linux-kernel - Re: [PATCH 1/2] perf-probe: Ensure debuginfo's build-id is correct

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Date:   Sat, 6 Jan 2018 23:11:15 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 1/2] perf-probe: Ensure debuginfo's build-id is correct

On Thu, 4 Jan 2018 13:17:28 -0300
Arnaldo Carvalho de Melo <acme@...nel.org> wrote:

> Em Mon, Dec 18, 2017 at 04:29:03PM +0900, Masami Hiramatsu escreveu:
> > Ensure that the build-id of debuginfo is correctly
> > matched to target build-id, if not, it warns user
> > to check the system debuginfo package is correctly
> > installed.
> 
> So we look at a variety of files looking for one that has a matching
> build-id, I think the warning message should state that the file with
> the unmatched build-id is simply being skipped, no?

That is a corner case. In most cases, the debuginfo file will not be
found and silently skipped. We warn only if the debuginfo file exist,
but the version is not matched.

> And why do this at 'perf probe -l' time? I.e. at that point whatever
> probes that are in place already have all the needed debug info?

This is shown not only for perf probe -l, but also other debuginfo
usecases. So, if you installed an old debuginfo but has same filename
with new one, this message will be shown if you try perf probe -a func:line etc. 


> 
> I.e. the warning should be done at probe creation time only?

I think both are good, because if you see this warning, you will
incorrectly install debuginfo files or perf's debuginfo detection
doesn't work correctly on that environment (e.g. new distro).

Thank you, 

> 
> - Arnaldo
>  
> > E.g. on such environment, you will see below warning.
> >   ======
> >   # perf probe -l
> >   WARN: There is a build-id mismatch between
> >    /usr/lib/debug/usr/lib64/libc-2.25.so.debug
> >    and
> >    /usr/lib64/libc-2.25.so
> >   Please check your system's debuginfo files for mismatches, e.g. check
> >   the versions for the target package and debuginfo package.
> >     probe_libc:malloc_get_state (on malloc_get_state@...BC_2.2.5 in /us
> >   r/lib64/libc-2.25.so)
> >   ======
> > 
> > Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> > ---
> >  tools/perf/util/probe-finder.c |   18 ++++++++++++++++++
> >  1 file changed, 18 insertions(+)
> > 
> > diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> > index a5731de0e5eb..5bb71e056b21 100644
> > --- a/tools/perf/util/probe-finder.c
> > +++ b/tools/perf/util/probe-finder.c
> > @@ -119,9 +119,11 @@ enum dso_binary_type distro_dwarf_types[] = {
> >  
> >  struct debuginfo *debuginfo__new(const char *path)
> >  {
> > +	u8 bid[BUILD_ID_SIZE], bid2[BUILD_ID_SIZE];
> >  	enum dso_binary_type *type;
> >  	char buf[PATH_MAX], nil = '\0';
> >  	struct dso *dso;
> > +	bool have_build_id = false;
> >  	struct debuginfo *dinfo = NULL;
> >  
> >  	/* Try to open distro debuginfo files */
> > @@ -129,12 +131,28 @@ struct debuginfo *debuginfo__new(const char *path)
> >  	if (!dso)
> >  		goto out;
> >  
> > +	if (filename__read_build_id(path, bid, BUILD_ID_SIZE) > 0)
> > +		have_build_id = true;
> > +
> >  	for (type = distro_dwarf_types;
> >  	     !dinfo && *type != DSO_BINARY_TYPE__NOT_FOUND;
> >  	     type++) {
> >  		if (dso__read_binary_type_filename(dso, *type, &nil,
> >  						   buf, PATH_MAX) < 0)
> >  			continue;
> > +
> > +		if (have_build_id) {
> > +			/* This can be fail because the file doesn't exist */
> > +			if (filename__read_build_id(buf, bid2,
> > +						    BUILD_ID_SIZE) < 0)
> > +				continue;
> > +			if (memcmp(bid, bid2, BUILD_ID_SIZE)) {
> > +				pr_warning("WARN: There is a build-id mismatch between\n %s\n and\n %s\n"
> > +					"Please check your system's debuginfo files for mismatches, e.g. check the "
> > +					"versions for the target package and debuginfo package.\n", buf, path);
> > +				continue;
> > +			}
> > +		}
> >  		dinfo = __debuginfo__new(buf);
> >  	}
> >  	dso__put(dso);


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