linux-kernel - Re: [PATCH 1/2] riscv/ftrace: add DYNAMIC_FTRACE_WITH_DIRECT

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Date:   Mon, 28 Nov 2022 21:16:57 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Song Shuai <suagrfillet@...il.com>
Cc:     paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, rostedt@...dmis.org, mhiramat@...nel.org,
        mark.rutland@....com, peterz@...radead.org, jolsa@...hat.com,
        bp@...e.de, jpoimboe@...nel.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] riscv/ftrace: add DYNAMIC_FTRACE_WITH_DIRECT_CALLS support

On Wed, Nov 23, 2022 at 10:20 PM Song Shuai <suagrfillet@...il.com> wrote:
>
> This patch adds DYNAMIC_FTRACE_WITH_DIRECT_CALLS support for RISC-V.
>
> select the DYNAMIC_FTRACE_WITH_DIRECT_CALLS to provide the
> register_ftrace_direct[_multi] interfaces allowing users to register
> the customed trampoline (direct_caller) as the mcount for one or
> more target functions. And modify_ftrace_direct[_multi] are also
> provided for modifying direct_caller.
>
> To make the direct_caller and the other ftrace hooks (eg. function/fgraph
> tracer, k[ret]probes) co-exist, a temporary register is nominated to
> store the address of direct_caller in ftrace_regs_caller. After the
> setting of the address direct_caller by direct_ops->func and the
> RESTORE_REGS in ftrace_regs_caller, direct_caller will be jumped to
> by the `jr` inst.
>
> Signed-off-by: Song Shuai <suagrfillet@...il.com>
> ---
>  arch/riscv/Kconfig              | 1 +
>  arch/riscv/include/asm/ftrace.h | 6 ++++++
>  arch/riscv/kernel/mcount-dyn.S  | 4 ++++
>  3 files changed, 11 insertions(+)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 39ec8d628cf6..d083ec08d0b6 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -278,6 +278,7 @@ config ARCH_RV64I
>         select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
>         select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && $(cc-option,-fpatchable-function-entry=8)
>         select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
> +       select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
>         select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
>         select HAVE_FUNCTION_GRAPH_TRACER
>         select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !PREEMPTION
> diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
> index 01bebb28eabe..be4d57566139 100644
> --- a/arch/riscv/include/asm/ftrace.h
> +++ b/arch/riscv/include/asm/ftrace.h
> @@ -114,6 +114,12 @@ struct ftrace_regs;
>  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
> +
> +static inline void arch_ftrace_set_direct_caller(struct pt_regs *regs, unsigned long addr)
> +{
> +               regs->t1 = addr;
> +}
> +
>  #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
>
>  #endif /* __ASSEMBLY__ */
> diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
> index 466c6ef217b1..b89c85a58569 100644
> --- a/arch/riscv/kernel/mcount-dyn.S
> +++ b/arch/riscv/kernel/mcount-dyn.S
> @@ -233,6 +233,7 @@ ENDPROC(ftrace_caller)
>  #else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
>  ENTRY(ftrace_regs_caller)
>         SAVE_ABI_REGS 1
> +       REG_S   x0, PT_T1(sp)
ENTRY(ftrace_regs_caller)
+    move t1, zero
      SAVE_ABI_REGS 1
      PREPARE_ARGS

Shall we use a move here, instead?

>         PREPARE_ARGS
>
>  ftrace_regs_call:
> @@ -241,7 +242,10 @@ ftrace_regs_call:
>
>
>         RESTORE_ABI_REGS 1
> +       bnez    t1,.Ldirect
>         jr t0
> +.Ldirect:
> +       jr t1
>  ENDPROC(ftrace_regs_caller)
>
>  ENTRY(ftrace_caller)
> --
> 2.20.1
>


-- 
Best Regards
 Guo Ren