arm64: add architecture specified current_pt_regs

Commit Message

Zhi-zhou Zhang Feb. 18, 2016, 11:48 a.m. UTC

From: zhizhou <[e-mail]>

This patch is based on the implementation of arm. The generic
current_pt_regs is implemented with current->stack. It need to access
memory that would be too expensive.

Signed-off-by: zhizhou <[e-mail]>
---
 arch/arm64/include/asm/ptrace.h | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Catalin Marinas Feb. 18, 2016, 11:58 a.m. UTC | #1

On Thu, Feb 18, 2016 at 07:48:35PM +0800, Zhi-zhou Zhang wrote:
> From: zhizhou <[e-mail]>
> 
> This patch is based on the implementation of arm. The generic
> current_pt_regs is implemented with current->stack. It need to access
> memory that would be too expensive.

Do you have any performance numbers?

> diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
> index e9e5467..1865d54 100644
> --- a/arch/arm64/include/asm/ptrace.h
> +++ b/arch/arm64/include/asm/ptrace.h
> @@ -185,5 +185,9 @@ static inline int valid_user_regs(struct user_pt_regs *regs)
>  
>  extern unsigned long profile_pc(struct pt_regs *regs);
>  
> +#define current_pt_regs(void) ({ (struct pt_regs *)			\
> +	((current_stack_pointer | (THREAD_SIZE - 1)) - 0xf) - 1;	\
> +})

I don't think this works well with the separate IRQ stack that we merged
in 4.5-rc1. current_thread_info() explicitly uses "sp_el0" while
current_stack_pointer is just "sp" (though I don't think we ever use
current_pt_regs in interrupt context).

Patch

diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
index e9e5467..1865d54 100644
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -185,5 +185,9 @@  static inline int valid_user_regs(struct user_pt_regs *regs)
 
 extern unsigned long profile_pc(struct pt_regs *regs);
 
+#define current_pt_regs(void) ({ (struct pt_regs *)			\
+	((current_stack_pointer | (THREAD_SIZE - 1)) - 0xf) - 1;	\
+})
+
 #endif /* __ASSEMBLY__ */
 #endif