Re: [PATCH 2/2] perf probe: Support probing at absolute address

["acme@kernel.org" <acme@kernel.org>]

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@huawei.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
 
> 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@huawei.com>
> >>Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> >>Cc: Ingo Molnar <mingo@redhat.com>
> >>Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> >>Cc: Namhyung Kim <namhyung@kernel.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
>