linux-kernel - Re: [PATCH v2 2/3] perf-probe: Ignore vmlinux buildid if offline kernel is given

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Message-Id: <20160826230238.429b06d779f9c1c34f78bab2@kernel.org>
Date:   Fri, 26 Aug 2016 23:02:38 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH v2 2/3] perf-probe: Ignore vmlinux buildid if offline
 kernel is given

On Fri, 26 Aug 2016 01:24:42 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> Ignore the buildid of running kernel when both of --definition and
> --vmlinux is given because that kernel should be off-line.
> This also skips post-processing of kprobe event for relocating
> symbol and checking blacklist, because it can not be done on
> off-line kernel.

Ahh, I missed other commands which doesn't change running kernel,
like --funcs, --vars, --lines. Those also should ignore buildid if
vmlinux is given. (--add, --del, and --list depend on/change running
kernel)

I'll add a patch to handle that.

Thank you,

> 
> E.g. without this fix perf shows an error as below
>   ----
>   $ perf probe --vmlinux=./vmlinux-arm --definition do_sys_open
>   ./vmlinux-arm with build id 7a1f76dd56e9c4da707cd3d6333f50748141434b not found, continuing without symbols
>   Failed to find symbol do_sys_open in kernel
>     Error: Failed to add events.
>   ----
> with this fix, we can get the definition
>   ----
>   $ perf probe --vmlinux=./vmlinux-arm --definition do_sys_open
>   p:probe/do_sys_open do_sys_open+0
>   ----
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  Changes from v1:
>   - Update the condition since --definition is introduced.
>   - Skip post processing because this is not running kernel.
>   - Update documentation too.
> ---
>  tools/perf/Documentation/perf-probe.txt |    2 ++
>  tools/perf/builtin-probe.c              |   10 +++++++++-
>  tools/perf/util/probe-event.c           |    4 ++++
>  tools/perf/util/symbol-elf.c            |    2 +-
>  4 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/Documentation/perf-probe.txt b/tools/perf/Documentation/perf-probe.txt
> index 56db4d4..e6c9902 100644
> --- a/tools/perf/Documentation/perf-probe.txt
> +++ b/tools/perf/Documentation/perf-probe.txt
> @@ -36,6 +36,8 @@ OPTIONS
>  -k::
>  --vmlinux=PATH::
>  	Specify vmlinux path which has debuginfo (Dwarf binary).
> +	Only when using this with --definition, you can give an offline
> +	vmlinux file.
>  
>  -m::
>  --module=MODNAME|PATH::
> diff --git a/tools/perf/builtin-probe.c b/tools/perf/builtin-probe.c
> index 7a3d8c4..b4220cd 100644
> --- a/tools/perf/builtin-probe.c
> +++ b/tools/perf/builtin-probe.c
> @@ -654,8 +654,16 @@ __cmd_probe(int argc, const char **argv, const char *prefix __maybe_unused)
>  			return ret;
>  		}
>  		break;
> -	case 'a':
>  	case 'D':
> +		/*
> +		 * If user gives offline vmlinux, ignore buildid, since
> +		 * --definition doesn't change running kernel.
> +		 */
> +		if (symbol_conf.vmlinux_name)
> +			symbol_conf.ignore_vmlinux_buildid = true;
> +		/* fall through */
> +	case 'a':
> +
>  		/* Ensure the last given target is used */
>  		if (params.target && !params.target_used) {
>  			pr_err("  Error: -x/-m must follow the probe definitions.\n");
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index ad7094d..8dcec0c 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -674,6 +674,10 @@ post_process_kernel_probe_trace_events(struct probe_trace_event *tevs,
>  	char *tmp;
>  	int i, skipped = 0;
>  
> +	/* Skip post process if the target is an offline kernel */
> +	if (symbol_conf.ignore_vmlinux_buildid)
> +		return 0;
> +
>  	reloc_sym = kernel_get_ref_reloc_sym();
>  	if (!reloc_sym) {
>  		pr_warning("Relocated base symbol is not found!\n");
> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
> index a811c13..013cebf 100644
> --- a/tools/perf/util/symbol-elf.c
> +++ b/tools/perf/util/symbol-elf.c
> @@ -685,7 +685,7 @@ int symsrc__init(struct symsrc *ss, struct dso *dso, const char *name,
>  	}
>  
>  	/* Always reject images with a mismatched build-id: */
> -	if (dso->has_build_id) {
> +	if (dso->has_build_id && !symbol_conf.ignore_vmlinux_buildid) {
>  		u8 build_id[BUILD_ID_SIZE];
>  
>  		if (elf_read_build_id(elf, build_id, BUILD_ID_SIZE) < 0) {
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>