linux-kernel - Re: [PATCH V7 03/15] kprobes: Add symbols for kprobe insn pages

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Message-Id: <20200528093117.181bf843a2f8f2c39fcf9860@kernel.org>
Date:   Thu, 28 May 2020 09:31:17 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Leo Yan <leo.yan@...aro.org>, Jiri Olsa <jolsa@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V7 03/15] kprobes: Add symbols for kprobe insn pages

On Wed, 27 May 2020 19:43:45 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Tue, May 12, 2020 at 03:19:10PM +0300, Adrian Hunter wrote:
> > @@ -2179,6 +2181,49 @@ int kprobe_add_area_blacklist(unsigned long start, unsigned long end)
> >  	return 0;
> >  }
> >  
> > +int kprobe_cache_get_kallsym(struct kprobe_insn_cache *c, unsigned int *symnum,
> > +			     unsigned long *value, char *type, char *sym)
> > +{
> > +	struct kprobe_insn_page *kip;
> > +	int ret = -ERANGE;
> > +
> > +	rcu_read_lock();
> > +	list_for_each_entry_rcu(kip, &c->pages, list) {
> > +		if ((*symnum)--)
> > +			continue;
> > +		strlcpy(sym, c->sym, KSYM_NAME_LEN);
> > +		*type = 't';
> > +		*value = (unsigned long)kip->insns;
> > +		ret = 0;
> > +		break;
> > +	}
> > +	rcu_read_unlock();
> > +
> > +	return ret;
> > +}
> 
> This fails on sparc64-defconfig.
> 
> In file included from ../include/linux/kprobes.h:19:0,
>                  from ../kernel/kprobes.c:21:
> ../kernel/kprobes.c: In function 'kprobe_cache_get_kallsym':
> ../include/linux/rculist.h:382:49: error: dereferencing pointer to incomplete type 'struct kprobe_insn_page'
> 
> Please provide a new patch.

Ah, yes. Since some archs doesn't require special out-of-line
trampoline, we need to check __ARCH_WANT_KPROBES_INSN_SLOT,
and if not, kprobe_cache_get_kallsym() has do nothing and 
return -ERANGE.

Thank you,


-- 
Masami Hiramatsu <mhiramat@...nel.org>