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

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Date:	Tue, 30 Jul 2013 13:37:24 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Adrian Hunter <adrian.hunter@...el.com>
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

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?

Thanks,
Namhyung


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