linux-kernel - Re: [BUGFIX PATCH] perf probe: Do not depend on dwfl_module

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Date:   Fri, 28 Feb 2020 08:52:38 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Alexandre Ghiti <alex@...ti.fr>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Sasha Levin <sashal@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [BUGFIX PATCH] perf probe: Do not depend on
 dwfl_module_addrsym()

On Thu, 27 Feb 2020 17:20:39 +0100
Alexandre Ghiti <alex@...ti.fr> wrote:

> On 2/27/20 4:42 PM, Masami Hiramatsu wrote:
> > Do not depend on dwfl_module_addrsym() because it can fail
> > on user-space shared libraries.
> > 
> > Actually, same bug was fixed by commit 664fee3dc379 ("perf
> > probe: Do not use dwfl_module_addrsym if dwarf_diename finds
> > symbol name"), but commit 07d369857808 ("perf probe: Fix
> > wrong address verification) reverted to get actual symbol
> > address from symtab.
> > 
> > This fixes it again by getting symbol address from DIE,
> > and only if the DIE has only address range, it uses
> > dwfl_module_addrsym().
> > 
> > Fixes: 07d369857808 ("perf probe: Fix wrong address verification)
> > Reported-by: Alexandre Ghiti <alex@...ti.fr>
> > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> > ---
> >   tools/perf/util/probe-finder.c |   11 ++++++++---
> >   1 file changed, 8 insertions(+), 3 deletions(-)
> > 
> > diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> > index 1c817add6ca4..e4cff49384f4 100644
> > --- a/tools/perf/util/probe-finder.c
> > +++ b/tools/perf/util/probe-finder.c
> > @@ -637,14 +637,19 @@ static int convert_to_trace_point(Dwarf_Die *sp_die, Dwfl_Module *mod,
> >   		return -EINVAL;
> >   	}
> >   
> > -	/* Try to get actual symbol name from symtab */
> > -	symbol = dwfl_module_addrsym(mod, paddr, &sym, NULL);
> > +	if (dwarf_entrypc(sp_die, &eaddr) == 0) {
> > +		/* If the DIE has entrypc, use it. */
> > +		symbol = dwarf_diename(sp_die);
> > +	} else {
> > +		/* Try to get actual symbol name and address from symtab */
> > +		symbol = dwfl_module_addrsym(mod, paddr, &sym, NULL);
> > +		eaddr = sym.st_value;
> > +	}
> >   	if (!symbol) {
> >   		pr_warning("Failed to find symbol at 0x%lx\n",
> >   			   (unsigned long)paddr);
> >   		return -ENOENT;
> >   	}
> > -	eaddr = sym.st_value;
> >   
> >   	tp->offset = (unsigned long)(paddr - eaddr);
> >   	tp->address = (unsigned long)paddr;
> > 
> 
> I have just tested your patch, that fixes the issue, so you can add:
> 
> Tested-by: Alexandre Ghiti <alex@...ti.fr>

Thanks Alexandre,
Arnaldo, could you also pick this for fix?

Thank you,

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