Subject: Re: [PATCH 2/4] ppc32/kprobe: introduce copy_exc_stack

From: Benjamin Herrenschmidt <[email-masked]>
Date: Tue, 13 Dec 2011 10:01:11 +1100

On Mon, 2011-12-12 at 16:50 +0800, Tiejun Chen wrote:
> We need a copy mechanism to migrate exception stack. But looks copy_page()
> already implement this well so we can complete copy_exc_stack() based on
> that directly.

I'd rather you don't hijack copy_page which is quite sensitive. The
emulation isn't performance critical so a "dumber" routine would work
fine.

Why not use memcpy ? You can call it from assembly.

Cheers,
Ben.

> Signed-off-by: Tiejun Chen <[email-masked]>
> ---
>  arch/powerpc/include/asm/page_32.h |    1 +
>  arch/powerpc/kernel/misc_32.S      |   16 +++++++++++++++-
>  arch/powerpc/kernel/ppc_ksyms.c    |    1 +
>  3 files changed, 17 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/page_32.h b/arch/powerpc/include/asm/page_32.h
> index 68d73b2..2c1fd84 100644
> --- a/arch/powerpc/include/asm/page_32.h
> +++ b/arch/powerpc/include/asm/page_32.h
> @@ -40,6 +40,7 @@ struct page;
>  extern void clear_pages(void *page, int order);
>  static inline void clear_page(void *page) { clear_pages(page, 0); }
>  extern void copy_page(void *to, void *from);
> +extern void copy_exc_stack(void *to, void *from);
>  
>  #include <asm-generic/getorder.h>
>  
> diff --git a/arch/powerpc/kernel/misc_32.S b/arch/powerpc/kernel/misc_32.S
> index 998a100..aa02545 100644
> --- a/arch/powerpc/kernel/misc_32.S
> +++ b/arch/powerpc/kernel/misc_32.S
> @@ -527,7 +527,7 @@ _GLOBAL(clear_pages)
>  	stw	r8,12(r3);	\
>  	stwu	r9,16(r3)
>  
> -_GLOBAL(copy_page)
> +ready_copy:
>  	addi	r3,r3,-4
>  	addi	r4,r4,-4
>  
> @@ -544,7 +544,21 @@ _GLOBAL(copy_page)
>  	dcbt	r5,r4
>  	li	r11,L1_CACHE_BYTES+4
>  #endif /* MAX_COPY_PREFETCH */
> +	blr
> +
> +_GLOBAL(copy_exc_stack)
> +	mflr	r12
> +	bl	ready_copy
> +	mtlr	r12
> +	li	r0,INT_FRAME_SIZE/L1_CACHE_BYTES - MAX_COPY_PREFETCH
> +	b	go_copy
> +
> +_GLOBAL(copy_page)
> +	mflr	r12
> +	bl	ready_copy
> +	mtlr	r12
>  	li	r0,PAGE_SIZE/L1_CACHE_BYTES - MAX_COPY_PREFETCH
> +go_copy:
>  	crclr	4*cr0+eq
>  2:
>  	mtctr	r0
> diff --git a/arch/powerpc/kernel/ppc_ksyms.c b/arch/powerpc/kernel/ppc_ksyms.c
> index f5ae872..2223daf 100644
> --- a/arch/powerpc/kernel/ppc_ksyms.c
> +++ b/arch/powerpc/kernel/ppc_ksyms.c
> @@ -88,6 +88,7 @@ EXPORT_SYMBOL(__clear_user);
>  EXPORT_SYMBOL(__strncpy_from_user);
>  EXPORT_SYMBOL(__strnlen_user);
>  EXPORT_SYMBOL(copy_page);
> +EXPORT_SYMBOL(copy_exc_stack);
>  
>  #if defined(CONFIG_PCI) && defined(CONFIG_PPC32)
>  EXPORT_SYMBOL(isa_io_base);