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

Guo Ren
2022-11-28T12:55:06Z

Abandoned

On Mon, Nov 28, 2022 at 6:12 PM <guoren@kernel.org> wrote:
>
> From: Song Shuai <suagrfillet@gmail.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@gmail.com>
> Co-developed-by: Guo Ren <guoren@kernel.org>
> Signed-off-by: Guo Ren <guoren@kernel.org>
> ---
> Remove modification of mcount-dyn.S. (Guo Ren)
> ---
> arch/riscv/Kconfig | 1 +
> arch/riscv/include/asm/ftrace.h | 26 ++++++++++++++++++++++++++
> 2 files changed, 27 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
> diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
> index 84f856a3286e..d2c159cdfa5c 100644
> --- a/arch/riscv/include/asm/ftrace.h
> +++ b/arch/riscv/include/asm/ftrace.h
> @@ -114,6 +114,32 @@ 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)
> +{
> + /*
> + * Backup origin detour target (t0) in t1, and set t0 with addr.
> + *
> + * Here is the sample code for riscv direct_caller:
> + *
> + * addi sp,sp,-16
> + * move t0,t1
> + * ^^^^^^^^^^
> + * sd t0,0(sp)
> + * sd ra,8(sp)
> + * call my_direct_func1
> + * ld t0,0(sp)
> + * ld ra,8(sp)
> + * addi sp,sp,16
> + * jr t0
> + *
> + * (Set t0 with t1 for continuous detour, because t1 contains origin detour
> + * target)
> + */
> + regs->t1 = regs->t0;
> + regs->t0 = addr;
> +}
> +
> #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
>
> #endif /* __ASSEMBLY__ */
> --
> 2.36.1