[PATCH -tip v2 2/2] perf-probe: Support basic dwarf-based operations on uprobe events

[Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>]

Support basic dwarf(debuginfo) based operations for uprobe events.
With this change, perf probe can analyze debuginfo of user
application binary to set up new uprobe event.
This allows perf-probe --add(with local variables, line numbers)
and --line works with -x option.
(Actually, --vars has already accepted -x option)

For example, the following command shows the probe-able lines of
a given user space function. Something that so far was only
available in the 'perf probe' tool for kernel space functions:
----
# ./perf probe -x perf --line map__load
<map__load@/home/fedora/ksrc/linux-2.6/tools/perf/util/map.c:0>
      0  int map__load(struct map *map, symbol_filter_t filter)
      1  {
      2         const char *name = map->dso->long_name;
                int nr;

      5         if (dso__loaded(map->dso, map->type))
      6                 return 0;

      8         nr = dso__load(map->dso, map, filter);
      9         if (nr < 0) {
     10                 if (map->dso->has_build_id) {
----

And this shows the available variables at the given line of
the function.
----
# ./perf probe -x perf --vars map__load:8
Available variables at map__load:8
        @<map__load+96>
                char*   name
                struct map*     map
                symbol_filter_t filter
        @<map__find_symbol+112>
                char*   name
                symbol_filter_t filter
        @<map__find_symbol_by_name+136>
                char*   name
                symbol_filter_t filter
        @<map_groups__find_symbol_by_name+176>
                char*   name
                struct map*     map
                symbol_filter_t filter
----

At last, we can now define a probe(s) with all available
variables on the given line.
----
# ./perf probe -x perf --add 'map__load:8 $vars'

Added new events:
  probe_perf:map__load (on map__load:8 with $vars)
  probe_perf:map__load_1 (on map__load:8 with $vars)
  probe_perf:map__load_2 (on map__load:8 with $vars)
  probe_perf:map__load_3 (on map__load:8 with $vars)

You can now use it in all perf tools, such as:

        perf record -e probe_perf:map__load_3 -aR sleep 1
----

Changes from previous version:
 - Add examples in the patch description.
 - Use .text section start address and dwarf symbol address
   for calculating the offset of given symbol, instead of
   searching the symbol in symtab again.
   With this change, we can safely handle multiple local
   function instances (e.g. scnprintf in perf).

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
---
 tools/perf/builtin-probe.c     |    2 -
 tools/perf/util/probe-event.c  |  151 ++++++++++++++++++++++++++++++++++++----
 tools/perf/util/probe-event.h  |    1 
 tools/perf/util/probe-finder.c |    1 
 4 files changed, 138 insertions(+), 17 deletions(-)

diff --git a/tools/perf/builtin-probe.c b/tools/perf/builtin-probe.c
index 5681266..20b3e15 100644
--- a/tools/perf/builtin-probe.c
+++ b/tools/perf/builtin-probe.c
@@ -425,7 +425,7 @@ int cmd_probe(int argc, const char **argv, const char *prefix __maybe_unused)
 	}
 
 #ifdef HAVE_DWARF_SUPPORT
-	if (params.show_lines && !params.uprobes) {
+	if (params.show_lines) {
 		if (params.mod_events) {
 			pr_err("  Error: Don't use --line with"
 			       " --add/--del.\n");
diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 05be5de..2f82267 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -172,6 +172,52 @@ const char *kernel_get_module_path(const char *module)
 	return (dso) ? dso->long_name : NULL;
 }
 
+/* Copied from unwind.c */
+static Elf_Scn *elf_section_by_name(Elf *elf, GElf_Ehdr *ep,
+				    GElf_Shdr *shp, const char *name)
+{
+	Elf_Scn *sec = NULL;
+
+	while ((sec = elf_nextscn(elf, sec)) != NULL) {
+		char *str;
+
+		gelf_getshdr(sec, shp);
+		str = elf_strptr(elf, ep->e_shstrndx, shp->sh_name);
+		if (!strcmp(name, str))
+			break;
+	}
+
+	return sec;
+}
+
+static int get_text_start_address(const char *exec, unsigned long *address)
+{
+	Elf *elf;
+	GElf_Ehdr ehdr;
+	GElf_Shdr shdr;
+	int fd, ret = -ENOENT;
+
+	fd = open(exec, O_RDONLY);
+	if (fd < 0)
+		return -errno;
+
+	elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
+	if (elf == NULL)
+		return -EINVAL;
+
+	if (gelf_getehdr(elf, &ehdr) == NULL)
+		goto out;
+
+	if (!elf_section_by_name(elf, &ehdr, &shdr, ".text"))
+		goto out;
+
+	*address = shdr.sh_addr - shdr.sh_offset;
+	ret = 0;
+out:
+	elf_end(elf);
+	return ret;
+}
+
 static int init_user_exec(void)
 {
 	int ret = 0;
@@ -186,6 +232,37 @@ static int init_user_exec(void)
 	return ret;
 }
 
+static int convert_exec_to_group(const char *exec, char **result)
+{
+	char *ptr1, *ptr2, *exec_copy;
+	char buf[64];
+	int ret;
+
+	exec_copy = strdup(exec);
+	if (!exec_copy)
+		return -ENOMEM;
+
+	ptr1 = basename(exec_copy);
+	if (!ptr1) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	ptr2 = strpbrk(ptr1, "-._");
+	if (ptr2)
+		*ptr2 = '\0';
+	ret = e_snprintf(buf, 64, "%s_%s", PERFPROBE_GROUP, ptr1);
+	if (ret < 0)
+		goto out;
+
+	*result = strdup(buf);
+	ret = *result ? 0 : -ENOMEM;
+
+out:
+	free(exec_copy);
+	return ret;
+}
+
 static int convert_to_perf_probe_point(struct probe_trace_point *tp,
 					struct perf_probe_point *pp)
 {
@@ -261,6 +338,40 @@ static int kprobe_convert_to_perf_probe(struct probe_trace_point *tp,
 	return 0;
 }
 
+static int add_exec_to_probe_trace_events(struct probe_trace_event *tevs,
+					  int ntevs, const char *exec)
+{
+	int i, ret = 0;
+	unsigned long offset, stext = 0;
+	char buf[32];
+
+	if (!exec)
+		return 0;
+
+	ret = get_text_start_address(exec, &stext);
+	if (ret < 0)
+		return ret;
+
+	for (i = 0; i < ntevs && ret >= 0; i++) {
+		offset = tevs[i].point.address - stext;
+		offset += tevs[i].point.offset;
+		tevs[i].point.offset = 0;
+		free(tevs[i].point.symbol);
+		ret = e_snprintf(buf, 32, "0x%lx", offset);
+		if (ret < 0)
+			break;
+		tevs[i].point.module = strdup(exec);
+		tevs[i].point.symbol = strdup(buf);
+		if (!tevs[i].point.symbol || !tevs[i].point.module) {
+			ret = -ENOMEM;
+			break;
+		}
+		tevs[i].uprobes = true;
+	}
+
+	return ret;
+}
+
 static int add_module_to_probe_trace_events(struct probe_trace_event *tevs,
 					    int ntevs, const char *module)
 {
@@ -305,15 +416,6 @@ static int try_to_find_probe_trace_events(struct perf_probe_event *pev,
 	struct debuginfo *dinfo;
 	int ntevs, ret = 0;
 
-	if (pev->uprobes) {
-		if (need_dwarf) {
-			pr_warning("Debuginfo-analysis is not yet supported"
-					" with -x/--exec option.\n");
-			return -ENOSYS;
-		}
-		return convert_name_to_addr(pev, target);
-	}
-
 	dinfo = open_debuginfo(target);
 
 	if (!dinfo) {
@@ -332,9 +434,14 @@ static int try_to_find_probe_trace_events(struct perf_probe_event *pev,
 
 	if (ntevs > 0) {	/* Succeeded to find trace events */
 		pr_debug("find %d probe_trace_events.\n", ntevs);
-		if (target)
-			ret = add_module_to_probe_trace_events(*tevs, ntevs,
-							       target);
+		if (target) {
+			if (pev->uprobes)
+				ret = add_exec_to_probe_trace_events(*tevs,
+						 ntevs, target);
+			else
+				ret = add_module_to_probe_trace_events(*tevs,
+						 ntevs, target);
+		}
 		return ret < 0 ? ret : ntevs;
 	}
 
@@ -654,9 +761,6 @@ static int try_to_find_probe_trace_events(struct perf_probe_event *pev,
 		return -ENOSYS;
 	}
 
-	if (pev->uprobes)
-		return convert_name_to_addr(pev, target);
-
 	return 0;
 }
 
@@ -1913,14 +2017,29 @@ static int convert_to_probe_trace_events(struct perf_probe_event *pev,
 					  int max_tevs, const char *target)
 {
 	struct symbol *sym;
-	int ret = 0, i;
+	int ret, i;
 	struct probe_trace_event *tev;
 
+	if (pev->uprobes && !pev->group) {
+		/* Replace group name if not given */
+		ret = convert_exec_to_group(target, &pev->group);
+		if (ret != 0) {
+			pr_warning("Failed to make a group name.\n");
+			return ret;
+		}
+	}
+
 	/* Convert perf_probe_event with debuginfo */
 	ret = try_to_find_probe_trace_events(pev, tevs, max_tevs, target);
 	if (ret != 0)
 		return ret;	/* Found in debuginfo or got an error */
 
+	if (pev->uprobes) {
+		ret = convert_name_to_addr(pev, target);
+		if (ret < 0)
+			return ret;
+	}
+
 	/* Allocate trace event buffer */
 	tev = *tevs = zalloc(sizeof(struct probe_trace_event));
 	if (tev == NULL)
diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
index f9f3de8..d481c46 100644
--- a/tools/perf/util/probe-event.h
+++ b/tools/perf/util/probe-event.h
@@ -12,6 +12,7 @@ struct probe_trace_point {
 	char		*symbol;	/* Base symbol */
 	char		*module;	/* Module name */
 	unsigned long	offset;		/* Offset from symbol */
+	unsigned long	address;	/* Actual address of the trace point */
 	bool		retprobe;	/* Return probe flag */
 };
 
diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index ffb657f..7db7e05 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -729,6 +729,7 @@ static int convert_to_trace_point(Dwarf_Die *sp_die, Dwfl_Module *mod,
 		return -ENOENT;
 	}
 	tp->offset = (unsigned long)(paddr - sym.st_value);
+	tp->address = (unsigned long)paddr;
 	tp->symbol = strdup(symbol);
 	if (!tp->symbol)
 		return -ENOMEM;