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Date: Thu, 09 Aug 2012 17:34:22 +0900
From: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Frederic Weisbecker <fweisbec@...il.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andi Kleen <andi@...stfloor.org>
Subject: Re: [RFC PATCH 4/4] ftrace/x86: Add support for -mfentry to x86_64
(2012/08/08 4:38), Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@...hat.com>
>
> If the kernel is compiled with gcc 4.6.0 which supports -mfentry,
> then use that instead of mcount.
>
> With mcount, frame pointers are forced with the -pg option and we
> get something like:
>
> <can_vma_merge_before>:
> 55 push %rbp
> 48 89 e5 mov %rsp,%rbp
> 53 push %rbx
> 41 51 push %r9
> e8 fe 6a 39 00 callq ffffffff81483d00 <mcount>
> 31 c0 xor %eax,%eax
> 48 89 fb mov %rdi,%rbx
> 48 89 d7 mov %rdx,%rdi
> 48 33 73 30 xor 0x30(%rbx),%rsi
> 48 f7 c6 ff ff ff f7 test $0xfffffffff7ffffff,%rsi
>
> With -mfentry, frame pointers are no longer forced and the call looks
> like this:
>
> <can_vma_merge_before>:
> e8 33 af 37 00 callq ffffffff81461b40 <__fentry__>
> 53 push %rbx
> 48 89 fb mov %rdi,%rbx
> 31 c0 xor %eax,%eax
> 48 89 d7 mov %rdx,%rdi
> 41 51 push %r9
> 48 33 73 30 xor 0x30(%rbx),%rsi
> 48 f7 c6 ff ff ff f7 test $0xfffffffff7ffffff,%rsi
>
> This adds the ftrace hook at the beginning of the function before a
> frame is set up, and allows the function callbacks to be able to access
> parameters. As kprobes now can use function tracing (at least on x86)
> this speeds up the kprobe hooks that are at the beginning of the
> function.
This looks good for me:)
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Thanks!
>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Cc: Andi Kleen <andi@...stfloor.org>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
> arch/x86/Kconfig | 1 +
> arch/x86/include/asm/ftrace.h | 7 ++++++-
> arch/x86/kernel/entry_64.S | 18 +++++++++++++++++-
> arch/x86/kernel/x8664_ksyms_64.c | 6 +++++-
> 4 files changed, 29 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index c70684f..bbbf5d8 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -36,6 +36,7 @@ config X86
> select HAVE_KRETPROBES
> select HAVE_OPTPROBES
> select HAVE_FTRACE_MCOUNT_RECORD
> + select HAVE_FENTRY if X86_64
> select HAVE_C_RECORDMCOUNT
> select HAVE_DYNAMIC_FTRACE
> select HAVE_FUNCTION_TRACER
> diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
> index a6cae0c..9a25b52 100644
> --- a/arch/x86/include/asm/ftrace.h
> +++ b/arch/x86/include/asm/ftrace.h
> @@ -35,7 +35,11 @@
> #endif
>
> #ifdef CONFIG_FUNCTION_TRACER
> -#define MCOUNT_ADDR ((long)(mcount))
> +#ifdef CC_USING_FENTRY
> +# define MCOUNT_ADDR ((long)(__fentry__))
> +#else
> +# define MCOUNT_ADDR ((long)(mcount))
> +#endif
> #define MCOUNT_INSN_SIZE 5 /* sizeof mcount call */
>
> #ifdef CONFIG_DYNAMIC_FTRACE
> @@ -46,6 +50,7 @@
> #ifndef __ASSEMBLY__
> extern void mcount(void);
> extern atomic_t modifying_ftrace_code;
> +extern void __fentry__(void);
>
> static inline unsigned long ftrace_call_adjust(unsigned long addr)
> {
> diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
> index 38308fa..2add3bb 100644
> --- a/arch/x86/kernel/entry_64.S
> +++ b/arch/x86/kernel/entry_64.S
> @@ -69,9 +69,16 @@
>
> #ifdef CONFIG_FUNCTION_TRACER
> #ifdef CONFIG_DYNAMIC_FTRACE
> +
> +#ifdef CC_USING_FENTRY
> +ENTRY(__fentry__)
> + retq
> +END(__fentry__)
> +#else
> ENTRY(mcount)
> retq
> END(mcount)
> +#endif
>
> /* skip is set if stack has been adjusted */
> .macro ftrace_caller_setup skip=0
> @@ -84,7 +91,11 @@ END(mcount)
> movq RIP(%rsp), %rdi
> subq $MCOUNT_INSN_SIZE, %rdi
> /* Load the parent_ip into the second parameter */
> +#ifdef CC_USING_FENTRY
> + movq SS+16(%rsp), %rsi
> +#else
> movq 8(%rbp), %rsi
> +#endif
> .endm
>
> ENTRY(ftrace_caller)
> @@ -215,9 +226,14 @@ END(mcount)
> ENTRY(ftrace_graph_caller)
> MCOUNT_SAVE_FRAME
>
> +#ifdef CC_USING_FENTRY
> + leaq SS+16(%rsp), %rdi
> + movq $0, %rdx /* No framepointers needed */
> +#else
> leaq 8(%rbp), %rdi
> - movq RIP(%rsp), %rsi
> movq (%rbp), %rdx
> +#endif
> + movq RIP(%rsp), %rsi
> subq $MCOUNT_INSN_SIZE, %rsi
>
> call prepare_ftrace_return
> diff --git a/arch/x86/kernel/x8664_ksyms_64.c b/arch/x86/kernel/x8664_ksyms_64.c
> index 9796c2f..643b236 100644
> --- a/arch/x86/kernel/x8664_ksyms_64.c
> +++ b/arch/x86/kernel/x8664_ksyms_64.c
> @@ -13,9 +13,13 @@
> #include <asm/ftrace.h>
>
> #ifdef CONFIG_FUNCTION_TRACER
> -/* mcount is defined in assembly */
> +/* mcount and __fentry__ are defined in assembly */
> +#ifdef CC_USING_FENTRY
> +EXPORT_SYMBOL(__fentry__);
> +#else
> EXPORT_SYMBOL(mcount);
> #endif
> +#endif
>
> EXPORT_SYMBOL(__get_user_1);
> EXPORT_SYMBOL(__get_user_2);
>
--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com
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