Re: [PATCH 2/2] perf probe: Support probing at absolute address
From: Wangnan (F)
Date: Wed Aug 26 2015 - 09:19:55 EST
On 2015/8/26 21:02, acme@xxxxxxxxxx wrote:
Em Wed, Aug 26, 2015 at 10:38:18AM +0800, Wangnan (F) escreveu:
On 2015/8/26 8:02, åæéå / HIRAMATUïMASAMI wrote:
From: Wang Nan [mailto:wangnan0@xxxxxxxxxx]
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@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
---
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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