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Date: Wed, 26 Aug 2015 09:02:42 +0000
From: 平松雅巳 / HIRAMATU，MASAMI
<masami.hiramatsu.pt@...achi.com>
To: "'Wangnan (F)'" <wangnan0@...wei.com>,
"acme@...nel.org" <acme@...nel.org>
CC: "mingo@...hat.com" <mingo@...hat.com>,
"namhyung@...nel.org" <namhyung@...nel.org>,
"pi3orama@....com" <pi3orama@....com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/2] perf probe: Support probing at absolute address
> From: Wangnan (F) [mailto:wangnan0@...wei.com]
>
> On 2015/8/26 8:02, 平松雅巳 / HIRAMATU，MASAMI wrote:
> >> From: Wang Nan [mailto:wangnan0@...wei.com]
> >>
> >> It should be useful to allow 'perf probe' probe at absolute offset of
> >> a target. For example, when (u)probing at a instruction of a shared
> >> object in a embedded system where debuginfo is not avaliable but we
> >> know the offset of that instruction by manually digging.
> >>
> >> This patch enables following perf probe command syntax:
> >>
> >> # perf probe +0xffffffff811e6615
> >>
> >> And
> >>
> >> # perf probe /lib/x86_64-linux-gnu/libc-2.19.so +0xeb860
> > Why do we need "+" for the absolute address?
> > It seems that we can do it if we find that the given probe point
> > starts with "0x".
> >
> > Thanks,
>
> I will change 2/2 as you suggection.
>
> However, we can only ensure that in kernel side symbol never leading
> with '0x'. Although I don't think symbol leading with 0x is useful,
> it is still possible for a userspace program compiled and linked by
> a language other than C produces such symbol. '+' helps us separate
> address and function name semantically, make us don't rely on assumption
> on function names. If in future we do meet '0x' symbols, I think we still
> need the '+' syntax back. But we can do it at that time.
Agreed, if we really find the case, we can add '+' prefix support
just for an optional expression :)
Thank you!
>
> Thank you.
>
>
> >> In the above example, we don't need a anchor symbol, so it is possible
> >> to compute absolute addresses using other methods and then use
> >> 'perf probe' to create the probing points.
> >>
> >> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> >> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> >> Cc: Ingo Molnar <mingo@...hat.com>
> >> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> >> Cc: Namhyung Kim <namhyung@...nel.org>
> >> ---
> >> tools/perf/util/probe-event.c | 144 +++++++++++++++++++++++++++++++++++++----
> >> tools/perf/util/probe-event.h | 3 +
> >> tools/perf/util/probe-finder.c | 21 +-----
> >> 3 files changed, 138 insertions(+), 30 deletions(-)
> >>
> >> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> >> index 6c7e538..59de69a4 100644
> >> --- a/tools/perf/util/probe-event.c
> >> +++ b/tools/perf/util/probe-event.c
> >> @@ -1194,9 +1194,13 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> >> *ptr++ = '\0';
> >> }
> >>
> >> - tmp = strdup(arg);
> >> - if (tmp == NULL)
> >> - return -ENOMEM;
> >> + if (arg[0] == '\0')
> >> + tmp = NULL;
> >> + else {
> >> + tmp = strdup(arg);
> >> + if (tmp == NULL)
> >> + return -ENOMEM;
> >> + }
> >>
> >> if (file_spec)
> >> pp->file = tmp;
> >> @@ -1283,11 +1287,6 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> >> return -EINVAL;
> >> }
> >>
> >> - if (pp->offset && !pp->function) {
> >> - semantic_error("Offset requires an entry function.\n");
> >> - return -EINVAL;
> >> - }
> >> -
> >> if (pp->retprobe && !pp->function) {
> >> semantic_error("Return probe requires an entry function.\n");
> >> return -EINVAL;
> >> @@ -1299,6 +1298,11 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
> >> return -EINVAL;
> >> }
> >>
> >> + if (!pp->function && !pp->offset && !pp->file) {
> >> + semantic_error("Absolute address should not be zero.\n");
> >> + return -EINVAL;
> >> + }
> >> +
> >> pr_debug("symbol:%s file:%s line:%d offset:%lu return:%d lazy:%s\n",
> >> pp->function, pp->file, pp->line, pp->offset, pp->retprobe,
> >> pp->lazy_line);
> >> @@ -1609,7 +1613,7 @@ error:
> >> static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> >> {
> >> char *buf, *tmp;
> >> - char offs[32] = "", line[32] = "", file[32] = "";
> >> + char offs[32] = "", line[32] = "", file[32] = "", addr[32] = "";
> >> int ret, len;
> >>
> >> buf = zalloc(MAX_CMDLEN);
> >> @@ -1622,6 +1626,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> >> if (ret <= 0)
> >> goto error;
> >> }
> >> + if (!pp->function) {
> >> + ret = e_snprintf(addr, 32, "0x%lx", pp->offset);
> >> + if (ret <= 0)
> >> + goto error;
> >> + }
> >> if (pp->line) {
> >> ret = e_snprintf(line, 32, ":%d", pp->line);
> >> if (ret <= 0)
> >> @@ -1639,9 +1648,11 @@ static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
> >> goto error;
> >> }
> >>
> >> - if (pp->function)
> >> - ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s", pp->function,
> >> - offs, pp->retprobe ? "%return" : "", line,
> >> + if (pp->function || pp->offset)
> >> + ret = e_snprintf(buf, MAX_CMDLEN, "%s%s%s%s%s",
> >> + pp->function ? : addr,
> >> + pp->function ? offs : "",
> >> + pp->retprobe ? "%return" : "", line,
> >> file);
> >> else
> >> ret = e_snprintf(buf, MAX_CMDLEN, "%s%s", file, line);
> >> @@ -1786,6 +1797,11 @@ char *synthesize_probe_trace_command(struct probe_trace_event *tev)
> >> if (tev->uprobes)
> >> ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s:0x%lx",
> >> tp->module, tp->address);
> >> + else if (tp->symbol[0] == '0' && tp->symbol[1] == 'x')
> >> + /* Absolute address. See try_to_find_absolute_address() */
> >> + ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s0x%lx",
> >> + tp->module ?: "", tp->module ? ":" : "",
> >> + tp->address);
> >> else
> >> ret = e_snprintf(buf + len, MAX_CMDLEN - len, "%s%s%s+%lu",
> >> tp->module ?: "", tp->module ? ":" : "",
> >> @@ -2572,6 +2588,87 @@ err_out:
> >> goto out;
> >> }
> >>
> >> +static int try_to_find_absolute_address(struct perf_probe_event *pev,
> >> + struct probe_trace_event **tevs)
> >> +{
> >> + struct perf_probe_point *pp = &pev->point;
> >> + struct probe_trace_event *tev;
> >> + struct probe_trace_point *tp;
> >> + int i, err;
> >> +
> >> + if (perf_probe_event_need_dwarf(pev) || pev->point.function)
> >> + return -EINVAL;
> >> +
> >> + /*
> >> + * This is 'perf probe /lib/libc.so +0xabcd'. Try to probe at
> >> + * absolute address.
> >> + *
> >> + * Only one tev can be generated by this.
> >> + */
> >> + *tevs = zalloc(sizeof(*tev));
> >> + if (!*tevs)
> >> + return -ENOMEM;
> >> +
> >> + tev = *tevs;
> >> + tp = &tev->point;
> >> +
> >> + /*
> >> + * Don't use tp->offset, use address directly, because
> >> + * in synthesize_probe_trace_command() address cannot be
> >> + * zero.
> >> + */
> >> + tp->address = pev->point.offset;
> >> + tp->retprobe = pp->retprobe;
> >> + tev->uprobes = pev->uprobes;
> >> +
> >> + err = -ENOMEM;
> >> + /* Give it a '0x' leading symbol name */
> >> + if (asprintf(&tp->symbol, "0x%lx", tp->address) < 0)
> >> + goto errout;
> >> +
> >> + /* For kprobe, check range */
> >> + if ((!tev->uprobes) &&
> >> + (kprobe_warn_out_range(tev->point.symbol,
> >> + tev->point.address))) {
> >> + err = -EACCES;
> >> + goto errout;
> >> + }
> >> +
> >> + if (asprintf(&tp->realname, "abs_%lx", tp->address) < 0)
> >> + goto errout;
> >> +
> >> + if (pev->target) {
> >> + tp->module = strdup(pev->target);
> >> + if (!tp->module)
> >> + goto errout;
> >> + }
> >> +
> >> + if (tev->group) {
> >> + tev->group = strdup(pev->group);
> >> + if (!tev->group)
> >> + goto errout;
> >> + }
> >> +
> >> + if (pev->event) {
> >> + tev->event = strdup(pev->event);
> >> + if (!tev->event)
> >> + goto errout;
> >> + }
> >> +
> >> + tev->nargs = pev->nargs;
> >> + for (i = 0; i < tev->nargs; i++)
> >> + copy_to_probe_trace_arg(&tev->args[i], &pev->args[i]);
> >> +
> >> + return 1;
> >> +
> >> +errout:
> >> + if (*tevs) {
> >> + clear_probe_trace_events(*tevs, 1);
> >> + *tevs = NULL;
> >> + }
> >> + return err;
> >> +}
> >> +
> >> bool __weak arch__prefers_symtab(void) { return false; }
> >>
> >> static int convert_to_probe_trace_events(struct perf_probe_event *pev,
> >> @@ -2588,6 +2685,10 @@ static int convert_to_probe_trace_events(struct perf_probe_event *pev,
> >> }
> >> }
> >>
> >> + ret = try_to_find_absolute_address(pev, tevs);
> >> + if (ret > 0)
> >> + return ret;
> >> +
> >> if (arch__prefers_symtab() && !perf_probe_event_need_dwarf(pev)) {
> >> ret = find_probe_trace_events_from_map(pev, tevs);
> >> if (ret > 0)
> >> @@ -2758,3 +2859,22 @@ end:
> >> return ret;
> >> }
> >>
> >> +int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
> >> + struct perf_probe_arg *pvar)
> >> +{
> >> + tvar->value = strdup(pvar->var);
> >> + if (tvar->value == NULL)
> >> + return -ENOMEM;
> >> + if (pvar->type) {
> >> + tvar->type = strdup(pvar->type);
> >> + if (tvar->type == NULL)
> >> + return -ENOMEM;
> >> + }
> >> + if (pvar->name) {
> >> + tvar->name = strdup(pvar->name);
> >> + if (tvar->name == NULL)
> >> + return -ENOMEM;
> >> + } else
> >> + tvar->name = NULL;
> >> + return 0;
> >> +}
> >> diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
> >> index 83ee95e..174a3cf 100644
> >> --- a/tools/perf/util/probe-event.h
> >> +++ b/tools/perf/util/probe-event.h
> >> @@ -156,4 +156,7 @@ int e_snprintf(char *str, size_t size, const char *format, ...)
> >> /* Maximum index number of event-name postfix */
> >> #define MAX_EVENT_INDEX 1024
> >>
> >> +int copy_to_probe_trace_arg(struct probe_trace_arg *tvar,
> >> + struct perf_probe_arg *pvar);
> >> +
> >> #endif /*_PROBE_EVENT_H */
> >> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> >> index 7b80f8c..29c43c068 100644
> >> --- a/tools/perf/util/probe-finder.c
> >> +++ b/tools/perf/util/probe-finder.c
> >> @@ -553,24 +553,9 @@ static int find_variable(Dwarf_Die *sc_die, struct probe_finder *pf)
> >> char buf[32], *ptr;
> >> int ret = 0;
> >>
> >> - if (!is_c_varname(pf->pvar->var)) {
> >> - /* Copy raw parameters */
> >> - pf->tvar->value = strdup(pf->pvar->var);
> >> - if (pf->tvar->value == NULL)
> >> - return -ENOMEM;
> >> - if (pf->pvar->type) {
> >> - pf->tvar->type = strdup(pf->pvar->type);
> >> - if (pf->tvar->type == NULL)
> >> - return -ENOMEM;
> >> - }
> >> - if (pf->pvar->name) {
> >> - pf->tvar->name = strdup(pf->pvar->name);
> >> - if (pf->tvar->name == NULL)
> >> - return -ENOMEM;
> >> - } else
> >> - pf->tvar->name = NULL;
> >> - return 0;
> >> - }
> >> + /* Copy raw parameters */
> >> + if (!is_c_varname(pf->pvar->var))
> >> + return copy_to_probe_trace_arg(pf->tvar, pf->pvar);
> >>
> >> if (pf->pvar->name)
> >> pf->tvar->name = strdup(pf->pvar->name);
> >> --
> >> 1.8.3.4
>
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