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Message-ID: <55DD269A.7030408@huawei.com>
Date: Wed, 26 Aug 2015 10:38:18 +0800
From: "Wangnan (F)" <wangnan0@...wei.com>
To: 平松雅巳 / HIRAMATU，MASAMI
<masami.hiramatsu.pt@...achi.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
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.
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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