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    SubjectRe: Re: [RFC PATCH 4/4] ftrace/x86: Add support for -mfentry to x86_64
    (2012/08/09 22:46), Steven Rostedt wrote:
    > Peter and Masami
    >
    > During my final tests, I found that this change breaks the
    > !DYNAMIC_FTRACE config. That is, when we don't do the run-time updates
    > of mcount calls to nops, the compiler will use fentry but the code still
    > uses mcount.

    Ah, right. we have to take care about it.

    >
    > I fixed this in the patch below. But as you two have acked and reviewed
    > it, I can't add your tags if I have changed the code. Can you ack/review
    > it again.

    This looks good for me.

    Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

    >
    > Thanks!
    >
    > -- Steve
    >
    >
    > On Tue, 2012-08-07 at 15:38 -0400, Steven Rostedt wrote:
    >> From: Steven Rostedt <srostedt@redhat.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.
    >>
    >> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    >> Cc: Andi Kleen <andi@firstfloor.org>
    >> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    >
    > (change log kept the same)
    >
    > 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..a698521 100644
    > --- a/arch/x86/kernel/entry_64.S
    > +++ b/arch/x86/kernel/entry_64.S
    > @@ -68,10 +68,18 @@
    > .section .entry.text, "ax"
    >
    > #ifdef CONFIG_FUNCTION_TRACER
    > +
    > +#ifdef CC_USING_FENTRY
    > +# define function_hook __fentry__
    > +#else
    > +# define function_hook mcount
    > +#endif
    > +
    > #ifdef CONFIG_DYNAMIC_FTRACE
    > -ENTRY(mcount)
    > +
    > +ENTRY(function_hook)
    > retq
    > -END(mcount)
    > +END(function_hook)
    >
    > /* skip is set if stack has been adjusted */
    > .macro ftrace_caller_setup skip=0
    > @@ -84,7 +92,11 @@ 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)
    > @@ -177,7 +189,8 @@ END(ftrace_regs_caller)
    >
    >
    > #else /* ! CONFIG_DYNAMIC_FTRACE */
    > -ENTRY(mcount)
    > +
    > +ENTRY(function_hook)
    > cmpl $0, function_trace_stop
    > jne ftrace_stub
    >
    > @@ -199,7 +212,11 @@ trace:
    > MCOUNT_SAVE_FRAME
    >
    > movq RIP(%rsp), %rdi
    > +#ifdef CC_USING_FENTRY
    > + movq SS+16(%rsp), %rsi
    > +#else
    > movq 8(%rbp), %rsi
    > +#endif
    > subq $MCOUNT_INSN_SIZE, %rdi
    >
    > call *ftrace_trace_function
    > @@ -207,7 +224,7 @@ trace:
    > MCOUNT_RESTORE_FRAME
    >
    > jmp ftrace_stub
    > -END(mcount)
    > +END(function_hook)
    > #endif /* CONFIG_DYNAMIC_FTRACE */
    > #endif /* CONFIG_FUNCTION_TRACER */
    >
    > @@ -215,9 +232,14 @@ 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);
    >
    >
    > --
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    >


    --
    Masami HIRAMATSU
    Software Platform Research Dept. Linux Technology Center
    Hitachi, Ltd., Yokohama Research Laboratory
    E-mail: masami.hiramatsu.pt@hitachi.com




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