[PATCH] powerpc: Allow relative pointers in bug table entries

[Christophe Leroy]

Le 27/11/2020 à 04:02, Jordan Niethe a écrit :
> This enables GENERIC_BUG_RELATIVE_POINTERS on Power so that 32-bit
> offsets are stored in the bug entries rather than 64-bit pointers.
> 
> Signed-off-by: Jordan Niethe <jniethe5 at gmail.com>
> ---
>   arch/powerpc/Kconfig           |  4 ++++
>   arch/powerpc/include/asm/bug.h | 37 ++++++++++++++++++++++++++++++++--
>   arch/powerpc/xmon/xmon.c       | 17 ++++++++++++++--
>   3 files changed, 54 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index e9f13fe08492..294108e0e5c6 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -311,6 +311,10 @@ config GENERIC_BUG
>   	default y
>   	depends on BUG
>   
> +config GENERIC_BUG_RELATIVE_POINTERS
> +	def_bool y
> +	depends on GENERIC_BUG
> +
>   config SYS_SUPPORTS_APM_EMULATION
>   	default y if PMAC_APM_EMU
>   	bool
> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
> index 338f36cd9934..d03d834042a1 100644
> --- a/arch/powerpc/include/asm/bug.h
> +++ b/arch/powerpc/include/asm/bug.h
> @@ -12,7 +12,11 @@
>   #ifdef CONFIG_DEBUG_BUGVERBOSE
>   .macro EMIT_BUG_ENTRY addr,file,line,flags
>   	 .section __bug_table,"aw"
> +#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS

As far as I understand, as soon as CONFIG_BUG is selected, GENERIC_BUG is automatically selected so 
GENERIC_BUG_RELATIVE_POINTERS is selected as well. Therefore this #ifndef is never possible.

>   5001:	 PPC_LONG \addr, 5002f
> +#else
> +5001:	 .4byte \addr - 5001b, 5002f - 5001b
> +#endif /* CONFIG_GENERIC_BUG_RELATIVE_POINTERS */
>   	 .short \line, \flags
>   	 .org 5001b+BUG_ENTRY_SIZE
>   	 .previous
> @@ -23,7 +27,11 @@
>   #else
>   .macro EMIT_BUG_ENTRY addr,file,line,flags
>   	 .section __bug_table,"aw"
> +#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS

Same

>   5001:	 PPC_LONG \addr
> +#else
> +5001:	 .4byte \addr - 5001b
> +#endif /* CONFIG_GENERIC_BUG_RELATIVE_POINTERS */
>   	 .short \flags
>   	 .org 5001b+BUG_ENTRY_SIZE
>   	 .previous
> @@ -34,20 +42,45 @@
>   /* _EMIT_BUG_ENTRY expects args %0,%1,%2,%3 to be FILE, LINE, flags and
>      sizeof(struct bug_entry), respectively */
>   #ifdef CONFIG_DEBUG_BUGVERBOSE
> +#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS

Same

>   #define _EMIT_BUG_ENTRY				\
>   	".section __bug_table,\"aw\"\n"		\
>   	"2:\t" PPC_LONG "1b, %0\n"		\
>   	"\t.short %1, %2\n"			\
>   	".org 2b+%3\n"				\
>   	".previous\n"
> -#else
> +
> +#else /* relative pointers */
> +
> +#define _EMIT_BUG_ENTRY				\
> +	".section __bug_table,\"aw\"\n"		\
> +	"2:\t.4byte 1b - 2b, %0 - 2b\n"		\
> +	"\t.short %1, %2\n"			\
> +	".org 2b+%3\n"				\
> +	".previous\n"
> +#endif /* relative pointers */
> +
> +#else /* verbose */
> +
> +#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS

Same

>   #define _EMIT_BUG_ENTRY				\
>   	".section __bug_table,\"aw\"\n"		\
>   	"2:\t" PPC_LONG "1b\n"			\
>   	"\t.short %2\n"				\
>   	".org 2b+%3\n"				\
>   	".previous\n"
> -#endif
> +
> +#else /* relative pointers */
> +
> +#define _EMIT_BUG_ENTRY				\
> +	".section __bug_table,\"aw\"\n"		\
> +	"2:\t.4byte 1b - 2b\n"		\
> +	"\t.short %2\n"				\
> +	".org 2b+%3\n"				\
> +	".previous\n"
> +
> +#endif /* relative pointers */
> +#endif /* verbose */
>   
>   #define BUG_ENTRY(insn, flags, ...)			\
>   	__asm__ __volatile__(				\
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index 55c43a6c9111..5f7cf7e95767 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -1731,6 +1731,9 @@ static void print_bug_trap(struct pt_regs *regs)
>   #ifdef CONFIG_BUG
>   	const struct bug_entry *bug;
>   	unsigned long addr;
> +#ifdef CONFIG_DEBUG_BUGVERBOSE
> +	char *file;
> +#endif
>   
>   	if (regs->msr & MSR_PR)
>   		return;		/* not in kernel */
> @@ -1744,10 +1747,20 @@ static void print_bug_trap(struct pt_regs *regs)
>   		return;
>   
>   #ifdef CONFIG_DEBUG_BUGVERBOSE
> +#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS

Same

> +	file = bug->file;
> +#else /* relative pointers */
> +	file = (char *)bug + bug->file_disp;
> +#endif /* relative pointers */
>   	printf("kernel BUG at %s:%u!\n",
> -	       bug->file, bug->line);
> +	       file, bug->line);
>   #else
> -	printf("kernel BUG at %px!\n", (void *)bug->bug_addr);
> +#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS

Same

> +	addr = bug->addr;
> +#else /* relative pointers */
> +	addr = (unsigned long)bug + bug->bug_addr_disp;
> +#endif /* relative pointers */
> +	printf("kernel BUG at %px!\n", (void *)addr);
>   #endif
>   #endif /* CONFIG_BUG */
>   }
> 

Christophe