bug: Use normal relative pointers in 'struct bug_entry'

With CONFIG_GENERIC_BUG_RELATIVE_POINTERS, the addr/file relative
pointers are calculated weirdly: based on the beginning of the bug_entry
struct address, rather than their respective pointer addresses.

Make the relative pointers less surprising to both humans and tools by
calculating them the normal way.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Sven Schnelle <svens@linux.ibm.com> # s390
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com> [arm64]
Link: https://lkml.kernel.org/r/f0e05be797a16f4fc2401eeb88c8450dcbe61df6.1652362951.git.jpoimboe@kernel.org

arch/arm64/include/asm/asm-bug.h

@@ -14,7 +14,7 @@
 	14472:	.string file;					\
 		.popsection;					\
 								\
-		.long 14472b - 14470b;				\
+		.long 14472b - .;				\
 		.short line;
 #else
 #define _BUGVERBOSE_LOCATION(file, line)
@@ -25,7 +25,7 @@
 #define __BUG_ENTRY(flags) 				\
 		.pushsection __bug_table,"aw";		\
 		.align 2;				\
-	14470:	.long 14471f - 14470b;			\
+	14470:	.long 14471f - .;			\
 _BUGVERBOSE_LOCATION(__FILE__, __LINE__)		\
 		.short flags; 				\
 		.popsection;				\

arch/powerpc/include/asm/bug.h

@@ -13,7 +13,8 @@
 #ifdef CONFIG_DEBUG_BUGVERBOSE
 .macro __EMIT_BUG_ENTRY addr,file,line,flags
 	 .section __bug_table,"aw"
-5001:	 .4byte \addr - 5001b, 5002f - 5001b
+5001:	 .4byte \addr - .
+	 .4byte 5002f - .
 	 .short \line, \flags
 	 .org 5001b+BUG_ENTRY_SIZE
 	 .previous
@@ -24,7 +25,7 @@
 #else
 .macro __EMIT_BUG_ENTRY addr,file,line,flags
 	 .section __bug_table,"aw"
-5001:	 .4byte \addr - 5001b
+5001:	 .4byte \addr - .
 	 .short \flags
 	 .org 5001b+BUG_ENTRY_SIZE
 	 .previous
@@ -49,15 +50,16 @@
 #ifdef CONFIG_DEBUG_BUGVERBOSE
 #define _EMIT_BUG_ENTRY				\
 	".section __bug_table,\"aw\"\n"		\
-	"2:\t.4byte 1b - 2b, %0 - 2b\n"		\
+	"2:	.4byte 1b - .\n"		\
-	"\t.short %1, %2\n"			\
+	"	.4byte %0 - .\n"		\
+	"	.short %1, %2\n"		\
 	".org 2b+%3\n"				\
 	".previous\n"
 #else
 #define _EMIT_BUG_ENTRY				\
 	".section __bug_table,\"aw\"\n"		\
-	"2:\t.4byte 1b - 2b\n"			\
+	"2:	.4byte 1b - .\n"		\
-	"\t.short %2\n"				\
+	"	.short %2\n"			\
 	".org 2b+%3\n"				\
 	".previous\n"
 #endif

arch/riscv/include/asm/bug.h

@@ -30,8 +30,8 @@
 typedef u32 bug_insn_t;
 
 #ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
-#define __BUG_ENTRY_ADDR	RISCV_INT " 1b - 2b"
+#define __BUG_ENTRY_ADDR	RISCV_INT " 1b - ."
-#define __BUG_ENTRY_FILE	RISCV_INT " %0 - 2b"
+#define __BUG_ENTRY_FILE	RISCV_INT " %0 - ."
 #else
 #define __BUG_ENTRY_ADDR	RISCV_PTR " 1b"
 #define __BUG_ENTRY_FILE	RISCV_PTR " %0"

arch/s390/include/asm/bug.h

@@ -15,7 +15,8 @@
 		"1:	.asciz	\""__FILE__"\"\n"		\
 		".previous\n"					\
 		".section __bug_table,\"awM\",@progbits,%2\n"	\
-		"2:	.long	0b-2b,1b-2b\n"			\
+		"2:	.long	0b-.\n"				\
+		"	.long	1b-.\n"				\
 		"	.short	%0,%1\n"			\
 		"	.org	2b+%2\n"			\
 		".previous\n"					\
@@ -30,7 +31,7 @@
 	asm_inline volatile(					\
 		"0:	mc	0,0\n"				\
 		".section __bug_table,\"awM\",@progbits,%1\n"	\
-		"1:	.long	0b-1b\n"			\
+		"1:	.long	0b-.\n"				\
 		"	.short	%0\n"				\
 		"	.org	1b+%1\n"			\
 		".previous\n"					\

arch/x86/include/asm/bug.h

@@ -18,7 +18,7 @@
 #ifdef CONFIG_X86_32
 # define __BUG_REL(val)	".long " __stringify(val)
 #else
-# define __BUG_REL(val)	".long " __stringify(val) " - 2b"
+# define __BUG_REL(val)	".long " __stringify(val) " - ."
 #endif
 
 #ifdef CONFIG_DEBUG_BUGVERBOSE

lib/bug.c

@@ -6,8 +6,7 @@
 
   CONFIG_BUG - emit BUG traps.  Nothing happens without this.
   CONFIG_GENERIC_BUG - enable this code.
-  CONFIG_GENERIC_BUG_RELATIVE_POINTERS - use 32-bit pointers relative to
+  CONFIG_GENERIC_BUG_RELATIVE_POINTERS - use 32-bit relative pointers for bug_addr and file
-	the containing struct bug_entry for bug_addr and file.
   CONFIG_DEBUG_BUGVERBOSE - emit full file+line information for each BUG
 
   CONFIG_BUG and CONFIG_DEBUG_BUGVERBOSE are potentially user-settable
@@ -53,10 +52,10 @@ extern struct bug_entry __start___bug_table[], __stop___bug_table[];
 
 static inline unsigned long bug_addr(const struct bug_entry *bug)
 {
-#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
+#ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
-	return bug->bug_addr;
+	return (unsigned long)&bug->bug_addr_disp + bug->bug_addr_disp;
 #else
-	return (unsigned long)bug + bug->bug_addr_disp;
+	return bug->bug_addr;
 #endif
 }
 
@@ -131,10 +130,10 @@ void bug_get_file_line(struct bug_entry *bug, const char **file,
 		       unsigned int *line)
 {
 #ifdef CONFIG_DEBUG_BUGVERBOSE
-#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
+#ifdef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
-	*file = bug->file;
+	*file = (const char *)&bug->file_disp + bug->file_disp;
 #else
-	*file = (const char *)bug + bug->file_disp;
+	*file = bug->file;
 #endif
 	*line = bug->line;
 #else