linux-kernel - Re: [PATCH V4 6/7] riscv: ftrace: Add DYNAMIC_FTRACE_WITH_DIRECT

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Date:   Thu, 1 Dec 2022 20:02:56 +0000
From:   Conor Dooley <conor@...nel.org>
To:     guoren@...nel.org
Cc:     anup@...infault.org, paul.walmsley@...ive.com, palmer@...belt.com,
        conor.dooley@...rochip.com, heiko@...ech.de, rostedt@...dmis.org,
        mhiramat@...nel.org, jolsa@...hat.com, bp@...e.de,
        jpoimboe@...nel.org, suagrfillet@...il.com, andy.chiu@...ive.com,
        mark.rutland@....com, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V4 6/7] riscv: ftrace: Add
 DYNAMIC_FTRACE_WITH_DIRECT_CALLS support

On Mon, Nov 28, 2022 at 10:32:29PM -0500, guoren@...nel.org wrote:
> From: Song Shuai <suagrfillet@...il.com>
> 
> 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>
> Tested-by: Guo Ren <guoren@...nel.org>
> Signed-off-by: Guo Ren <guoren@...nel.org>
> ---
>  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 1d0e5838b11b..2828537abfcd 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

Please sort new entries here in alphabetical order, so move the new
entry up by one line :)

Thanks,
Conor.