linux-kernel - [PATCH 2/9] s390/bug: Convert to inline assembly with input operands

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Message-ID: <20251209121701.1856271-3-hca@linux.ibm.com>
Date: Tue,  9 Dec 2025 13:16:54 +0100
From: Heiko Carstens <hca@...ux.ibm.com>
To: Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mark Rutland <mark.rutland@....com>, Arnd Bergmann <arnd@...db.de>,
        Jens Remus <jremus@...ux.ibm.com>,
        Stefan Schulze Frielinghaus <stefansf@...ux.ibm.com>,
        Juergen Christ <jchrist@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org
Subject: [PATCH 2/9] s390/bug: Convert to inline assembly with input operands

Rewrite the bug inline assembly so it uses input operands again instead of
pure macro replacements. This more or less reverts the conversion done when
'cond_str' support was added [1].

Reason for this is that the upcoming __WARN_printf() implementation
requires an inline assembly with an output operand. At the same time input
strings (format specifier and condition string) may contain the special '%'
character. As soon as an inline assembly is specified to have input/output
operands the '%' has a special meaning: e.g. converting the existing

 #define __BUG_FLAGS(cond_str, flags) \
   asm_inline volatile(__stringify(ASM_BUG_FLAGS(cond_str, flags)));

to

 #define __BUG_FLAGS(cond_str, flags) \
   asm_inline volatile(__stringify(ASM_BUG_FLAGS(cond_str, flags))::);

will result in a compile error as soon as 'cond_str' contains a '%'
character:

net/core/neighbour.c: In function ‘neigh_table_init’:
././include/linux/compiler_types.h:546:20: error: invalid 'asm': invalid %-code
...
net/core/neighbour.c:1838:17: note: in expansion of macro ‘WARN_ON’
 1838 |                 WARN_ON(tbl->entry_size % NEIGH_PRIV_ALIGN);
      |                 ^~~~~~~

Convert the code, use immediate operands, and also add comments similar to
x86 which are emitted to the generated assembly file, which makes debugging
much easier.

[1] 6584ff203aec ("bugs/s390: Use 'cond_str' in __EMIT_BUG()")

Signed-off-by: Heiko Carstens <hca@...ux.ibm.com>
---
 arch/s390/include/asm/bug.h | 71 ++++++++++++++++---------------------
 1 file changed, 30 insertions(+), 41 deletions(-)

diff --git a/arch/s390/include/asm/bug.h b/arch/s390/include/asm/bug.h
index ee9221bb5d18..61496143a382 100644
--- a/arch/s390/include/asm/bug.h
+++ b/arch/s390/include/asm/bug.h
@@ -2,55 +2,44 @@
 #ifndef _ASM_S390_BUG_H
 #define _ASM_S390_BUG_H
 
-#include <linux/stringify.h>
+#include <linux/compiler.h>
 
 #ifdef CONFIG_BUG
 
-#ifndef CONFIG_DEBUG_BUGVERBOSE
-#define _BUGVERBOSE_LOCATION(file, line)
+#ifdef CONFIG_DEBUG_BUGVERBOSE
+#define __BUG_ENTRY_VERBOSE(file, line)					\
+	"	.long	" file " - .	# bug_entry::file\n"		\
+	"	.short	" line "	# bug_entry::line\n"
 #else
-#define __BUGVERBOSE_LOCATION(file, line)			\
-		.pushsection .rodata.str, "aMS", @progbits, 1;	\
-		.align 2;					\
-	10002:	.ascii file "\0";				\
-		.popsection;					\
-								\
-		.long 10002b - .;				\
-		.short line;
-#define _BUGVERBOSE_LOCATION(file, line) __BUGVERBOSE_LOCATION(file, line)
+#define __BUG_ENTRY_VERBOSE(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));		\
+#define __BUG_ASM(cond_str, flags)					\
+do {									\
+	asm_inline volatile("\n"					\
+		"0:	mc	0,0\n"					\
+		"	.section __bug_table,\"aw\"\n"			\
+		"1:	.long	0b - .	# bug_entry::bug_addr\n"	\
+		__BUG_ENTRY_VERBOSE("%[file]", "%[line]")		\
+		"	.short	%[flgs]	# bug_entry::flags\n"		\
+		"	.org	1b+%[size]\n"				\
+		"	.previous"					\
+		:							\
+		: [file] "i" (WARN_CONDITION_STR(cond_str) __FILE__),	\
+		  [line] "i" (__LINE__),				\
+		  [flgs] "i" (flags),					\
+		  [size] "i" (sizeof(struct bug_entry)));		\
 } while (0)
 
-#define BUG()							\
-do {								\
-	__BUG_FLAGS("", 0);					\
-	unreachable();						\
+#define BUG()								\
+do {									\
+	__BUG_ASM("", 0);						\
+	unreachable();							\
+} while (0)
+
+#define __WARN_FLAGS(cond_str, flags)					\
+do {									\
+	__BUG_ASM(cond_str, BUGFLAG_WARNING | (flags));			\
 } while (0)
 
 #define HAVE_ARCH_BUG
-- 
2.51.0