Re: [PATCH 1/2] riscv/ftrace: add DYNAMIC_FTRACE_WITH_DIRECT_CALLS support

From: Guo Ren
Date: Mon Nov 28 2022 - 08:19:55 EST


On Wed, Nov 23, 2022 at 10:20 PM Song Shuai <suagrfillet@xxxxxxxxx> 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@xxxxxxxxx>
> ---
> 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