linux-kernel - Re: [PATCH 7/9] perf tools: add support for reading from /proc/kcore

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Date:	Wed, 31 Jul 2013 00:12:15 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Namhyung Kim <namhyung@...nel.org>
CC:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel@...r.kernel.org, David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 7/9] perf tools: add support for reading from /proc/kcore

On 30/07/2013 7:37 a.m., Namhyung Kim wrote:
> Hi,
>
> On Thu, 25 Jul 2013 17:01:28 +0300, Adrian Hunter wrote:
>> In the absence of vmlinux, perf tools uses kallsyms
>> for symbols.  If the user has access, now also map to
>> /proc/kcore.
>>
>> The dso data_type is now set to either
>> DSO_BINARY_TYPE__KCORE or DSO_BINARY_TYPE__GUEST_KCORE
>> as approprite.
>
> [SNIP]
>> +
>> +static bool is_host_buildid_str(const char *str)
>> +{
>> +	u8 host_build_id[BUILD_ID_SIZE];
>> +	char host_build_id_str[BUILD_ID_SIZE * 2 + 1];
>> +
>> +	if (sysfs__read_build_id("/sys/kernel/notes", host_build_id,
>> +				 sizeof(host_build_id)))
>> +		return false;
>> +
>> +	build_id__sprintf(host_build_id, sizeof(host_build_id),
>> +			  host_build_id_str);
>> +
>> +	return !strcmp(str, host_build_id_str);
>> +}
>> +
>> +/*
>> + * If kallsyms is referenced by name then we look for kcore in the same
>> + * directory.  Otherwise we use /proc/kcore but only if the buildid matches the
>> + * host.
>> + */
>> +static bool kcore_filename_from_kallsyms_filename(char *kcore_filename,
>> +						  const char *kallsyms_filename)
>> +{
>> +	char *name;
>> +
>> +	strcpy(kcore_filename, kallsyms_filename);
>> +	name = strrchr(kcore_filename, '/');
>> +	if (!name)
>> +		return false;
>> +
>> +	if (!strcmp(name, "/kallsyms")) {
>> +		strcpy(name, "/kcore");
>> +		return true;
>> +	}
>> +
>> +	if (is_host_buildid_str(name)) {
>
> IIUC the name should start with '/' but build-id is not.  So doesn't it
> always fail?

In fact I realized the whole thing is not necessary. Fixed in V2.

>
> Thanks,
> Namhyung
>
>
>> +		strcpy(kcore_filename, "/proc/kcore");
>> +		return true;
>> +	}
>> +
>> +	return false;
>> +}

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