linux-kernel - Re: [PATCH V2 9/9] perf buildid-cache: Check relocation when checking for existing kcore

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Date:	Wed, 29 Jan 2014 16:14:54 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH V2 9/9] perf buildid-cache: Check relocation when
 checking for existing kcore

Em Wed, Jan 29, 2014 at 04:14:44PM +0200, Adrian Hunter escreveu:
> perf buildid-cache does not make another
> copy of kcore if the buildid and modules
> match an existing copy.  That does not

Humm, what is the problem? Having the ref reloc symbol we can fix things
up, no? I.e. just using map->reloc the old kcore copy should be ok to
use, no need to replace the kcore copy in the cache. Or am I missing
something?

- Arnaldo

> take into account the possibility that
> the kernel has been relocated.  Extend
> the check to check if the reference
> relocation symbol matches too, otherwise
> do make a copy.
> 
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> ---
>  tools/perf/builtin-buildid-cache.c | 33 +++++++++++++++++++++++++++++----
>  1 file changed, 29 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/builtin-buildid-cache.c b/tools/perf/builtin-buildid-cache.c
> index cfede86..b22dbb1 100644
> --- a/tools/perf/builtin-buildid-cache.c
> +++ b/tools/perf/builtin-buildid-cache.c
> @@ -63,11 +63,35 @@ static int build_id_cache__kcore_dir(char *dir, size_t sz)
>  	return 0;
>  }
>  
> +static bool same_kallsyms_reloc(const char *from_dir, char *to_dir)
> +{
> +	char from[PATH_MAX];
> +	char to[PATH_MAX];
> +	const char *name;
> +	u64 addr1 = 0, addr2 = 0;
> +	int i;
> +
> +	scnprintf(from, sizeof(from), "%s/kallsyms", from_dir);
> +	scnprintf(to, sizeof(to), "%s/kallsyms", to_dir);
> +
> +	for (i = 0; (name = ref_reloc_sym_names[i]) != NULL; i++) {
> +		addr1 = kallsyms__get_function_start(from, name);
> +		if (addr1)
> +			break;
> +	}
> +
> +	if (name)
> +		addr2 = kallsyms__get_function_start(to, name);
> +
> +	return addr1 == addr2;
> +}
> +
>  static int build_id_cache__kcore_existing(const char *from_dir, char *to_dir,
>  					  size_t to_dir_sz)
>  {
>  	char from[PATH_MAX];
>  	char to[PATH_MAX];
> +	char to_subdir[PATH_MAX];
>  	struct dirent *dent;
>  	int ret = -1;
>  	DIR *d;
> @@ -86,10 +110,11 @@ static int build_id_cache__kcore_existing(const char *from_dir, char *to_dir,
>  			continue;
>  		scnprintf(to, sizeof(to), "%s/%s/modules", to_dir,
>  			  dent->d_name);
> -		if (!compare_proc_modules(from, to)) {
> -			scnprintf(to, sizeof(to), "%s/%s", to_dir,
> -				  dent->d_name);
> -			strlcpy(to_dir, to, to_dir_sz);
> +		scnprintf(to_subdir, sizeof(to_subdir), "%s/%s",
> +			  to_dir, dent->d_name);
> +		if (!compare_proc_modules(from, to) &&
> +		    same_kallsyms_reloc(from_dir, to_subdir)) {
> +			strlcpy(to_dir, to_subdir, to_dir_sz);
>  			ret = 0;
>  			break;
>  		}
> -- 
> 1.7.11.7
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