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

[Wang Nan <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

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