linux-kernel - Re: [RFC bpf-next 1/4] kallsyms: Add kallsyms_lookup

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Message-ID: <YlZ7bAY1lDQWxUgH@krava>
Date:   Wed, 13 Apr 2022 09:27:40 +0200
From:   Jiri Olsa <olsajiri@...il.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Jiri Olsa <jolsa@...nel.org>, 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>
Subject: Re: [RFC bpf-next 1/4] kallsyms: Add kallsyms_lookup_names function

On Fri, Apr 08, 2022 at 09:57:01AM +0900, Masami Hiramatsu wrote:

SNIP

> >  /*
> >   * These will be re-linked against their real values
> > @@ -572,6 +574,52 @@ int sprint_backtrace_build_id(char *buffer, unsigned long address)
> >  	return __sprint_symbol(buffer, address, -1, 1, 1);
> >  }
> >  
> > +static int symbols_cmp(const void *a, const void *b)
> > +{
> > +	const char **str_a = (const char **) a;
> > +	const char **str_b = (const char **) b;
> > +
> > +	return strcmp(*str_a, *str_b);
> > +}
> > +
> > +struct kallsyms_data {
> > +	unsigned long *addrs;
> > +	const char **syms;
> > +	u32 cnt;
> > +	u32 found;
> 
> BTW, why do you use 'u32' for this arch independent code?
> I think 'size_t' will make its role clearer.

right, will change

> 
> > +};
> > +
> > +static int kallsyms_callback(void *data, const char *name,
> > +			     struct module *mod, unsigned long addr)
> > +{
> > +	struct kallsyms_data *args = data;
> > +
> > +	if (!bsearch(&name, args->syms, args->cnt, sizeof(*args->syms), symbols_cmp))
> > +		return 0;
> > +
> > +	addr = ftrace_location(addr);
> > +	if (!addr)
> > +		return 0;
> > +
> > +	args->addrs[args->found++] = addr;
> > +	return args->found == args->cnt ? 1 : 0;
> > +}
> > +
> > +int kallsyms_lookup_names(const char **syms, u32 cnt, unsigned long *addrs)
> 
> Ditto. I think 'size_t cnt' is better. 

ok, thanks

jirka

> 
> Thank you,
> 
> > +{
> > +	struct kallsyms_data args;
> > +
> > +	sort(syms, cnt, sizeof(*syms), symbols_cmp, NULL);
> > +
> > +	args.addrs = addrs;
> > +	args.syms = syms;
> > +	args.cnt = cnt;
> > +	args.found = 0;
> > +	kallsyms_on_each_symbol(kallsyms_callback, &args);
> > +
> > +	return args.found == args.cnt ? 0 : -EINVAL;
> > +}
> > +
> >  /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
> >  struct kallsym_iter {
> >  	loff_t pos;
> > -- 
> > 2.35.1
> > 
> 
> 
> -- 
> Masami Hiramatsu <mhiramat@...nel.org>