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Date: Wed, 6 Nov 2019 17:00:04 -0300
From: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Ingo Molnar <mingo@...hat.com>,
Steven Rostedt <rostedt@...dmis.org>,
linux-kernel@...r.kernel.org,
Tom Zanussi <tom.zanussi@...ux.intel.com>,
Ravi Bangoria <ravi.bangoria@...ux.ibm.com>,
Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH 5/5] perf probe: Trace a magic number if variable is not
found
Em Tue, Nov 05, 2019 at 09:17:28AM +0900, Masami Hiramatsu escreveu:
> Trace a magic number as immediate value if the target variable
> is not found at some probe points which is based on one probe
> event.
>
> This feature is good for the case if you trace a source code
> line with some local variables, which is compiled into several
> instructions and some of the variables are optimized out on
> some instructions. Even if so, with this feature, perf probe
> trace a magic number instead of such disappeared variables and
> fold those probes on one event.
This too depends on a function introduced in previous patches on hold.
- Arnaldo
> E.g. without this patch,
> # perf probe -D "pud_page_vaddr pud"
> Failed to find 'pud' in this function.
> Failed to find 'pud' in this function.
> Failed to find 'pud' in this function.
> Failed to find 'pud' in this function.
> Failed to find 'pud' in this function.
> Failed to find 'pud' in this function.
> Failed to find 'pud' in this function.
> Failed to find 'pud' in this function.
> Failed to find 'pud' in this function.
> Failed to find 'pud' in this function.
> Failed to find 'pud' in this function.
> Failed to find 'pud' in this function.
> Failed to find 'pud' in this function.
> Failed to find 'pud' in this function.
> Failed to find 'pud' in this function.
> Failed to find 'pud' in this function.
> p:probe/pud_page_vaddr_L0 _text+23480787 pud=%ax:x64
> p:probe/pud_page_vaddr_L0 _text+23808289 pud=%bp:x64
> p:probe/pud_page_vaddr_L0 _text+23558066 pud=%ax:x64
> p:probe/pud_page_vaddr_L0 _text+327957 pud=%r8:x64
> p:probe/pud_page_vaddr_L0 _text+348032 pud=%bx:x64
> p:probe/pud_page_vaddr_L0 _text+23816654 pud=%bx:x64
>
> With this patch,
> # perf probe -D "pud_page_vaddr pud" | head -n 10
> spurious_kernel_fault is blacklisted function, skip it.
> vmalloc_fault is blacklisted function, skip it.
> p:probe/pud_page_vaddr_L0 _text+23480787 pud=%ax:x64
> p:probe/pud_page_vaddr_L0 _text+148635 pud=\deade12d:x64
> p:probe/pud_page_vaddr_L0 _text+23808289 pud=%bp:x64
> p:probe/pud_page_vaddr_L0 _text+315510 pud=\deade12d:x64
> p:probe/pud_page_vaddr_L0 _text+23807045 pud=\deade12d:x64
> p:probe/pud_page_vaddr_L0 _text+23557349 pud=%ax:x64
> p:probe/pud_page_vaddr_L0 _text+313681 pud=%di:x64
> p:probe/pud_page_vaddr_L0 _text+313599 pud=\deade12d:x64
> p:probe/pud_page_vaddr_L0 _text+313477 pud=\deade12d:x64
> p:probe/pud_page_vaddr_L0 _text+323667 pud=\deade12d:x64
>
>
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
> tools/perf/util/probe-event.c | 2 +
> tools/perf/util/probe-event.h | 3 ++
> tools/perf/util/probe-finder.c | 62 +++++++++++++++++++++++++++++++++++++---
> tools/perf/util/probe-finder.h | 1 +
> 4 files changed, 63 insertions(+), 5 deletions(-)
>
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index 23db6786c3ea..ceeb75849311 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -46,7 +46,7 @@
> #define PERFPROBE_GROUP "probe"
>
> bool probe_event_dry_run; /* Dry run flag */
> -struct probe_conf probe_conf;
> +struct probe_conf probe_conf = { .magic_num = DEFAULT_PROBE_MAGIC_NUM };
>
> #define semantic_error(msg ...) pr_err("Semantic error :" msg)
>
> diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
> index 96a319cd2378..4f0eb3a20c36 100644
> --- a/tools/perf/util/probe-event.h
> +++ b/tools/perf/util/probe-event.h
> @@ -16,10 +16,13 @@ struct probe_conf {
> bool no_inlines;
> bool cache;
> int max_probes;
> + unsigned long magic_num;
> };
> extern struct probe_conf probe_conf;
> extern bool probe_event_dry_run;
>
> +#define DEFAULT_PROBE_MAGIC_NUM 0xdeade12d /* u32: 3735937325 */
> +
> struct symbol;
>
> /* kprobe-tracer and uprobe-tracer tracing point */
> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> index 2e3a468c8350..eff6063bebe6 100644
> --- a/tools/perf/util/probe-finder.c
> +++ b/tools/perf/util/probe-finder.c
> @@ -536,6 +536,14 @@ static int convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
> return 0;
> }
>
> +static void print_var_not_found(const char *varname)
> +{
> + pr_err("Failed to find the location of the '%s' variable at this address.\n"
> + " Perhaps it has been optimized out.\n"
> + " Use -V with the --range option to show '%s' location range.\n",
> + varname, varname);
> +}
> +
> /* Show a variables in kprobe event format */
> static int convert_variable(Dwarf_Die *vr_die, struct probe_finder *pf)
> {
> @@ -547,11 +555,11 @@ static int convert_variable(Dwarf_Die *vr_die, struct probe_finder *pf)
>
> ret = convert_variable_location(vr_die, pf->addr, pf->fb_ops,
> &pf->sp_die, pf->machine, pf->tvar);
> + if (ret == -ENOENT && pf->skip_empty_arg)
> + /* This can be found in other place. skip it */
> + return 0;
> if (ret == -ENOENT || ret == -EINVAL) {
> - pr_err("Failed to find the location of the '%s' variable at this address.\n"
> - " Perhaps it has been optimized out.\n"
> - " Use -V with the --range option to show '%s' location range.\n",
> - pf->pvar->var, pf->pvar->var);
> + print_var_not_found(pf->pvar->var);
> } else if (ret == -ENOTSUP)
> pr_err("Sorry, we don't support this variable location yet.\n");
> else if (ret == 0 && pf->pvar->field) {
> @@ -598,6 +606,8 @@ static int find_variable(Dwarf_Die *sc_die, struct probe_finder *pf)
> /* Search again in global variables */
> if (!die_find_variable_at(&pf->cu_die, pf->pvar->var,
> 0, &vr_die)) {
> + if (pf->skip_empty_arg)
> + return 0;
> pr_warning("Failed to find '%s' in this function.\n",
> pf->pvar->var);
> ret = -ENOENT;
> @@ -1348,6 +1358,44 @@ static int add_probe_trace_event(Dwarf_Die *sc_die, struct probe_finder *pf)
> return ret;
> }
>
> +static int fill_empty_trace_arg(struct perf_probe_event *pev,
> + struct probe_trace_event *tevs, int ntevs)
> +{
> + char **valp;
> + char *type;
> + int i, j, ret;
> +
> + for (i = 0; i < pev->nargs; i++) {
> + type = NULL;
> + for (j = 0; j < ntevs; j++) {
> + if (tevs[j].args[i].value) {
> + type = tevs[j].args[i].type;
> + break;
> + }
> + }
> + if (j == ntevs) {
> + print_var_not_found(pev->args[i].var);
> + return -ENOENT;
> + }
> + for (j = 0; j < ntevs; j++) {
> + valp = &tevs[j].args[i].value;
> + if (*valp)
> + continue;
> +
> + ret = asprintf(valp, "\\%lx", probe_conf.magic_num);
> + if (ret < 0)
> + return -ENOMEM;
> + /* Note that type can be NULL */
> + if (type) {
> + tevs[j].args[i].type = strdup(type);
> + if (!tevs[j].args[i].type)
> + return -ENOMEM;
> + }
> + }
> + }
> + return 0;
> +}
> +
> /* Find probe_trace_events specified by perf_probe_event from debuginfo */
> int debuginfo__find_trace_events(struct debuginfo *dbg,
> struct perf_probe_event *pev,
> @@ -1366,7 +1414,13 @@ int debuginfo__find_trace_events(struct debuginfo *dbg,
> tf.tevs = *tevs;
> tf.ntevs = 0;
>
> + if (pev->event && pev->nargs != 0 && immediate_value_is_supported())
> + tf.pf.skip_empty_arg = true;
> +
> ret = debuginfo__find_probes(dbg, &tf.pf);
> + if (ret >= 0 && tf.pf.skip_empty_arg)
> + ret = fill_empty_trace_arg(pev, tf.tevs, tf.ntevs);
> +
> if (ret < 0) {
> for (i = 0; i < tf.ntevs; i++)
> clear_probe_trace_event(&tf.tevs[i]);
> diff --git a/tools/perf/util/probe-finder.h b/tools/perf/util/probe-finder.h
> index 670c477bf8cf..11be10080613 100644
> --- a/tools/perf/util/probe-finder.h
> +++ b/tools/perf/util/probe-finder.h
> @@ -87,6 +87,7 @@ struct probe_finder {
> unsigned int machine; /* Target machine arch */
> struct perf_probe_arg *pvar; /* Current target variable */
> struct probe_trace_arg *tvar; /* Current result variable */
> + bool skip_empty_arg; /* Skip non-exist args */
> };
>
> struct trace_event_finder {
--
- Arnaldo
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