
 #include <asm-generic/bug.h>
 
diff --git a/arch/sh/include/asm/bug.h b/arch/sh/include/asm/bug.h
index 05a485c4fabc..891276687355 100644
--- a/arch/sh/include/asm/bug.h
+++ b/arch/sh/include/asm/bug.h
@@ -52,14 +52,14 @@ do {							\
 	unreachable();					\
 } while (0)
 
-#define __WARN_FLAGS(flags)				\
+#define __WARN_FLAGS(cond_str, flags)			\
 do {							\
 	__asm__ __volatile__ (				\
 		"1:\t.short %O0\n"			\
 		 _EMIT_BUG_ENTRY			\
 		 :					\
 		 : "n" (TRAPA_BUG_OPCODE),		\
-		   "i" (__FILE__),			\
+		   "i" (WARN_CONDITION_STR(cond_str) __FILE__),	\
 		   "i" (__LINE__),			\
 		   "i" (BUGFLAG_WARNING|(flags)),	\
 		   "i" (sizeof(struct bug_entry)));	\
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index c4c21e8d0772..34fb46d5341b 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -381,7 +381,7 @@ config GENERIC_CSUM
 config GENERIC_BUG
 	def_bool y
 	depends on BUG
-	select GENERIC_BUG_RELATIVE_POINTERS if X86_64
+	select GENERIC_BUG_RELATIVE_POINTERS
 
 config GENERIC_BUG_RELATIVE_POINTERS
 	bool
diff --git a/arch/x86/entry/entry.S b/arch/x86/entry/entry.S
index 8e9a0cc20a4a..772c64ed4523 100644
--- a/arch/x86/entry/entry.S
+++ b/arch/x86/entry/entry.S
@@ -32,6 +32,14 @@ SYM_FUNC_END(write_ibpb)
 /* For KVM */
 EXPORT_SYMBOL_GPL(write_ibpb);
 
+SYM_FUNC_START(__WARN_trap)
+	ANNOTATE_NOENDBR
+	ANNOTATE_REACHABLE
+	ud1 (%edx), %_ASM_ARG1
+	RET
+SYM_FUNC_END(__WARN_trap)
+EXPORT_SYMBOL(__WARN_trap)
+
 .popsection
 
 /*
diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index 372f4018880c..ab5bba6cf7f5 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -7,6 +7,11 @@
 #include <linux/objtool.h>
 #include <asm/asm.h>
 
+#ifndef __ASSEMBLY__
+struct bug_entry;
+extern void __WARN_trap(struct bug_entry *bug, ...);
+#endif
+
 /*
  * Despite that some emulators terminate on UD2, we use it for WARN().
  */
@@ -31,53 +36,77 @@
 #define BUG_UD2			0xfffe
 #define BUG_UD1			0xfffd
 #define BUG_UD1_UBSAN		0xfffc
+#define BUG_UD1_WARN		0xfffb
 #define BUG_UDB			0xffd6
 #define BUG_LOCK		0xfff0
 
 #ifdef CONFIG_GENERIC_BUG
 
-#ifdef CONFIG_X86_32
-# define __BUG_REL(val)	".long " val
+#ifdef CONFIG_DEBUG_BUGVERBOSE
+#define __BUG_ENTRY_VERBOSE(file, line)					\
+	"\t.long " file " - .\t# bug_entry::file\n"			\
+	"\t.word " line     "\t# bug_entry::line\n"
 #else
-# define __BUG_REL(val)	".long " val " - ."
+#define __BUG_ENTRY_VERBOSE(file, line)
 #endif
 
-#ifdef CONFIG_DEBUG_BUGVERBOSE
-#define __BUG_ENTRY(file, line, flags)					\
-	"2:\t" __BUG_REL("1b") "\t# bug_entry::bug_addr\n"		\
-	"\t" __BUG_REL(file)   "\t# bug_entry::file\n"			\
-	"\t.word " line        "\t# bug_entry::line\n"			\
-	"\t.word " flags       "\t# bug_entry::flags\n"
+#if defined(CONFIG_X86_64) || defined(CONFIG_DEBUG_BUGVERBOSE_DETAILED)
+#define HAVE_ARCH_BUG_FORMAT
+#define __BUG_ENTRY_FORMAT(format)					\
+	"\t.long " format " - .\t# bug_entry::format\n"
 #else
-#define __BUG_ENTRY(file, line, flags)					\
-	"2:\t" __BUG_REL("1b") "\t# bug_entry::bug_addr\n"		\
-	"\t.word " flags       "\t# bug_entry::flags\n"
+#define __BUG_ENTRY_FORMAT(format)
+#endif
+
+#ifdef CONFIG_X86_64
+#define HAVE_ARCH_BUG_FORMAT_ARGS
 #endif
 
-#define _BUG_FLAGS_ASM(ins, file, line, flags, size, extra)		\
-	"1:\t" ins "\n"							\
-	".pushsection __bug_table,\"aw\"\n"				\
+#define __BUG_ENTRY(format, file, line, flags)				\
+	"\t.long 1b - ."	"\t# bug_entry::bug_addr\n"		\
+	__BUG_ENTRY_FORMAT(format)					\
+	__BUG_ENTRY_VERBOSE(file, line)					\
+	"\t.word " flags	"\t# bug_entry::flags\n"
+
+#define _BUG_FLAGS_ASM(format, file, line, flags, size, extra)		\
+	".pushsection __bug_table,\"aw\"\n\t"				\
 	ANNOTATE_DATA_SPECIAL						\
-	__BUG_ENTRY(file, line, flags)					\
+	"2:\n\t"							\
+	__BUG_ENTRY(format, file, line, flags)				\
 	"\t.org 2b + " size "\n"					\
 	".popsection\n"							\
 	extra
 
-#define _BUG_FLAGS(ins, flags, extra)					\
+#ifdef CONFIG_DEBUG_BUGVERBOSE_DETAILED
+#define WARN_CONDITION_STR(cond_str) cond_str
+#else
+#define WARN_CONDITION_STR(cond_str) ""
+#endif
+
+#define _BUG_FLAGS(cond_str, ins, flags, extra)				\
 do {									\
-	asm_inline volatile(_BUG_FLAGS_ASM(ins, "%c0",			\
-					   "%c1", "%c2", "%c3", extra)	\
-		     : : "i" (__FILE__), "i" (__LINE__),		\
-			 "i" (flags),					\
-			 "i" (sizeof(struct bug_entry)));		\
+	asm_inline volatile("1:\t" ins "\n"				\
+			    _BUG_FLAGS_ASM("%c[fmt]", "%c[file]",	\
+					   "%c[line]", "%c[fl]",	\
+					   "%c[size]", extra)		\
+		   : : [fmt] "i" (WARN_CONDITION_STR(cond_str)),	\
+		       [file] "i" (__FILE__),				\
+		       [line] "i" (__LINE__),				\
+		       [fl] "i" (flags),				\
+		       [size] "i" (sizeof(struct bug_entry)));		\
 } while (0)
 
 #define ARCH_WARN_ASM(file, line, flags, size)				\
-	_BUG_FLAGS_ASM(ASM_UD2, file, line, flags, size, "")
+	".pushsection .rodata.str1.1, \"aMS\", @progbits, 1\n"		\
+	"99:\n"								\
+	"\t.string \"\"\n"						\
+	".popsection\n"							\
+	"1:\t " ASM_UD2 "\n"						\
+	_BUG_FLAGS_ASM("99b", file, line, flags, size, "")
 
 #else
 
-#define _BUG_FLAGS(ins, flags, extra)  asm volatile(ins)
+#define _BUG_FLAGS(cond_str, ins, flags, extra)  asm volatile(ins)
 
 #endif /* CONFIG_GENERIC_BUG */
 
@@ -85,7 +114,7 @@ do {									\
 #define BUG()							\
 do {								\
 	instrumentation_begin();				\
-	_BUG_FLAGS(ASM_UD2, 0, "");				\
+	_BUG_FLAGS("", ASM_UD2, 0, "");				\
 	__builtin_unreachable();				\
 } while (0)
 
@@ -98,14 +127,69 @@ do {								\
 
 #define ARCH_WARN_REACHABLE	ANNOTATE_REACHABLE(1b)
 
-#define __WARN_FLAGS(flags)					\
-do {								\
-	__auto_type __flags = BUGFLAG_WARNING|(flags);		\
-	instrumentation_begin();				\
-	_BUG_FLAGS(ASM_UD2, __flags, ARCH_WARN_REACHABLE);	\
-	instrumentation_end();					\
+#define __WARN_FLAGS(cond_str, flags)					\
+do {									\
+	__auto_type __flags = BUGFLAG_WARNING|(flags);			\
+	instrumentation_begin();					\
+	_BUG_FLAGS(cond_str, ASM_UD2, __flags, ARCH_WARN_REACHABLE);	\
+	instrumentation_end();						\
+} while (0)
+
+#ifdef HAVE_ARCH_BUG_FORMAT_ARGS
+
+#ifndef __ASSEMBLY__
+#include <linux/static_call_types.h>
+DECLARE_STATIC_CALL(WARN_trap, __WARN_trap);
+
+struct pt_regs;
+struct sysv_va_list { /* from AMD64 System V ABI */
+	unsigned int gp_offset;
+	unsigned int fp_offset;
+	void *overflow_arg_area;
+	void *reg_save_area;
+};
+struct arch_va_list {
+	unsigned long regs[6];
+	struct sysv_va_list args;
+};
+extern void *__warn_args(struct arch_va_list *args, struct pt_regs *regs);
+#endif /* __ASSEMBLY__ */
+
+#define __WARN_bug_entry(flags, format) ({				\
+	struct bug_entry *bug;						\
+	asm_inline volatile("lea (2f)(%%rip), %[addr]\n1:\n"		\
+			    _BUG_FLAGS_ASM("%c[fmt]", "%c[file]",	\
+					   "%c[line]", "%c[fl]",	\
+					   "%c[size]", "")		\
+		   : [addr] "=r" (bug)					\
+		   : [fmt] "i" (format),				\
+		     [file] "i" (__FILE__),				\
+		     [line] "i" (__LINE__),				\
+		     [fl] "i" (flags),					\
+		     [size] "i" (sizeof(struct bug_entry)));		\
+	bug; })
+
+#define __WARN_print_arg(flags, format, arg...)				\
+do {									\
+	int __flags = (flags) | BUGFLAG_WARNING | BUGFLAG_ARGS ;	\
+	static_call_mod(WARN_trap)(__WARN_bug_entry(__flags, format), ## arg); \
+	asm (""); /* inhibit tail-call optimization */			\
 } while (0)
 
+#define __WARN_printf(taint, fmt, arg...) \
+	__WARN_print_arg(BUGFLAG_TAINT(taint), fmt, ## arg)
+
+#define WARN_ONCE(cond, format, arg...) ({				\
+	int __ret_warn_on = !!(cond);					\
+	if (unlikely(__ret_warn_on)) {					\
+		__WARN_print_arg(BUGFLAG_ONCE|BUGFLAG_TAINT(TAINT_WARN),\
+				format, ## arg);			\
+	}								\
+	__ret_warn_on;							\
+})
+
+#endif /* HAVE_ARCH_BUG_FORMAT_ARGS */
+
 #include <asm-generic/bug.h>
 
 #endif /* _ASM_X86_BUG_H */
diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c
index 378c388d1b31..2892cdb14563 100644
--- a/arch/x86/kernel/static_call.c
+++ b/arch/x86/kernel/static_call.c
@@ -26,6 +26,11 @@ static const u8 xor5rax[] = { 0x2e, 0x2e, 0x2e, 0x31, 0xc0 };
 
 static const u8 retinsn[] = { RET_INSN_OPCODE, 0xcc, 0xcc, 0xcc, 0xcc };
 
+/*
+ * ud1    (%edx),%rdi -- see __WARN_trap() / decode_bug()
+ */
+static const u8 warninsn[] = { 0x67, 0x48, 0x0f, 0xb9, 0x3a };
+
 static u8 __is_Jcc(u8 *insn) /* Jcc.d32 */
 {
 	u8 ret = 0;
@@ -69,7 +74,10 @@ static void __ref __static_call_transform(void *insn, enum insn_type type,
 			emulate = code;
 			code = &xor5rax;
 		}
-
+		if (func == &__WARN_trap) {
+			emulate = code;
+			code = &warninsn;
+		}
 		break;
 
 	case NOP:
@@ -128,7 +136,8 @@ static void __static_call_validate(u8 *insn, bool tail, bool tramp)
 	} else {
 		if (opcode == CALL_INSN_OPCODE ||
 		    !memcmp(insn, x86_nops[5], 5) ||
-		    !memcmp(insn, xor5rax, 5))
+		    !memcmp(insn, xor5rax, 5) ||
+		    !memcmp(insn, warninsn, 5))
 			return;
 	}
 
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 6b22611e69cc..cb324cc1fd99 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -31,6 +31,7 @@
 #include <linux/kexec.h>
 #include <linux/sched.h>
 #include <linux/sched/task_stack.h>
+#include <linux/static_call.h>
 #include <linux/timer.h>
 #include <linux/init.h>
 #include <linux/bug.h>
@@ -102,25 +103,37 @@ __always_inline int is_valid_bugaddr(unsigned long addr)
  * UBSan{0}:     67 0f b9 00             ud1    (%eax),%eax
  * UBSan{10}:    67 0f b9 40 10          ud1    0x10(%eax),%eax
  * static_call:  0f b9 cc                ud1    %esp,%ecx
+ * __WARN_trap:  67 48 0f b9 3a          ud1    (%edx),%reg
  *
- * Notably UBSAN uses EAX, static_call uses ECX.
+ * Notable, since __WARN_trap can use all registers, the distinction between
+ * UD1 users is through R/M.
  */
 __always_inline int decode_bug(unsigned long addr, s32 *imm, int *len)
 {
 	unsigned long start = addr;
+	u8 v, reg, rm, rex = 0;
+	int type = BUG_UD1;
 	bool lock = false;
-	u8 v;
 
 	if (addr < TASK_SIZE_MAX)
 		return BUG_NONE;
 
-	v = *(u8 *)(addr++);
-	if (v == INSN_ASOP)
+	for (;;) {
 		v = *(u8 *)(addr++);
+		if (v == INSN_ASOP)
+			continue;
 
-	if (v == INSN_LOCK) {
-		lock = true;
-		v = *(u8 *)(addr++);
+		if (v == INSN_LOCK) {
+			lock = true;
+			continue;
+		}
+
+		if ((v & 0xf0) == 0x40) {
+			rex = v;
+			continue;
+		}
+
+		break;
 	}
 
 	switch (v) {
@@ -156,18 +169,33 @@ __always_inline int decode_bug(unsigned long addr, s32 *imm, int *len)
 	if (X86_MODRM_MOD(v) != 3 && X86_MODRM_RM(v) == 4)
 		addr++;			/* SIB */
 
+	reg = X86_MODRM_REG(v) + 8*!!X86_REX_R(rex);
+	rm  = X86_MODRM_RM(v)  + 8*!!X86_REX_B(rex);
+
 	/* Decode immediate, if present */
 	switch (X86_MODRM_MOD(v)) {
 	case 0: if (X86_MODRM_RM(v) == 5)
-			addr += 4; /* RIP + disp32 */
+			addr += 4;	/* RIP + disp32 */
+
+		if (rm == 0)		/* (%eax) */
+			type = BUG_UD1_UBSAN;
+
+		if (rm == 2) {		/* (%edx) */
+			*imm = reg;
+			type = BUG_UD1_WARN;
+		}
 		break;
 
 	case 1: *imm = *(s8 *)addr;
 		addr += 1;
+		if (rm == 0)		/* (%eax) */
+			type = BUG_UD1_UBSAN;
 		break;
 
 	case 2: *imm = *(s32 *)addr;
 		addr += 4;
+		if (rm == 0)		/* (%eax) */
+			type = BUG_UD1_UBSAN;
 		break;
 
 	case 3: break;
@@ -176,12 +204,76 @@ __always_inline int decode_bug(unsigned long addr, s32 *imm, int *len)
 	/* record instruction length */
 	*len = addr - start;
 
-	if (X86_MODRM_REG(v) == 0)	/* EAX */
-		return BUG_UD1_UBSAN;
+	return type;
+}
 
-	return BUG_UD1;
+static inline unsigned long pt_regs_val(struct pt_regs *regs, int nr)
+{
+	int offset = pt_regs_offset(regs, nr);
+	if (WARN_ON_ONCE(offset < -0))
+		return 0;
+	return *((unsigned long *)((void *)regs + offset));
 }
 
+#ifdef HAVE_ARCH_BUG_FORMAT_ARGS
+DEFINE_STATIC_CALL(WARN_trap, __WARN_trap);
+EXPORT_STATIC_CALL_TRAMP(WARN_trap);
+
+/*
+ * Create a va_list from an exception context.
+ */
+void *__warn_args(struct arch_va_list *args, struct pt_regs *regs)
+{
+	/*
+	 * Register save area; populate with function call argument registers
+	 */
+	args->regs[0] = regs->di;
+	args->regs[1] = regs->si;
+	args->regs[2] = regs->dx;
+	args->regs[3] = regs->cx;
+	args->regs[4] = regs->r8;
+	args->regs[5] = regs->r9;
+
+	/*
+	 * From the ABI document:
+	 *
+	 * @gp_offset - the element holds the offset in bytes from
+	 * reg_save_area to the place where the next available general purpose
+	 * argument register is saved. In case all argument registers have
+	 * been exhausted, it is set to the value 48 (6*8).
+	 *
+	 * @fp_offset - the element holds the offset in bytes from
+	 * reg_save_area to the place where the next available floating point
+	 * argument is saved. In case all argument registers have been
+	 * exhausted, it is set to the value 176 (6*8 + 8*16)
+	 *
+	 * @overflow_arg_area - this pointer is used to fetch arguments passed
+	 * on the stack. It is initialized with the address of the first
+	 * argument passed on the stack, if any, and then always updated to
+	 * point to the start of the next argument on the stack.
+	 *
+	 * @reg_save_area - the element points to the start of the register
+	 * save area.
+	 *
+	 * Notably the vararg starts with the second argument and there are no
+	 * floating point arguments in the kernel.
+	 */
+	args->args.gp_offset = 1*8;
+	args->args.fp_offset = 6*8 + 8*16;
+	args->args.reg_save_area = &args->regs;
+	args->args.overflow_arg_area = (void *)regs->sp;
+
+	/*
+	 * If the exception came from __WARN_trap, there is a return
+	 * address on the stack, skip that. This is why any __WARN_trap()
+	 * caller must inhibit tail-call optimization.
+	 */
+	if ((void *)regs->ip == &__WARN_trap)
+		args->args.overflow_arg_area += 8;
+
+	return &args->args;
+}
+#endif /* HAVE_ARCH_BUG_FORMAT */
 
 static nokprobe_inline int
 do_trap_no_signal(struct task_struct *tsk, int trapnr, const char *str,
@@ -334,6 +426,11 @@ static noinstr bool handle_bug(struct pt_regs *regs)
 		raw_local_irq_enable();
 
 	switch (ud_type) {
+	case BUG_UD1_WARN:
+		if (report_bug_entry((void *)pt_regs_val(regs, ud_imm), regs) == BUG_TRAP_TYPE_WARN)
+			handled = true;
+		break;
+
 	case BUG_UD2:
 		if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN) {
 			handled = true;