linux-kernel - [RFC 1/8] x86: Provide assembly __bug

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Message-ID: <20250602144755.319275437@infradead.org>
Date: Mon, 02 Jun 2025 16:42:02 +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: [RFC 1/8] x86: Provide assembly __bug_table helpers

Rework the __bug_table helpers such that usage from assembly becomes
possible.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/bug.h |   54 ++++++++++++++++++++-------------------------
 1 file changed, 24 insertions(+), 30 deletions(-)

--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -32,46 +32,40 @@
 #ifdef CONFIG_GENERIC_BUG
 
 #ifdef CONFIG_X86_32
-# define __BUG_REL(val)	".long " __stringify(val)
+#define ASM_BUG_REL(val)	.long val
 #else
-# define __BUG_REL(val)	".long " __stringify(val) " - ."
+#define ASM_BUG_REL(val)	.long val - .
 #endif
 
 #ifdef CONFIG_DEBUG_BUGVERBOSE
+#define ASM_BUGTABLE_VERBOSE(file, line)				\
+	ASM_BUG_REL(file) ;						\
+	.word line
+#define ASM_BUGTABLE_VERBOSE_SIZE	6 /* sizeof(file) + sizeof(line) */
+#else
+#define ASM_BUGTABLE_VERBOSE(file, line)
+#define ASM_BUGTABLE_VERBOSE_SIZE	0
+#endif
 
-#define _BUG_FLAGS(ins, flags, extra)					\
-do {									\
-	asm_inline volatile("1:\t" ins "\n"				\
-		     ".pushsection __bug_table,\"aw\"\n"		\
-		     "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n"	\
-		     "\t"  __BUG_REL(%c0) "\t# bug_entry::file\n"	\
-		     "\t.word %c1"        "\t# bug_entry::line\n"	\
-		     "\t.word %c2"        "\t# bug_entry::flags\n"	\
-		     "\t.org 2b+%c3\n"					\
-		     ".popsection\n"					\
-		     extra						\
-		     : : "i" (__FILE__), "i" (__LINE__),		\
-			 "i" (flags),					\
-			 "i" (sizeof(struct bug_entry)));		\
-} while (0)
+#define ASM_BUGTABLE_BASE_SIZE		6 /* sizeof(bug_addr) + sizeof(flags) */
 
-#else /* !CONFIG_DEBUG_BUGVERBOSE */
+#define ASM_BUGTABLE_FLAGS(at, file, line, flags)			\
+	.pushsection __bug_table, "aw" ;				\
+	123:	ASM_BUG_REL(at) ;					\
+	ASM_BUGTABLE_VERBOSE(file, line) ;				\
+	.word	flags ;							\
+	.org 123b + ASM_BUGTABLE_BASE_SIZE + ASM_BUGTABLE_VERBOSE_SIZE ;\
+	.popsection
 
-#define _BUG_FLAGS(ins, flags, extra)					\
+#define _BUG_FLAGS(insn, flags, extra)					\
 do {									\
-	asm_inline volatile("1:\t" ins "\n"				\
-		     ".pushsection __bug_table,\"aw\"\n"		\
-		     "2:\t" __BUG_REL(1b) "\t# bug_entry::bug_addr\n"	\
-		     "\t.word %c0"        "\t# bug_entry::flags\n"	\
-		     "\t.org 2b+%c1\n"					\
-		     ".popsection\n"					\
-		     extra						\
-		     : : "i" (flags),					\
-			 "i" (sizeof(struct bug_entry)));		\
+	asm_inline volatile("1:\t" insn "\n"				\
+	    __stringify(ASM_BUGTABLE_FLAGS(1b, %c[file], %c[line], %c[fl])) "\n" \
+			    extra					\
+		     : : [file] "i" (__FILE__), [line] "i" (__LINE__),	\
+			 [fl] "i" (flags));				\
 } while (0)
 
-#endif /* CONFIG_DEBUG_BUGVERBOSE */
-
 #else
 
 #define _BUG_FLAGS(ins, flags, extra)  asm volatile(ins)