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Message-ID: <55DDBCDF.8050607@huawei.com>
Date: Wed, 26 Aug 2015 21:19:27 +0800
From: "Wangnan (F)" <wangnan0@...wei.com>
To: "acme@...nel.org" <acme@...nel.org>
CC: 平松雅巳 / HIRAMATU，MASAMI
<masami.hiramatsu.pt@...achi.com>,
"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
On 2015/8/26 21:02, acme@...nel.org wrote:
> Em Wed, Aug 26, 2015 at 10:38:18AM +0800, Wangnan (F) escreveu:
>> 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, I also think that using '+' is better, but will not dwell on
> this so as to make progress :-)
>
> - Arnaldo
>
Maybe we should support both of them, making '+0x1234' the core
syntax, and '0x1234' style as a syntax sugar. However I have worked
on this problem for nearly a full day but my main work should be BPF
related things...
Since Masami has acked all of the 6 v3 patches, if we still need '+' I can
bring it back with a new patch when I have time. However, same to you,
I don't think this should be a blocking problem.
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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