linux-kernel - Re: [PATCH v5 6/9] riscv/kprobe: Add code to check if kprobe can be optimized

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Message-ID: <87sfgsvmnj.fsf@all.your.base.are.belong.to.us>
Date:   Mon, 02 Jan 2023 19:04:00 +0100
From:   Björn Töpel <bjorn@...nel.org>
To:     Chen Guokai <chenguokai17@...ls.ucas.ac.cn>,
        paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, rostedt@...dmis.org, mingo@...hat.com,
        sfr@...b.auug.org.au
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        liaochang1@...wei.com, Chen Guokai <chenguokai17@...ls.ucas.ac.cn>
Subject: Re: [PATCH v5 6/9] riscv/kprobe: Add code to check if kprobe can be
 optimized

Chen Guokai <chenguokai17@...ls.ucas.ac.cn> writes:

> From: Liao Chang <liaochang1@...wei.com>

> diff --git a/arch/riscv/kernel/probes/opt.c b/arch/riscv/kernel/probes/opt.c
> index a0d2ab39e3fa..258a283c906d 100644
> --- a/arch/riscv/kernel/probes/opt.c
> +++ b/arch/riscv/kernel/probes/opt.c
> @@ -271,15 +271,103 @@ static void find_free_registers(struct kprobe *kp, struct optimized_kprobe *op,
>  	*ra = (kw == 1UL) ? 0 : __builtin_ctzl(kw & ~1UL);
>  }
>  
> +static bool insn_jump_into_range(unsigned long addr, unsigned long start,
> +				 unsigned long end)
> +{
> +	kprobe_opcode_t insn = *(kprobe_opcode_t *)addr;
> +	unsigned long target, offset = GET_INSN_LENGTH(insn);
> +
> +#ifdef CONFIG_RISCV_ISA_C
> +	if (offset == RVC_INSN_LEN) {
> +		if (riscv_insn_is_c_beqz(insn) || riscv_insn_is_c_bnez(insn))
> +			target = addr + rvc_branch_imme(insn);
> +		else if (riscv_insn_is_c_jal(insn) || riscv_insn_is_c_j(insn))
> +			target = addr + rvc_jal_imme(insn);
> +		else
> +			target = 0;
> +		return (target >= start) && (target < end);
> +	}
> +#endif
> +
> +	if (riscv_insn_is_branch(insn))
> +		target = addr + rvi_branch_imme(insn);
> +	else if (riscv_insn_is_jal(insn))
> +		target = addr + rvi_jal_imme(insn);
> +	else
> +		target = 0;
> +	return (target >= start) && (target < end);
> +}
> +
> +static int search_copied_insn(unsigned long paddr, struct optimized_kprobe *op)
> +{
> +	int i =  1;
> +	unsigned long offset = GET_INSN_LENGTH(*(kprobe_opcode_t *)paddr);
> +
> +	while ((i++ < MAX_COPIED_INSN) && (offset < 2 * RVI_INSN_LEN)) {
> +		if (riscv_probe_decode_insn((probe_opcode_t *)paddr + offset,
> +					    NULL) != INSN_GOOD)

If the second argument is NULL, and the insn is auipc, we'll splat with
NULL-ptr exception.

Hmm, probe_opcode_t is u32, right? And GET_INSN_LENGTH() returns 4 or 2
...then the pointer arithmetic will be a mess?


Björn