linux-kernel - Re: [PATCHv2] perf probe: Fix failure to add multiple probes without debuginfo

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Date:	Fri, 20 Mar 2015 10:50:50 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	He Kuang <hekuang@...wei.com>, a.p.zijlstra@...llo.nl,
	mingo@...hat.com, namhyung@...nel.org, wangnan0@...wei.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2] perf probe: Fix failure to add multiple probes without
 debuginfo

Em Fri, Mar 20, 2015 at 04:42:46PM +0900, Masami Hiramatsu escreveu:
> (2015/03/20 10:56), He Kuang wrote:
> > Perf tries to find probe function addresses from map when debuginfo
> > could not be found.
> > 
> > To the first added function, the value of ref_reloc_sym was set in
> > maps__set_kallsyms_ref_reloc_sym() and can be obtained from
> > host_machine->kmaps->maps. After that, new maps are added to
> > host_machine->kmaps->maps in dso__load_kcore(), all these new added maps
> > do not have a valid ref_reloc_sym.
> > 
> > When adding a second function, get_target_map() may get a map without
> > valid ref_reloc_sym, and raise the error "Relocated base symbol is not
> > found".
> > 
> > Fix this by using kernel_get_ref_reloc_sym() to get ref_reloc_sym.
> > 
> > This problem can be reproduced as following:
> > 
> >   $ perf probe --add='sys_write' --add='sys_open'
> >   Relocated base symbol is not found!
> >     Error: Failed to add events.
> > 
> > After this patch:
> > 
> >   $ perf probe --add='sys_write' --add='sys_open'
> >   Added new event:
> >     probe:sys_write      (on sys_write)
> > 
> >   You can now use it in all perf tools, such as:
> > 
> >       perf record -e probe:sys_write -aR sleep 1
> > 
> >   Added new event:
> >     probe:sys_open       (on sys_open)
> > 
> >   You can now use it in all perf tools, such as:
> > 
> >       perf record -e probe:sys_open -aR sleep 1
> > 
> 
> OK, I've checked that this solve the problem :)
> 
> Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

Ok, next time, please consider sending a Tested-by: tag instead, if what
you did was to apply the patch, check that it fixes the problem, that
provides a stronger patch endorsement.

- Arnaldo
 
> 
> Thank you!
> 
> > Signed-off-by: He Kuang <hekuang@...wei.com>
> > ---
> >  tools/perf/util/probe-event.c | 4 +---
> >  1 file changed, 1 insertion(+), 3 deletions(-)
> > 
> > diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> > index c5e1338..c1ccd6a 100644
> > --- a/tools/perf/util/probe-event.c
> > +++ b/tools/perf/util/probe-event.c
> > @@ -2507,7 +2507,6 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
> >  					    int max_tevs, const char *target)
> >  {
> >  	struct map *map = NULL;
> > -	struct kmap *kmap = NULL;
> >  	struct ref_reloc_sym *reloc_sym = NULL;
> >  	struct symbol *sym;
> >  	struct probe_trace_event *tev;
> > @@ -2540,8 +2539,7 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
> >  	}
> >  
> >  	if (!pev->uprobes && !pp->retprobe) {
> > -		kmap = map__kmap(map);
> > -		reloc_sym = kmap->ref_reloc_sym;
> > +		reloc_sym = kernel_get_ref_reloc_sym();
> >  		if (!reloc_sym) {
> >  			pr_warning("Relocated base symbol is not found!\n");
> >  			ret = -EINVAL;
> > 
> 
> 
> -- 
> Masami HIRAMATSU
> Software Platform Research Dept. Linux Technology Research Center
> Hitachi, Ltd., Yokohama Research Laboratory
> E-mail: masami.hiramatsu.pt@...achi.com
> 
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