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Date:   Tue, 06 Jul 2021 12:10:36 -0700 (PDT)
Subject:     Re: [PATCH] riscv: ptrace: add argn syntax
In-Reply-To: <20210620120151.17860-1-huan.xie@suse.com>
CC:     oleg@redhat.com, Paul Walmsley <paul.walmsley@sifive.com>,
        caou@eecs.berkeley.edu, linux-riscv@lists.infradead.org,
        linux-kernel@vger.kernel.org, chongguiguzi@gmail.com,
        huan.xie@suse.com
From:   Palmer Dabbelt <palmer@dabbelt.com>
To:     chongguiguzi@gmail.com
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On Sun, 20 Jun 2021 05:01:51 PDT (-0700), chongguiguzi@gmail.com wrote:
> This enables ftrace kprobe events to access kernel function
> arguments via $argN syntax.
>
> Signed-off-by: Jeff Xie <huan.xie@suse.com>
> ---
>  arch/riscv/Kconfig              |  1 +
>  arch/riscv/include/asm/ptrace.h | 31 +++++++++++++++++++++++++++++++
>  2 files changed, 32 insertions(+)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 18ec0f9bb8d5..f9246a7d0a31 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -88,6 +88,7 @@ config RISCV
>  	select HAVE_PERF_REGS
>  	select HAVE_PERF_USER_STACK_DUMP
>  	select HAVE_REGS_AND_STACK_ACCESS_API
> +	select HAVE_FUNCTION_ARG_ACCESS_API
>  	select HAVE_STACKPROTECTOR
>  	select HAVE_SYSCALL_TRACEPOINTS
>  	select IRQ_DOMAIN
> diff --git a/arch/riscv/include/asm/ptrace.h b/arch/riscv/include/asm/ptrace.h
> index 09ad4e923510..fdb59ee405ee 100644
> --- a/arch/riscv/include/asm/ptrace.h
> +++ b/arch/riscv/include/asm/ptrace.h
> @@ -141,6 +141,37 @@ static inline unsigned long regs_get_register(struct pt_regs *regs,
>
>  	return *(unsigned long *)((unsigned long)regs + offset);
>  }
> +
> +/**
> + * regs_get_kernel_argument() - get Nth function argument in kernel
> + * @regs:       pt_regs of that context
> + * @n:          function argument number (start from 0)
> + *
> + * regs_get_argument() returns @n th argument of the function call.
> + *
> + * Note you can get the parameter correctly if the function has no
> + * more than eight arguments.
> + */
> +static inline unsigned long regs_get_kernel_argument(struct pt_regs *regs,
> +						unsigned int n)
> +{
> +#define NR_REG_ARGUMENTS 8
> +	static const unsigned int argument_offs[] = {
> +		offsetof(struct pt_regs, a0),
> +		offsetof(struct pt_regs, a1),
> +		offsetof(struct pt_regs, a2),
> +		offsetof(struct pt_regs, a3),
> +		offsetof(struct pt_regs, a4),
> +		offsetof(struct pt_regs, a5),
> +		offsetof(struct pt_regs, a6),
> +		offsetof(struct pt_regs, a7),
> +	};
> +
> +	if (n < NR_REG_ARGUMENTS)
> +		return regs_get_register(regs, argument_offs[n]);
> +	return 0;
> +}
> +
>  #endif /* __ASSEMBLY__ */
>
>  #endif /* _ASM_RISCV_PTRACE_H */

This is on for-next.  I cleaned it up a bit to avoid leaking that 
#define.