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Date: Mon, 14 Dec 2015 11:30:27 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Borislav Petkov <bp@...en8.de>
Cc: LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ftrace: Kill ftrace_caller_end label
On Mon, 14 Dec 2015 17:08:34 +0100
Borislav Petkov <bp@...en8.de> wrote:
> From: Borislav Petkov <bp@...e.de>
>
> One of ftrace_caller_and and ftrace_return is redundant so unify them.
s/_and/_end/
> Rename ftrace_return to ftrace_epilogue to mean that everything after
> that label represents, like an afterword, work which happens *after* the
> ftrace call, e.g., the function graph tracer for one.
>
> Beef up the comment about the code contents and layout before
> ftrace_epilogue label.
According to http://www.thefreedictionary.com/epilog
ep·i·logue also ep·i·log (ĕp′ə-lôg′, -lŏg′) (n).
1.
a. A short poem or speech spoken directly to the audience following
the conclusion of a play.
Hmm, that doesn't fit.
b. The performer who delivers such a short poem or speech.
Maybe people can think ftrace as a poem. But people will never think
that I give such a short speech.
2. A short addition or concluding section at the end of a literary
work, often dealing with the future of its characters. Also called
afterword.
Ah, "afterword" also doesn't fit, unless you mean "characters" as a set
of "char []". Which I guess the trampoline would fit.
3. An event which reflects meaningfully on a recently ended conflict or
struggle.
Ah! This looks like the best match! Thus, this should be stated in the
changelog!
>
> Signed-off-by: Borislav Petkov <bp@...e.de>
> Cc: Steven Rostedt <rostedt@...dmis.org>
Reviewed-by: Steven Rostedt <rostedt@...dmis.org>
-- Steve
> ---
> arch/x86/kernel/ftrace.c | 11 +++++------
> arch/x86/kernel/mcount_64.S | 14 ++++++++------
> 2 files changed, 13 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
> index 311bcf338f07..26ad092ac0dc 100644
> --- a/arch/x86/kernel/ftrace.c
> +++ b/arch/x86/kernel/ftrace.c
> @@ -690,9 +690,8 @@ static inline void tramp_free(void *tramp) { }
> #endif
>
> /* Defined as markers to the end of the ftrace default trampolines */
> -extern void ftrace_caller_end(void);
> extern void ftrace_regs_caller_end(void);
> -extern void ftrace_return(void);
> +extern void ftrace_epilogue(void);
> extern void ftrace_caller_op_ptr(void);
> extern void ftrace_regs_caller_op_ptr(void);
>
> @@ -739,7 +738,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
> op_offset = (unsigned long)ftrace_regs_caller_op_ptr;
> } else {
> start_offset = (unsigned long)ftrace_caller;
> - end_offset = (unsigned long)ftrace_caller_end;
> + end_offset = (unsigned long)ftrace_epilogue;
> op_offset = (unsigned long)ftrace_caller_op_ptr;
> }
>
> @@ -747,7 +746,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
>
> /*
> * Allocate enough size to store the ftrace_caller code,
> - * the jmp to ftrace_return, as well as the address of
> + * the jmp to ftrace_epilogue, as well as the address of
> * the ftrace_ops this trampoline is used for.
> */
> trampoline = alloc_tramp(size + MCOUNT_INSN_SIZE + sizeof(void *));
> @@ -765,8 +764,8 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size)
>
> ip = (unsigned long)trampoline + size;
>
> - /* The trampoline ends with a jmp to ftrace_return */
> - jmp = ftrace_jmp_replace(ip, (unsigned long)ftrace_return);
> + /* The trampoline ends with a jmp to ftrace_epilogue */
> + jmp = ftrace_jmp_replace(ip, (unsigned long)ftrace_epilogue);
> memcpy(trampoline + size, jmp, MCOUNT_INSN_SIZE);
>
> /*
> diff --git a/arch/x86/kernel/mcount_64.S b/arch/x86/kernel/mcount_64.S
> index 87e1762e2bca..ed48a9f465f8 100644
> --- a/arch/x86/kernel/mcount_64.S
> +++ b/arch/x86/kernel/mcount_64.S
> @@ -168,12 +168,14 @@ GLOBAL(ftrace_call)
> restore_mcount_regs
>
> /*
> - * The copied trampoline must call ftrace_return as it
> + * The copied trampoline must call ftrace_epilogue as it
> * still may need to call the function graph tracer.
> + *
> + * The code up to this label is copied into trampolines so
> + * think twice before adding any new code or changing the
> + * layout here.
> */
> -GLOBAL(ftrace_caller_end)
> -
> -GLOBAL(ftrace_return)
> +GLOBAL(ftrace_epilogue)
>
> #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> GLOBAL(ftrace_graph_call)
> @@ -244,14 +246,14 @@ GLOBAL(ftrace_regs_call)
> popfq
>
> /*
> - * As this jmp to ftrace_return can be a short jump
> + * As this jmp to ftrace_epilogue can be a short jump
> * it must not be copied into the trampoline.
> * The trampoline will add the code to jump
> * to the return.
> */
> GLOBAL(ftrace_regs_caller_end)
>
> - jmp ftrace_return
> + jmp ftrace_epilogue
>
> END(ftrace_regs_caller)
>
--
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