linux-kernel - Re: [PATCH v5] perf machine: arm/arm64: Improve completeness for kernel address space

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Message-ID: <20190904085912.GA27922@leoy-ThinkPad-X240s>
Date:   Wed, 4 Sep 2019 16:59:12 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, clang-built-linux@...glegroups.com,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Suzuki Poulouse <suzuki.poulose@....com>,
        coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5] perf machine: arm/arm64: Improve completeness for
 kernel address space

Hi Adrian,

On Wed, Sep 04, 2019 at 10:26:13AM +0300, Adrian Hunter wrote:

[...]

> > Could you take chance to review my below replying?  I'd like to get
> > your confirmation before I send out offical patch.
> 
> It is not necessary to do kallsyms__parse for x86_64, so it would be better
> to check the arch before calling that.

Thanks for suggestion, will do it in the formal patch.

> However in general, having to copy and use kallsyms with perf.data if on a
> different arch does not seem very user friendly.

Agree.  Seems it's more reasonable to save related info in
perf.data; TBH, I have no idea for how to do that.

> But really that is up to Arnaldo.

@Arnaldo, if possible could you take a look for below change?

If you don't think below code is the right thing and it's not a common
issue, then maybe it's more feasible to resolve this issue only for
Arm CoreSight specific.

Please let me know how about you think for this?

Thanks,
Leo Yan

> >> For your question for taking a perf.data file to a machine with a
> >> different architecture, we can firstly use command 'perf buildid-list'
> >> to print out the buildid for kallsyms, based on the dumped buildid we
> >> can find out the location for the saved kallsyms file; then we can use
> >> option '--kallsyms' to specify the offline kallsyms file and use the
> >> offline kallsyms to fixup kernel start address.  The detailed commands
> >> are listed as below:
> >>
> >> root@...ian:~# perf buildid-list
> >> 7b36dfca8317ef74974ebd7ee5ec0a8b35c97640 [kernel.kallsyms]
> >> 56b84aa88a1bcfe222a97a53698b92723a3977ca /usr/lib/systemd/systemd
> >> 0956b952e9cd673d48ff2cfeb1a9dbd0c853e686 /usr/lib/aarch64-linux-gnu/libm-2.28.so
> >> [...]
> >>
> >> root@...ian:~# perf script --kallsyms ~/.debug/\[kernel.kallsyms\]/7b36dfca8317ef74974ebd7ee5ec0a8b35c97640/kallsyms
> >>
> >> The amended patch is as below, please review and always welcome
> >> any suggestions or comments!
> >>
> >> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> >> index 5734460fc89e..593f05cc453f 100644
> >> --- a/tools/perf/util/machine.c
> >> +++ b/tools/perf/util/machine.c
> >> @@ -2672,9 +2672,26 @@ int machine__nr_cpus_avail(struct machine *machine)
> >>  	return machine ? perf_env__nr_cpus_avail(machine->env) : 0;
> >>  }
> >>  
> >> +static int machine__fixup_kernel_start(void *arg,
> >> +				       const char *name __maybe_unused,
> >> +				       char type,
> >> +				       u64 start)
> >> +{
> >> +	struct machine *machine = arg;
> >> +
> >> +	type = toupper(type);
> >> +
> >> +	/* Fixup for text, weak, data and bss sections. */
> >> +	if (type == 'T' || type == 'W' || type == 'D' || type == 'B')
> >> +		machine->kernel_start = min(machine->kernel_start, start);
> >> +
> >> +	return 0;
> >> +}
> >> +
> >>  int machine__get_kernel_start(struct machine *machine)
> >>  {
> >>  	struct map *map = machine__kernel_map(machine);
> >> +	char filename[PATH_MAX];
> >>  	int err = 0;
> >>  
> >>  	/*
> >> @@ -2696,6 +2713,22 @@ int machine__get_kernel_start(struct machine *machine)
> >>  		if (!err && !machine__is(machine, "x86_64"))
> >>  			machine->kernel_start = map->start;
> >>  	}
> >> +
> >> +	if (symbol_conf.kallsyms_name != NULL) {
> >> +		strncpy(filename, symbol_conf.kallsyms_name, PATH_MAX);
> >> +	} else {
> >> +		machine__get_kallsyms_filename(machine, filename, PATH_MAX);
> >> +
> >> +		if (symbol__restricted_filename(filename, "/proc/kallsyms"))
> >> +			goto out;
> >> +	}
> >> +
> >> +	if (kallsyms__parse(filename, machine, machine__fixup_kernel_start))
> >> +		pr_warning("Fail to fixup kernel start address. skipping...\n");
> >> +
> >> +out:
> >>  	return err;
> >>  }
> >>  
> >>
> >> Thanks,
> >> Leo Yan
> > 
>