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SubjectRe: [PATCH] arm64/ftrace: Make function graph use ftrace directly
On Tue, Feb 22, 2022 at 09:00:49PM +0800, Chengming Zhou wrote:
> As we do in commit 0c0593b45c9b ("x86/ftrace: Make function graph
> use ftrace directly"), we don't need special hook for graph tracer,
> but instead we use graph_ops:func function to install return_hooker.
>
> Since commit 3b23e4991fb6 ("arm64: implement ftrace with regs") add
> implementation for FTRACE_WITH_REGS on arm64, we can easily adopt
> the same optimization on arm64.

This is a nice cleanup/refactoring, but I don't think this is an
optimization as such; we're still doing the same work, just in
marginally different place. So I'd suggest s/optimization/cleanup/ here.

It's probably worth noting that this *only* changes the FTRACE_WITH_REGS
implementation, and the mcount-based implementation is unaffected by
this patch.

> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
> ---
> arch/arm64/include/asm/ftrace.h | 7 +++++++
> arch/arm64/kernel/entry-ftrace.S | 6 ------
> arch/arm64/kernel/ftrace.c | 21 +++++++++++++++++++++
> 3 files changed, 28 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
> index 1494cfa8639b..dbc45a4157fa 100644
> --- a/arch/arm64/include/asm/ftrace.h
> +++ b/arch/arm64/include/asm/ftrace.h
> @@ -80,8 +80,15 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
>
> #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> struct dyn_ftrace;
> +struct ftrace_ops;
> +struct ftrace_regs;
> +
> int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
> #define ftrace_init_nop ftrace_init_nop
> +
> +void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
> + struct ftrace_ops *op, struct ftrace_regs *fregs);
> +#define ftrace_graph_func ftrace_graph_func
> #endif
>
> #define ftrace_return_address(n) return_address(n)
> diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S
> index e535480a4069..eb4a69b1f84d 100644
> --- a/arch/arm64/kernel/entry-ftrace.S
> +++ b/arch/arm64/kernel/entry-ftrace.S
> @@ -97,12 +97,6 @@ SYM_CODE_START(ftrace_common)
> SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
> bl ftrace_stub
>
> -#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> -SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller();
> - nop // If enabled, this will be replaced
> - // "b ftrace_graph_caller"
> -#endif
> -

You should also be able to delete the FTRACE_WITH_REGS implementation of
ftrace_graph_caller since that's now unused.

Having that in the diff would also make it easier to compare to the
logic in ftrace_graph_func().

> /*
> * At the callsite x0-x8 and x19-x30 were live. Any C code will have preserved
> * x19-x29 per the AAPCS, and we created frame records upon entry, so we need
> diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
> index 4506c4a90ac1..1b5da231b1de 100644
> --- a/arch/arm64/kernel/ftrace.c
> +++ b/arch/arm64/kernel/ftrace.c
> @@ -268,6 +268,26 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
> }
>
> #ifdef CONFIG_DYNAMIC_FTRACE
> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> +int ftrace_enable_ftrace_graph_caller(void)
> +{
> + return 0;
> +}
> +
> +int ftrace_disable_ftrace_graph_caller(void)
> +{
> + return 0;
> +}

It's a shame the core code doesn't provide this if we provide an
implementation of ftrace_graph_func.

> +
> +void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
> + struct ftrace_ops *op, struct ftrace_regs *fregs)
> +{
> + struct pt_regs *regs = arch_ftrace_get_regs(fregs);
> + unsigned long *parent = (unsigned long *)&procedure_link_pointer(regs);
> +
> + prepare_ftrace_return(ip, parent, frame_pointer(regs));
> +}

Other than my comments above, this looks about right, but I'd like to
give this some testing before I give any tags.

Could you respin this with the FTRACE_WITH_REGS ftrace_graph_caller asm
removed?

Thanks,
Mark.

> +#else
> /*
> * Turn on/off the call to ftrace_graph_caller() in ftrace_caller()
> * depending on @enable.
> @@ -297,5 +317,6 @@ int ftrace_disable_ftrace_graph_caller(void)
> {
> return ftrace_modify_graph_caller(false);
> }
> +#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
> #endif /* CONFIG_DYNAMIC_FTRACE */
> #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
> --
> 2.20.1
>

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