Re: [PATCH] bug: Use normal relative pointers in 'struct bug_entry'

[Michael Ellerman]

Josh Poimboeuf <jpoimboe@xxxxxxxxxx> writes:
> 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@xxxxxxxxxx>
> ---
...
> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
> index ecbae1832de3..76252576d889 100644
> --- a/arch/powerpc/include/asm/bug.h
> +++ b/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

Embarrassingly, we have another copy of the logic, used in the C
versions, they need updating too:

diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
index ecbae1832de3..3fde35fd67f8 100644
--- a/arch/powerpc/include/asm/bug.h
+++ b/arch/powerpc/include/asm/bug.h
@@ -49,14 +49,14 @@
 #ifdef CONFIG_DEBUG_BUGVERBOSE
 #define _EMIT_BUG_ENTRY				\
 	".section __bug_table,\"aw\"\n"		\
-	"2:\t.4byte 1b - 2b, %0 - 2b\n"		\
+	"2:\t.4byte 1b - ., %0 - .\n"		\
 	"\t.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:\t.4byte 1b - .\n"			\
 	"\t.short %2\n"				\
 	".org 2b+%3\n"				\
 	".previous\n"


With that added it seems to be working correctly for me.

Acked-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> (powerpc)


cheers