netdev - Re: [PATCH v9 02/11] fprobe: Add ftrace based probe APIs

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Date:   Mon, 7 Mar 2022 13:55:31 +0100
From:   Jiri Olsa <olsajiri@...il.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH v9 02/11] fprobe: Add ftrace based probe APIs

On Sun, Mar 06, 2022 at 06:36:03PM +0900, Masami Hiramatsu wrote:

SNIP

> +}
> +NOKPROBE_SYMBOL(fprobe_handler);
> +
> +/* Convert ftrace location address from symbols */
> +static unsigned long *get_ftrace_locations(const char **syms, int num)
> +{
> +	unsigned long addr, size;
> +	unsigned long *addrs;
> +	int i;
> +
> +	/* Convert symbols to symbol address */
> +	addrs = kcalloc(num, sizeof(*addrs), GFP_KERNEL);
> +	if (!addrs)
> +		return ERR_PTR(-ENOMEM);
> +
> +	for (i = 0; i < num; i++) {
> +		addrs[i] = kallsyms_lookup_name(syms[i]);
> +		if (!addrs[i])	/* Maybe wrong symbol */
> +			goto error;
> +	}
> +
> +	/* Convert symbol address to ftrace location. */
> +	for (i = 0; i < num; i++) {
> +		if (!kallsyms_lookup_size_offset(addrs[i], &size, NULL) || !size)
> +			goto error;
> +		addr = ftrace_location_range(addrs[i], addrs[i] + size - 1);
> +		if (!addr) /* No dynamic ftrace there. */
> +			goto error;
> +		addrs[i] = addr;
> +	}

why not one just single loop ?

jirka


> +
> +	return addrs;
> +
> +error:
> +	kfree(addrs);
> +
> +	return ERR_PTR(-ENOENT);
> +}
> +
> +static void fprobe_init(struct fprobe *fp)
> +{
> +	fp->nmissed = 0;
> +	fp->ops.func = fprobe_handler;
> +	fp->ops.flags |= FTRACE_OPS_FL_SAVE_REGS;
> +}

SNIP