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SubjectRe: [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@kernel.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@kernel.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@kernel.org>

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