linux-kernel - Re: [PATCH perf/core v4 03/19] perf buildid-cache: Fall back to the old style build-id cache

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Message-ID: <20160426134749.GB20998@kernel.org>
Date:	Tue, 26 Apr 2016 10:47:49 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Masami Hiramatsu <mhiramat@...nel.org>
Cc:	linux-kernel@...r.kernel.org, Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Hemant Kumar <hemant@...ux.vnet.ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>
Subject: Re: [PATCH perf/core v4 03/19] perf buildid-cache: Fall back to the
 old style build-id cache

Em Tue, Apr 26, 2016 at 06:02:33PM +0900, Masami Hiramatsu escreveu:
> Fall back to the old style build-id cache
> (~/.debug/<path-to-bin>/<build-id>) if possible.
> Because there is old build-id cache under ~/.debug, perf
> has to check if the old entry is there instead of returning
> an error. Or, user have to remove ~/.debug completely.

So, from the description this seems to address the issues I mentioned in
the previous patch.

Probably it is a good idea not to introduce the problem in the first
place? I.e. combine this and the previous patch, so that we don't have
this bisection break?

- Arnaldo
 
> This patch introduces fallback code to try using old-style
> buildid caches. To update the cached entry, you just need to
> add a cache. It automatically removes old cache entry and
> make a new one in new style
> (~/.debug/<path-to-bin>/<build-id>/[elf|vdso|kallsyms]).
> 
> IOW, without this patch, "perf buildid-cache --add" always
> gets errors when adding existing binaries.
>   ----
>   # perf buildid-cache -a /usr/lib64/libc-2.20.so,/usr/bin/gcc
>   Couldn't add /usr/bin/gcc: Not a directory
>   Couldn't add /usr/lib64/libc-2.20.so: Not a directory
>   ----
> Moreover, --update option removes only symlink, thus the
> build-id cache is corrupted.
> 
> This fixes above issues.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  tools/perf/util/build-id.c |   17 ++++++++++++++++-
>  tools/perf/util/symbol.c   |   13 +++++++++----
>  2 files changed, 25 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/perf/util/build-id.c b/tools/perf/util/build-id.c
> index 46a8bcc..b035483 100644
> --- a/tools/perf/util/build-id.c
> +++ b/tools/perf/util/build-id.c
> @@ -155,6 +155,12 @@ static char *build_id_cache__linkname(const char *sbuild_id, char *bf,
>  	return bf;
>  }
>  
> +static bool __is_regular_file(const char *pathname)
> +{
> +	struct stat sb;
> +	return stat(pathname, &sb) == 0 && S_ISREG(sb.st_mode);
> +}
> +
>  static const char *build_id_cache__basename(bool is_kallsyms, bool is_vdso)
>  {
>  	return is_kallsyms ? "kallsyms" : (is_vdso ? "vdso" : "elf");
> @@ -177,7 +183,11 @@ char *dso__build_id_filename(const struct dso *dso, char *bf, size_t size)
>  	if (!linkname)
>  		return NULL;
>  
> -	ret = asnprintf(&bf, size, "%s/%s", linkname,
> +	/* Check if old style build_id cache */
> +	if (__is_regular_file(linkname))
> +		ret = asnprintf(&bf, size, "%s", linkname);
> +	else
> +		ret = asnprintf(&bf, size, "%s/%s", linkname,
>  			 build_id_cache__basename(is_kallsyms, is_vdso));
>  	if (ret < 0 || (!alloc && size < (unsigned int)ret))
>  		bf = NULL;
> @@ -445,6 +455,11 @@ int build_id_cache__add_s(const char *sbuild_id, const char *name,
>  	if (!dir_name)
>  		goto out_free;
>  
> +	/* Remove old style build-id cache */
> +	if (__is_regular_file(dir_name))
> +		if (unlink(dir_name))
> +			goto out_free;
> +
>  	if (mkdir_p(dir_name, 0755))
>  		goto out_free;
>  
> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
> index c57cb47..9463c7d 100644
> --- a/tools/perf/util/symbol.c
> +++ b/tools/perf/util/symbol.c
> @@ -1687,11 +1687,16 @@ static char *dso__find_kallsyms(struct dso *dso, struct map *map)
>  
>  	scnprintf(path, sizeof(path), "%s/[kernel.kallsyms]/%s/kallsyms",
>  		  buildid_dir, sbuild_id);
> -
> +	/* Try old style kallsyms cache */
>  	if (access(path, F_OK)) {
> -		pr_err("No kallsyms or vmlinux with build-id %s was found\n",
> -		       sbuild_id);
> -		return NULL;
> +		scnprintf(path, sizeof(path), "%s/[kernel.kallsyms]/%s",
> +			  buildid_dir, sbuild_id);
> +
> +		if (access(path, F_OK)) {
> +			pr_err("No kallsyms or vmlinux with build-id %s was found\n",
> +			       sbuild_id);
> +			return NULL;
> +		}
>  	}
>  
>  	return strdup(path);